COURSE NOTES FOR AS495Lpages.erau.edu/~rogers/as471/as495Text.doc · Web viewThe 8-point roll is an aileron roll where the roll rate is momentarily halted every 45o of roll, i.e.,

COURSE TEXT

ALL ATTITUDE FLIGHT

AND

UPSET RECOVERY

© 2004 R. Rogers

Drs. Rogers is an Aeronautical Science Department faculty member at Embry-Riddle Aeronautical University, Daytona Beach, Florida. Educators including flight instructors are free to use the materials contained herein for non-profit or not-for-profit activities. Any other use of these materials may constitute a copyright violation. Feedback on our course is invited. Send email to

[email protected]

TABLE OF CONTENTS

Subject PageI. Course Introduction 2II. Introduction to Microsoft Flight Simulator 3III. Aerobatics Maneuvers 5IV. Upset Aerodynamics 15V. Airplane Upset Recovery Techniques 35VI. Causes of Upsets 42VII. Loss of Control Accident Analyses 54VIII. Annotated Bibliography 80

COURSE WEB SITE

http://faculty.erau.edu/rogersr/as495

Revised 30 August 2004


mailto:[email protected]

I. COURSE INTRODUCTION

Purpose. This course is a low-cost introduction to all attitude flight and to upset recovery (also called recovery from unusual attitudes). To this end, it uses desktop computers running inexpensive flight simulation software (currently the Microsoft Flight Simulator 2002 Professional Edition). While intended for pilots embarking on an airline career, the course contains information of interest to aviators in general. By all attitude flight, we mean upright or inverted flight throughout the subsonic flight regime, including bank angles up to and including 180o, and pitch angles that reach 90o nose-up or 90o nose-down. An upset, or unusual attitude, occurs when an aircraft reaches an attitude or airspeed outside its normal operating regime. In general, an unusual attitude is unanticipated by the flight crew, and has a distinct potential to compromise safety-of-flight. For airliners, such an attitude can involve a pitch angle as small as 15-20o, and a bank angle of only 35-45o. Indeed, a 10o nose-down attitude in an airliner at high altitude and airspeed above normal cruise mach can rapidly progress toward a dangerous situation.

Prerequisite Knowledge. Since recovery from unusual attitudes requires a through knowledge of instrument flight, a pilot should be instrument qualified before undertaking this course. ERAU students taking this course for credit should hold an instrument airplane rating and should have completed AS309, Basic Aerodynamics. In addition, they should be familiar with the Microsoft Flight Simulator or be able to learn how to use the software with minimal supervision.

Organization. The course content is divided into six parts. Currently you are reading the first part, an introduction to the course. The second part is a brief introduction to the Microsoft Flight Simulator 2002 Professional Edition. The third part of the course introduces basic aerobatic maneuvers: low level constant altitude flight at bank angles up to 180o; inverted flight; loops; half and full Cuban eights; aileron and barrel rolls, and Immelmanns. The goal here is to help a pilot become acquainted with the cues—both visual and those provided by aircraft instruments—available to control an aircraft throughout the flight regime. The fourth part is a review of Aerodynamics, while the fifth treats relevant loss of control accidents in airliners, and is a motivation for the sixth and last part of the course, which focuses on techniques for upset recovery in airliners. An appended seventh section lists potential topics for course projects.

Lab Sessions. The course requires eleven flights on the Microsoft Flight Simulator, each of duration about one hour. The flight syllabus is given below.

Flight Focus Brief DescriptionFam 1 Sim and A/C Fam; Steep Turns System Familiarization; Upright and Inverted Steep Turns

Aero 1,2 VFR Acrobatics Aileron Roll, Barrel Roll, Wingover, Loop, Half and Full Cuban Eight, Immelmann, Split-S with Visual horizon

Aero 3,4 IFR Aerobatics Aero 1 and 2 Maneuvers by Instrument ReferenceAero 5 Aerobatics Check Flight Precision VFR and IFR Aerobatics Check FlightUpset 1 Upset Recovery Fighter Aircraft Upset Recovery TechniquesUpset 2 Upset Recovery B767 Aircraft Fam; Airline Upset Recovery TechniquesUpset 3 Upset Recovery Airline Upset Recovery Techniques (IFR)Upset 4 Upset Recovery Upset Recovery Check Ride PracticeUpset 5 Upset Recovery Check Flight Fighter/Transport Upset Recovery Check Flight

Disclaimer. This course is NOT a substitute for experience in an airplane. While we believe the course will enable a pilot to learn aerobatic flight and in-flight upset recovery faster, no evidence currently exists to support this belief. No flight simulator known to the author faithfully reproduces all the cues available to pilots in all attitude flight. In particular, the Microsoft Flight Simulator provides rather accurate visual cues and realistic instrument responses; however, it is notably lacking in faithfulness with respect to G-forces and responses of the airplane to throttle changes, control inputs, and changes in AOA/induced drag, among other shortcomings. That said, full motion simulators used by airlines to teach upset recovery techniques suffer in lesser degree from some of the same shortcomings.

AS495L Class Text Page - 2 (Revised 30 August 2004)

II. INTRODUCTION TO THE MICROSOFT FLIGHT SIMULATOR

Preliminary Comments

Microsoft Flight Simulator 2002 Professional Edition (MFS 2002) is a first rate piece of software at a low cost. The simulator views we have developed for training flights provide visually realistic cues for aerobatics and upset recovery training. Bear in mind, however, that even with three forward looking windows open—affording a forward field of vision exceeding 90o—what you see from a simulated fighter cockpit is severely restricted compared with what you can see from a real-world airplane. This problem is much less significant when you are flying a simulated airliner, since visibility from a real-world airliner cockpit is already very severely restricted.

Another drawback is that both fighter and airline type aircraft in MFS 2002 respond more erratically to control stick movement than do real world airplanes, a phenomenon more pronounced in airliners than in fighters, however. As an example, 8-point aileron rolls are fairly easy to perform in a real-world fighter, and quite difficult in a simulated fighter (the simulator control stick is so sensitive that stopping a roll precisely on increments of 45o requires a lot of practice). In fact, even 4-point rolls are challenging to perform in the simulator.

Other considerations include the fact that G forces do not decrease realistically when stick back pressure is released; simulated aircraft do not decelerate as rapidly as real-world aircraft when thrust is reduced at low altitude and high airspeed; and RPM required in simulated fighter-type aircraft to maintain a given flight regime is significantly less than in real-world aircraft.

For all this, the bottom line is that you can learn a lot about aerobatics and unusual attitude recovery by flying MFS 2002. You may also develop some habits about throttle and stick control that will need modification when you begin similar training in a real airplane, but we think that overall the gains from flying the simulator will far outweigh the drawbacks. In time, there will probably be an aerobatics flight course at ERAU Daytona Beach. At that point, we will be able to test the validity of our theory that MFS 2002 is an excellent way to introduce student aviators to all attitude flight.

Using the Simulator

Introductory Comments. Many if not most Air Science students are already familiar with MFS 2002. If you’re not one of these people, you will need to spend some time learning the features of the simulator. This isn’t difficult, but it may require you to schedule a few extra sessions in the lab or on your own or your friend’s computer. We anticipate that you will be able learn what you need to know about MSF 2002 pretty much on your own. However, feel free to ask questions of the lab instructors, and if necessary, of the course instructors. If you have a home computer with good enough graphics capability to run MFS 2002, you should very definitely consider buying and installing the software.

When you arrive for a flight in the lab (scheduled or unscheduled), the procedures to follow are straightforward. (The foregoing assumes MFS 2002 is already running; if this isn’t the case, first start the software.)

1. Receive a computer assignment from the lab instructor; if no instructor is present, sit down at an available computer.

2. From the start screen, click Select a Flight.3. When the Select a Flight screen appears, click My Saved Flights in the Choose a Category list.4. From the Choose a Flight list, pick the training flight you want.5. You will find yourself in the cockpit in position at the takeoff end of the runway. Take off and

proceed with the maneuvers relevant to your flight. (Use slew to depart the field if time is short.)6. When you complete your maneuvers or when time runs out, pause the flight (You may fly or slew

back to the field and land if time permits, assuming you can find the field using visual navigation).7. Select File in the menu bar (ALT key toggles the menu bar on/off in full screen mode).


8. Click End Flight on the File pull-down menu. (Leave the Select a Flight screen on the display.)Note: Please do NOT save any flights on the lab machines. If you want to port the course flights saved on a lab machine to another computer, ask the lab assistants for help. You will need first to install any airplanes not already on your personal installation of MFS 2002. Course saved flight and weather files and zipped aircraft software can be downloaded from the course web site. Each saved flight has two files (.flt and .wx extensions). These two files should be placed in the ..\FS2002\flights\myflights directory of your Flight Simulator installation. In a default installation, the full path is ordinarily C:\Program Files\Microsoft Games\ FS2002\flights\myflights. To install a new aircraft, unzip the aircraft file and follow the installation directions. The gauges should be installed in the ..\aircraft\gauges directory.

Some Important MFS 2002 Key Commands. The simulator has many key commands to assist you in operating the software and flying the airplane. To see a full list of these commands, select Aircraft on the menu bar at the in-flight screen, and then Kneeboard in the resulting pull-down menu. (See the table below: F10 is a shortcut for these two actions.) You will probably want to make your own list of the key commands you use frequently in flight. We list below some of the commands we have found most useful when the simulator is in the in-flight mode (i.e., when you are sitting in the simulated airplane’s cockpit). It wouldn’t be a bad idea to have this page of the notes open on the table next to you when you are using MFS 2002.

Command ResultSimulator Controls

ALT Toggles menu bar on/off at top of screen (flight is paused when menu is on)CTRL - ; Resets simulator to beginning of saved flight

SHIFT - Z Cycles between various presentations of statistics at top of screenP Toggles between pause/fly simulator

F10 Open Kneeboard and cycle through its four tabs. (Fifth F10 closes kneeboard.)Aircraft Controls

. (Period) Release parking brake when set; apply brakes when parking brake is releasedF11 Apply left brakeF12 Apply right brake

CTRL - . Set parking brakeG Toggle landing gear up/downF5 Retract flaps fullyF6 Retract flaps in incrementsF7 Extend flaps in incrementsF8 Extend flaps fully/ Toggles spoilers (airbrakes) between extend/retractI Toggles smoke on/off

View CommandsW Cycle instrument through instrument panel presentations (including off)S Cycle views in the currently selected view window (must be in cockpit mode)

Slew CommandsY Toggle slew mode on/off

SPACEBAR Heading north; straight and level; cancel current commanded slew movementNum Pad 5 Freeze all slew movementNum Pad 8 Move forwardNum Pad 2 Move backwardNum Pad 4 Move leftNum Pad 8 Move RightF3 (or Q) Move up slowly

F4 Move up quicklyA Move down slowlyF1 Move down quicklyF2 Freeze vertical movement


III. AEROBATIC MANEUVERS

SAFETY NOTE: DON’T QUALIFY FOR THE DARWIN AWARD

PRACTICE THE FOLLOWING MANEUVERS ONLY IN A SIMULATOR. IN PARTICULAR, ACTUAL LOW LEVEL FLIGHT CAN BE VERY HAZARDOUS AND NOT INFREQUENTLY INVOLVES VIOLATIONS OF FARS. (STOP A MINUTE TO RECALL THE MANY TIMES YOU FLEW THE SIMULATOR AIRCRAFT INTO THE TERRAIN WHILE FLYING CLOSE TO THE GROUND.) MANY PILOTS INCLUDING BLUE ANGELS AND THUNDERBIRDS HAVE BEEN KILLED DUE TO INADVERTENT TERRAIN CONTACT DURING LOW LEVEL FLIGHT. REGRETTABLY, IT IS LIKELY THAT MORE PILOTS IN ALL CATEGORIES WILL BE KILLED IN THE FUTURE. MANY FLYING MANEUVERS ARE BEST LEARNED THROUGH AIRBORNE EXPERIENCE. FLYING INTO THE GROUND IS NOT ONE OF THESE MANEUVERS.

NEVER ATTEMPT ANY KIND OF AEROBATIC OR NON-STANDARD MANEUVERING IN AN AIRPLANE UNLESS A FLIGHT INSTRUCTOR QUALIFIED TO INSTRUCT YOU IN AEROBATIC FLIGHT ACCOMPANIES YOU. AN EMBRY-RIDDLE STUDENT PILOT WAS KILLED AROUND 1990 AT DAYTONA BEACH WHILE INVOLVED IN UNAUTHORIZED LOW LEVEL FLIGHT. HE ACCIDENTLY FLEW A C-172 INTO HIS GIRLFRIEND’S HOUSE IN FLAGLER COUNTY WHILE MAKING A LOW PASS TO IMPRESS HER. MANY OTHER PILOTS, INCLUDING A NUMBER OF MILITARY PILOTS KNOWN PERSONALLY TO THE AUTHOR, HAVE LOST THEIR LIVES BY IGNORING SIMPLE SAFETY CONSIDERATIONS ABOUT UNUSUAL ATTITUDE FLIGHT. ONE OF THE MOST IMPORTANT OF THESE SAFETY CONSIDERATIONS IS THAT IF YOU ARE A PILOT, YOU ARE NOT NEARLY AS HOT A PILOT AS YOU THINK YOU ARE, AND SHOULD ACT ACCORDINGLY. A CORRELARY TO THIS IDEA IS THAT YOU DON’T REALLY BELIEVE WHAT YOU JUST READ IN THE LAST SENTENCE. REMEMBER THE FAMOUS AVIATION MAXIM: “THERE ARE OLD PILOTS, AND THERE ARE BOLD PILOTS, BUT THERE ARE NO OLD, BOLD PILOTS.”

Terminology, Abbreviations, &c.

1. AI = attitude indicator; AS = airspeed indicator; DG = directional gyro (gyro compass); VSI = vertical speed indicator; TI = turn indicator (also a roll indicator); G = g meter.

2. Upright (inverted) flight = A/C bank angle less than (more than) 900, or pitch angle less than (more than) 90o with bank angle less than 90o.

3. Nose up (nose down) = nose up (nose down) refer to the nose attitude relative to the horizon. Note that nose position is NOT necessarily relative to pilot’s orientation in cockpit, depending on whether the aircraft is in upright or inverted flight. In both upright and inverted flight, nose up (down) means to aircraft’s nose is above (below) the horizon and the AI is in the light (dark) area. In upright straight and level flight, the pilot of course must pull back (push forward) on the stick to achieve a nose up (nose down) attitude. In inverted straight and level flight, however, the pilot must push forward (pull back) on the stick to achieve a nose up (nose down) attitude.

4. Nose rising (nose falling) = movement of nose position relative to the horizon, not the pilot’s orientation in the cockpit. In upright straight and level flight, a pilot pushes forward (pulls back) on the control stick to stop nose rising (nose falling) motion. In inverted straight and level flight, to stop nose rising (nose falling) motion, the pilot must pull back (push forward) on the stick.


5. Wing up (down) = wing position relative to the horizon, not to the pilot’s position in the cockpit. (See notes immediately following on Upright vs. Inverted Flight.)


Upright vs. Inverted Flight

From straight and level upright flight, inverted flight can be achieved by exceeding 90o of roll (without changing altitude) or 90o of pitch (without rolling). If you are in upright straight and level flight, a roll of 180o, together with proper pitch control, will put you in inverted straight and level flight. You can achieve the same attitude by pulling back on the stick. As the airplane goes past the vertical position (90o of pitch), the AI “flips” so that the light part is toward the pilot’s feet and the dark part toward the pilot’s head. The DI also reverses 180o. You are now in inverted flight with a very nose high attitude. If you continue stick backpressure, the nose will fall through to the horizon, at which time—if you stop the nose from falling further—you will be in inverted straight and level flight. Note that in the vertical maneuver, you converted airspeed (kinetic energy) to altitude (potential energy). That is, airspeed decreased and altitude increased. You didn’t roll at all. (The vertical maneuver described is the first half of a loop, of course, or all of an Immelmann except the final 180o roll from an inverted to upright position.)

In upright straight and level flight, you pull back on the stick to move the nose up, and push forward to move it down (inducing negative G forces, of course). The light portion of the AI is oriented toward the top of the instrument panel. If the reference airplane on the AI is in the light (dark) portion, the nose is above (below) the horizon. Visually, the sky is oriented toward the pilot’s head and the ground toward the pilot’s feet. To drop the right (left) wing, you push right (left) on the control stick. When the right (left) wing drops, the aircraft turns toward the pilot’s right (left); the AI shows the right (left) wing in the dark area; the DG tracks clockwise (counterclockwise), and the TI shows a right (left) turn.

In inverted straight and level flight, lift is being developed by excess static pressure acting on the upper surface of the wing (as opposed to the lower surface in upright flight). Thus some of the control and instrument parameters of upright flight are “reversed.” you pull back on the stick to move the nose down, and push forward to move it up (inducing negative G forces). When the nose is moving up (down), it is moving toward the pilot’s feet (head). The light portion of the AI is oriented toward the bottom of the instrument panel. Of course, if the reference airplane on the AI is in the light (dark) portion, the nose is still above (below) the horizon. Visually, the sky is oriented toward the pilot’s feet and the ground toward the pilot’s head. To drop the right (left) wing, you push left (right) on the control stick. When the right (left) wing drops, the aircraft still turns toward the pilot’s right (left); the AI still shows the right (left) wing in the dark area. However, the DG tracks counterclockwise (clockwise.) while the TI still shows a right (left) turn even though the aircraft is tracking counterclockwise (clockwise). If it surprises you that the DG can track counterclockwise (clockwise) when the aircraft is turning to the pilot’s right (left) hand side and the TI shows a left (right) turn, remember that the pilot—like the airplane—is inverted. As discussed in above, if the aircraft and pilot were upright, counterclockwise (clockwise) DG motion would correspond to a turn to the pilot’s left (right) and the TI would show a turn to the left (right).

Finally, recall that both the AI and the DG “flip” whenever the pitch angle exceeds 90o nose up or nose down with bank angle not equal to 90o. For example, in a loop, the AI flips from upright to inverted when the airplane passes through the vertical nose up; at the same time, the DG flips to show the reciprocal of the current heading. When passing through the vertical nose down in the same loop, the AI flips from inverted to upright, and the DG flips to its reciprocal, i.e., flips 180o to the original heading.

The following table summarizes instrument responses in level coordinated turns in upright (+1.0 G force) and inverted flight (-1.0 G force). The fighter aircraft we currently use for the course in MF 2002 doesn’t have a turn indicator. You can verify the following however, by choosing a simulated aircraft that has the required instrumentation.

Turn Instrument ResponsesUpright right wing down DG tracks clockwise; TI shows starboard (right) turn; Positive G.Upright left wing down DG tracks counterclockwise; TI shows port (left) turn; Positive G.Inverted left wing down DG tracks clockwise; TI shows port (left) turn; Negative G.

Inverted right wing down DG tracks counterclockwise; TI shows starboard (right) turn; Negative G


Table Shows Turn Directions in Inverted Flight at Negative G of -1.0 or less


The comments above assume negative G in inverted flight; i.e., assume straight and level inverted flight. However, if you think a bit—perhaps draw some pictures and watch the simulator response with spot aircraft windows open—you will see that the situation with positive G inverted flight turn is a little different. If your right wing is down in inverted flight when lift is being developed on the underside of the wing (i.e., at positive G), you will turn to your right (clockwise on the DG). If your left wing is down, you will turn to your left (counterclockwise on the DG). Note also that positive G inverted flight means the nose is falling toward or below the horizon, depending of course on the nose position of the aircraft at the moment the inverted flight attitude is achieved. The following table summarizes these ideas.

Turn at Positive G Instrument ResponsesUpright right wing down DG tracks clockwise; TI shows starboard (right) turnUpright left wing down DG tracks counterclockwise; TI shows port (left) turn

Inverted right wing down DG tracks clockwise; TI shows starboard (right) turnInverted left wing down DG tracks counterclockwise; TI shows port (left) turn

Table Shows Turn Directions in Inverted Flight at Positive G of 1.0 or Greater

The following ideas can be summed up in a simple statement: An aircraft—upright or inverted—turns whenever its lift vector is oriented away from the vertical, and it turns in the direction that the lift vector is oriented.

Low Level Flight

You will practice maintaining (as closely as possible) a constant low altitude (100-200 feet AGL) in flight over mountainous terrain. This involves maneuvering up and down canyons at bank angles up to 180o; pitch angles may vary as much as 45o nose up or nose down. This type of flight is accomplished primarily using visual cues, with aircraft instruments as a backup. The purpose of this activity is to help you become accustomed to steep and constantly varying bank and pitch angles. Note that the G force on the aircraft will change with bank angle, and will probably vary between +4-5 G and –1 G. When cresting a ridge with a steep drop off on the far side, you will need to roll inverted to avoid gaining altitude, since pushing over in wings level flight at the top of the ridge to start “downhill” produces uncomfortable negative G’s in a real airplane. Once you are inverted, you will need to “pull through” on the stick to move the nose somewhat below the horizon; then roll out as the aircraft’s longitudinal axis becomes parallel with the ground. Be careful not to fly into the ground by pulling through too hard or rolling out late.

While maneuvering, it is easy to “manhandle” the controls of the simulator without much evidence that you have done anything improper, i.e., something that might be dangerous in a real airplane. Watch the G meter; if you apply excessive G force in a real airplane, there is a danger of causing structural damage or even breaking the wing spars and removing the wings from the aircraft. Every airplane has a maximum allowable G and an ultimate G, the latter of which is the point where the danger of catastrophic structural failure becomes a major concern.

At higher altitudes and lower airspeeds, high G may not be available, since an accelerated stall occurs first. A number of real world swept-wing fighters will experience a post-stall departure if the pilot fails to release stick backpressure when an accelerated stall occurs. Such a departure involves a loss of control with rapid and prolonged changes in roll and pitch angles. In short, the airplane gyrates wildly. Recovery may be initiated by releasing backpressure and lowering the angle of attack—in essence, by letting go of the stick. We might refer to this recovery technique as the “hands on head” procedure. Failure to release back pressure after an accelerated stall—particularly if the ailerons/spoilers are positioned for a roll—in some aircraft can lead to rapid loss of airspeed and a spin, recovery from which typically is problematic in swept-wing aircraft. We have not seen MFS 2002 simulate a post-stall departure, but in the real world inadvertent post-stall departure maneuvers are not at all uncommon. Some swept-wing fighters depart quickly if the pilot keeps on stick back pressure through an accelerated stall; others simply remain stalled without experiencing uncalled roll and pitch.


Inverted Flight Maneuver

To achieve inverted straight and level flight from upright straight and level flight, raise the nose slightly and roll quickly to the inverted position. It will be necessary to use forward stick to keep the nose slightly above the horizon while inverted. (Lift is being developed on the top of the wings, which are oriented toward the ground in inverted flight.)

Pilot Procedures. The roll can be in either direction. The cues assume a starboard (right) roll.

1. Achieve straight and level flight on a cardinal heading or section line at 350 KIAS and an altitude where a projection of the airplane’s flight path ahead 10 miles will not intersect the terrain. Choose an even thousand-foot altitude (1000, 2000, &c.)

2. Raise the nose of the aircraft 5-10o above the horizon (a gentle climb results) and—without hesitating—initiate a smart roll to the inverted position at a roll rate not less than 60o per second. That is, you should reach the inverted position in not more than 3 seconds.

3. As you roll, release backpressure on the sick to avoid turning; your heading must remain unchanged. The nose will begin dropping toward the horizon. At 90o of bank, the G force will be zero, and the nose should be dropping close to the horizon; the altimeter will be decreasing toward your original altitude. The direction of the aircraft should not change. As the aircraft exceeds 90o of bank (past the vertical position), begin to apply forward stick to keep the nose from dropping below the horizon.

4. As you reach 180o of bank, apply enough forward stick to maintain a negative angle of attack sufficient to keep the inverted aircraft in level flight. (That is, the altimeter will return to and then not vary from your original altitude.) The G force on the aircraft will be –1.0 G.

5. Maintain altitude in straight and level inverted flight for 10-20 seconds.6. Now continue the roll to an upright position. To maintain level flight, decrease forward stick

pressure from 180o to 90o of bank, and increase aft stick pressure from 90o to 0o of bank. Note that this is the reverse of what you did while rolling inverted.

7. The nose of the aircraft may be slightly below the horizon when you return to upright straight and level flight. Adjust it accordingly to maintain your original altitude and heading.

Visual Cues for Starboard (Right Roll) to Inverted Flight

Phase Visual CuesLevel Flight Azimuth and elevation steady; nose on horizon.

5 – 10o Nose Up Horizon drops; azimuth steady.0o - 90o Bank Horizon shows rapid roll; nose falling toward horizon; azimuth steady.

90o - 180o Bank Horizon shows continuing roll; nose falling through horizon; azimuth steady.180o Bank Azimuth and elevation steady with nose on horizon in inverted flight.

180o – 90o Bank Horizon shows rapid right roll; nose dropping (horizon rising); azimuth steady.Level Flight Azimuth and elevation steady; nose on horizon.

Instrument Cues for Right Roll to Inverted Flight

Phase Instrument CuesLevel Flight AI = wings level flight; AS; DG, ALT, TI = steady; VSI = 0; G = 1.0.5o Nose Up AI = nose up; AS; DG steady; ALT, VSI climbing; G = 1.0.

0o - 90o Bank AI = right roll, nose falling; AS, DG steady, ALT, VSI decreasing climb; TI = right roll; G = 0.0 at 90o of bank.

90o - 180o Bank AI = right roll, nose rising; AS, DG = steady; ALT, VSI decreasing descent; TI = left roll; G < 0.0.

180o Bank AI = wings level flight; AS; DG, ALT = steady; VSI = 0; TI = no turn; G = -1.0.

180o – 90o Bank AI = right roll, nose rising inverted, nose falling upright; DG = cardinal heading, ALT decreasing; VSI < 0; TI = left turn inverted, right turn upright; -1.0<G< 1.0.

Level Flight AI = wings level flight; AS, DG, ALT = steady; VSI = 0; TI = no turn; G = 1.0


Aileron, 4-Point and 8-Point Roll Maneuvers

The aileron roll (sometime called a slow roll, depending on the roll rate) is performed exactly like the inverted flight maneuver, except that there is no pause in the inverted position. From an initial slightly nose high position, the nose falls as the roll proceeds, until after 360o of roll the nose is on the horizon with the aircraft at its original altitude. As the roll rate decreases, the initial nose up attitude must increase to avoid “scooping out” during the second half of the roll.

The 4-point roll is an aileron roll where the aircraft roll rate is halted momentarily after every 90o degrees of roll, i.e., at 90o, 180o, 270o, and 360o degrees of roll. Depending on the roll rate and duration of the pauses, it may be necessary to start with the nose more than 5-10o above the horizon.

The 8-point roll is an aileron roll where the roll rate is momentarily halted every 45o of roll, i.e., at 45o, 90o, 135o, … 270o, 315o, and 360o. An initial nose up attitude of 15o or more will probably be required. If the roll rate is too slow, the aircraft may complete the maneuver with the nose well below the horizon. The 8-point roll is quite difficult to perform on MFS 2002 because the aircraft is so sensitive to stick movement.

Visual Cues for Right Aileron Roll

Phase Visual Cues0o - 90o Bank Horizon shows right roll; nose falling; azimuth steady.

90o - 180o Bank Horizon shows roll; nose falling; azimuth steady.180o – 90o Bank Horizon shows roll; nose falling; azimuth steady.90o – 0o Bank Horizon shows roll; nose falling to steady on horizon; azimuth steady.

Instrument Cues for Right Roll to Inverted Flight

Phase Instrument Cues

0o - 90o Bank AI = right roll, nose falling; AS, DG steady, ALT, VSI decreasing climb; TI = right roll; G = 0.0 at 90o of bank.

90o - 180o Bank AI = right roll, nose falling; AS, DG = steady; ALT, VSI descent; TI = left roll; G = -1.0 at 180o of bank

180o – 90o Bank AI = right roll, nose falling; AS; DG = steady; ALT, VSI = descent; TI = left roll G = 0.0 at 90o of bank.

90o – 0o Bank AI = right roll, nose falling; AS, DG = steady, ALT, VSI = descent; TI = right roll; G = 1.0 at 0o bank; AI = steady on horizon, ALT, VSI = 0 at end of roll.


Wingover Maneuver

The wingover maneuver involves an 180o turn coordinated with a climb and subsequent descent to the original altitude. After 45o of turn, the bank angle is 45o, the nose is 15-30o above the horizon, and the aircraft is climbing. After 90o of turn, the bank angle is 90o and the nose is falling through the horizon. At this precise moment, the VSI momentarily shows zero. The aircraft is at its maximum altitude and is neither climbing nor descending. After 135o of turn, the bank angle is 45o, the nose is 15-30o below the horizon, and the aircraft is descending. After 180o of turn, the aircraft is straight and level at its original altitude on a heading reciprocal to its original heading.

Pilot Procedures. The turn can be in either direction. The cues assume a port (left) turn.


2. Initiate a climbing turn such that after 45o of turn, the bank angle is 45o and the pitch angle is 15-30o nose up. Here and throughout roll rate should remain constant, though roll direction changes at step four.

3. Gradually release stick backpressure without changing roll rate so that after 90o of turn the bank angle is 90o and the nose of the aircraft is on the horizon (pitch angle = 0).

4. Reverse the roll direction as the nose falls through the horizon so that as the aircraft reaches 135o of turn, the bank angle is again 45o and the pitch angle is 15-30o nose down.

5. Increase stick backpressure to arrest the rate of descent and arrive at your original altitude and airspeed when 180o of turn is reached. The aircraft is now in straight and level flight on a heading reciprocal to your original heading.

Visual Cues for Wingover Maneuver with Left Turn

Phase Visual Cues0o - 45o of Turn Horizon shows nose rising and left roll to 45o left wing down.45o - 90o of Turn Horizon shows nose falling to horizon and left roll to 90o bank.

90o – 135o of Turn Horizon shows nose falling and right roll to 45o left wing down.135o – 180o of Turn Horizon shows nose rising to horizon and right roll to 0o bank.

Instrument Cues for Wingover Maneuver with Left Turn


0o - 45o of Turn AI = left roll, increasing nose up pitch; AS = decreasing; DG = counter-clockwise turn, ALT increasing; VSI increasing climb; TI = left turn; G = 1.0.

45o - 90o of Turn AI = left roll, decreasing nose up pitch; AS = decreasing; DG = counter-clockwise turn, ALT = increasing; VSI decreasing climb; TI = left turn; G =1.0.

90o – 135o of Turn AI = right roll, increasing nose down pitch; AS = increasing; DG = counter-clockwise turn, ALT = decreasing; VSI = increasing descent; TI = left turn; G =1.0.

135o – 180o of Turn AI = right roll, decreasing nose down pitch; AS = increasing; DG = counter-clockwise turn, ALT decreasing; VSI = decreasing descent; TI = left turn; G = 1.0.


Barrel Roll Maneuver

The barrel roll effects a 360o roll around an imaginary horizontal cylinder (barrel) such that the heading during the maneuver is constantly changing, yet the aircraft ends up on its original heading, altitude, and airspeed. From upright straight and level flight, a climbing roll is initiated, resulting in a climbing turn. The roll rate should be constant throughout the maneuver. At the inverted position, the nose has fallen through to the horizon and the direction of turn (but NOT the direction of roll) reverses. During the second 180o of roll, the nose drops below the horizon and then returns to the horizon as level upright flight is achieved. Imagine the aircraft’s original position and flight path to be along the axis of the cylinder.

The change of heading in this maneuver varies between 45o and 90o depending on the roll rate. For slower roll rates, a higher maximum nose up position is required to avoid “scooping out” during the second half of the maneuver. A roll rate that results in 45o maximum heading change is achieved by using a maximum nose up pitch of 30o. If you use 45o maximum pitch with a slower roll rate, the maximum heading change should be about 90o. For faster roll rates, the maximum pitch angle should be decreased; this results in a maximum change of heading less than 45o and a decreased altitude gain and loss. As you increase roll rate and “tighten” your roll diameter, you approach an aileron roll, where a rapid roll rate results in no heading change.

Pilot Procedures. The roll can be in either direction. The cues assume a port (left) roll.


2. Start a 3.5 G pull up, together with a left roll, to achieve 90o of roll by the time the nose has reached a maximum nose pitch angle of 30o. G decreases slightly as the airspeed decreases.

3. Continue the constant left rate roll with back stick pressure sufficient to pull the nose through to the horizon by the time the inverted position is reached. The G force will be 1.5 to 2.0. Heading at this point should have changed by 45o counterclockwise.

4. Continue the left roll to 90o right wing down as the nose falls below the horizon 30o. Increase G gradually. As soon as the right wing drops below the horizon at positive G, the turn direction will change from counterclockwise to clockwise.

5. Start the nose up, continuing the left roll, to achieve straight and level flight at the original altitude and airspeed on the original heading. Maximum G in the pull-up will be about +3.5.

Visual Cues for Barrel Roll Maneuver with Left Roll

Phase Visual Cues0o - 90o of Roll Horizon shows nose rising, left roll to 90o left wing down. (A/C turning left.)

90o -180o of Roll Horizon shows nose falling, left roll to inverted flight. (A/C turning left.)180o –270o of Roll Horizon shows nose rising, left roll to 90o right wing down. (A/C turning right.)270o – 360o of Roll Horizon shows nose rising, left roll to level flight. (A/C turning rights.)

Instrument Cues for Barrel Roll Maneuver with Left Roll


0o - 90o of Roll AI = left roll, increasing nose up pitch; AS = decreasing; DG = counterclockwise turn, ALT increasing; VSI increasing climb; TI = left turn; G = 3.5 decreasing.

90o -180o of Roll AI = left roll, decreasing nose up pitch; AS = decreasing; DG = counterclockwise turn, ALT = increasing; VSI decreasing climb; TI = left turn; G =2.0 – 1.0.

180o –270o of Roll AI = left roll, increasing nose down pitch; AS = increasing; DG = clockwise, ALT = decreasing; VSI = increasing descent; TI = right turn; G =1.0 – 2.0.

270o – 360o of RollAI = left roll, decreasing nose down pitch; AS = increasing; DG = counter-clockwise, ALT decreasing; VSI = decreasing descent; TI = left turn; G = 2.0 - 3.5, decreasing abruptly to 1.0 in straight and level flight.


Loop Maneuver

The loop is conceptually among the simplest of all aerobatic maneuvers, though it is easy to get off heading during the portion of the flight where you lose sight of the horizon due to limited visibility from the cockpit. Simply stated, a loop is a 360o wings level vertical turn executed in a plane. (If your bank angle ever varies from wings “level,” you will quickly stray from this plane.) The aircraft starts and finishes in upright straight and level flight at the original altitude and airspeed, on the original heading.

From the starting position, pull up smartly at 4 to 5 Gs, increasing back stick as the airspeed slows to keep significant positive G on the airplane. As the aircraft passes 90o nose up, the AI “flips” and the DG reverses to the reciprocal heading. Inverted with the nose on the horizon, G drops to about +2.0-2.5. The second half of the loop is the inverse of the first half. At 90o nose down the AI again flips ad the DG reverses again, to the original heading if you have stayed faithfully in the vertical plane. Pullout to achieve the original altitude and airspeed will again require a G force of 4 to 5. If you don’t decrease G force in the top half of the loop, your flight path will describe an ellipse instead of a circle, because airspeed slows at the top, and at a fixed G, a low airspeed results in a more rapid rate of vertical turn than a high airspeeds.

Pilot Procedures.

1. Achieve straight and level flight on a cardinal heading or section line at 400-450 KIAS and an altitude where a projection of the airplane’s flight path ahead 10 miles will not intersect the terrain. Choose an even thousand-foot altitude (1000, 2000, &c.)

2. Start a 4.5 G pull up. Bank angle must remain zero throughout the maneuver. Increase back stick pressure to keep positive G force on the aircraft. As you reach 90o nose up, the AI flips to show you are now inverted. G force is 3.0 – 3.5. Keep the stick backpressure on, and use the AI to be sure you don’t inadvertently enter a bank as you lose sight of the horizon. When the nose falls through the horizon, G force should be about 2.0. Airspeed is about 225 knots, altitude gain about 6000 feet.

3. The second half of the loop is the inverse of the first half. As you approach the 90o nose down position, G force should be about 3.5 – 4.0. As you approach wings level, G force should be 4 – 5 G. Level out at your original altitude and airspeed on your original heading.

Visual Cues for Loop Maneuver

Phase Visual Cues0o - 90o Vertical Turn Upright; nose rising from horizon; bank angle = 0; azimuth steady.

90o - 180o Vertical Turn Inverted; nose dropping toward horizon; bank angle = 0; azimuth steady.180 - 270o Vertical Turn Inverted; nose dropping below horizon; bank angle = 0; azimuth steady.270o – 360oVertical Turn Upright; nose rising toward horizon; bank angle = 0; azimuth steady.

Instrument Cues for Loop Maneuver


0o - 90o Vertical TurnAI = upright, increasing nose up pitch; bank angle zero; AS = decreasing; DG = steady; ALT = increasing; VSI increasing climb; TI = no turn; G = 4.5- 3.0; AI and DG “flip” at 90o nose up.

90o - 180o Vertical Turn AI = inverted, decreasing nose up pitch; bank angle zero; AS = decreasing; DG = steady on reciprocal of original heading; ALT = increasing; VSI decreasing climb; TI = no turn; G = 3.0 – 2.0.

180 - 270o Vertical TurnAI = inverted, increasing nose down pitch; bank angle zero; AS = increasing; DG = steady on reciprocal of original heading; ALT = decreasing; VSI decreasing climb; TI = no turn; G = 2.0 – 3.5.

270o – 360oVertical TurnAI = upright, decreasing nose down pitch; bank angle zero; AS = increasing; DG = steady; ALT = decreasing; VSI decreasing descent; TI = no turn; G = 3.0- 4.5; AI and DG “flip” at 90o nose down.


Half and Full Cuban Eights; Immelmann; Split S

The half Cuban eight begins as a loop. When the nose is 80-85o nose down inverted—almost three-quarters of the way through the loop—commence a smart 180o roll which must be complete as you reach the nose down vertical position. Now execute the last quarter of a loop, ending up at the original altitude and airspeed but on the reciprocal of the original heading.

The full Cuban eight is two half Cuban eights performed in succession without any intermediate delay. The aircraft ends on the original heading and airspeed at the original altitude.

The figure below shows vertical profiles for the loop and full Cuban eight maneuvers.

3 3 7

2 4 2 4 6

8 5 5 1 9 1

Vertical Profiles for Loop and Full Cuban Eight Maneuvers

An Immelmann—named after Max Immelmann (1890-1916), the WWI German ace who used the maneuver to trade airspeed for altitude in a dogfight—is nothing more than half a loop followed by a 180o roll to wings upright as the airplane reaches the top of the loop inverted. Airspeed at the completion of an Immelmann is much lower than at its inception.

The split S maneuver is the second half of a loop. From an altitude appropriate to your airspeed, roll inverted and “pull through” to level flight. It should be obvious that high initial airspeed will result in a much greater altitude loss than low initial airspeed. A common mistake in “pull throughs” in real airplanes is pulling too hard to avoid ground impact and overstressing or destroying the aircraft. Another is pulling hard enough at a low airspeed to induce an accelerated stall, which ensures that the aircraft’s nose cannot be raised further toward the horizon. The pictures on the course top web page illustrate this second mistake. The F8 shown crashing went into the clouds at the top of a loop and emerged at low airspeed with the nose near vertical. By pulling hard, the pilot reached an attitude where the nose was near the horizon; however, the airspeed was low, and at high G an accelerated stall occurred, followed by a post-stall departure. As the aircraft departed, it pitched 90o nose down at 1500’ AGL. This occurred during an air show aboard an aircraft carrier. The photo showing the F8 about to impact the water in a 90o dive was shot by an observer in vulture’s row in the carrier’s island structure.


Federal Aviation Regulations Pertaining to Aerobatic Flight

§ 91.303 Aerobatic flight.No person may operate an aircraft in aerobatic flight

a. Over any congested area of a city, town, or settlement;b. Over an open air assembly of persons;c. Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace

designated for an airport;d. Within 4 nautical miles of the center line of any Federal airway;e. Below an altitude of 1,500 feet above the surface; orf. When flight visibility is less than 3 statute miles.

For the purposes of this section, aerobatic flight means an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight.

[Doc. No. 18834, 54 FR 34308, Aug. 18, 1989, as amended by Amdt. 91-227, 56 FR 65661, Dec. 17, 1991]

To access this FAR on the web (among other FARs), go to:

http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr91_00.html, then click the 91.303 link.


http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr91_00.html

IV. UPSET AERODYNAMICS

Some—but not all—of the information presented in this section is a review of material covered in AS309 Basic Aerodynamics as taught at the Embry-Riddle Aeronautical University’s Daytona Beach campus. Since AS309 is prerequisite for AS495, you should already be familiar with much of what follows. AS310 Aircraft Performance also treats some of the material covered below.

If you would like to review course content in AS309 and/or AS310, visit the following web sites, where you can download course outlines, notes, and review notes for these two courses. Notes are in MSWord format.

http://faculty.erau.edu/rogersr/as309 http://faculty.erau.edu/rogersr/as310

Other prerequisite knowledge for what follows is taught in the two math courses required for Aeronautical Science majors, MA111 and MA112, and the two physics courses PS103 and PS104. All of these courses are either corequisite or prerequisite for AS309, hence required for AS310 and AS495 All Attitude Flight.

Standard Atmosphere Table

Average or standard values for atmospheric pressure P, temperature T, and density have been scientifically determined for various altitudes at and above mean sea level. A Standard Atmosphere Table lists these values for altitudes where aircraft normally operate. Po, To, o, and ao are respectively pressure, temperature, density, and the speed of sound at sea level in a standard atmosphere.

Some of the parameters reflected in a Standard Atmosphere Table besides P, T, and are:

Pressure Ratio = P/Po

Temperature Ratio = T/To (absolute temperature) Density Ratio = /o

Speed of Sound a = ao

The equation = / reflects an important quantitative relationship between pressure, temperature, and air density. Note that the speed of sound a in air is a function of temperature only, as implied by the equation a = ao .

Airspeeds

Definitions.

Indicated Airspeed (IAS) is the airspeed displayed on the airspeed indicator. Calibrated Airspeed (CAS) is IAS corrected for airspeed instrument error, i.e., pitot-static system

error. The correction is aircraft dependent. Equivalent Airspeed (EAS) is CAS corrected for air compressibility error. As CAS increases, air

begins to compress in the pitot tube, causing the airspeed indicator to read too high. The correction is aircraft independent, i.e., the same for every aircraft. Note that the following inequality holds: EAS CAS; i.e., the non-negative correction to obtain EAS from CAS is always subtracted from CAS.

True Airspeed (TAS) is EAS corrected for non-standard air density, and is a measure of the speed of the aircraft through its surrounding air mass. As altitude increases, air becomes less dense, and the airspeed indicator accordingly reads increasing lower than a fixed TAS. The correction from EAS to TAS can be made using the equation TAS = EAS / . Recall that is density ratio at the altitude where you are flying. Note that in a standard atmosphere at altitudes no lower than sea level, EAS is never larger than TAS.

Mach Number (M) is the ratio of TAS to the speed of sound where you are flying; i.e.,M = TAS / a = EAS / (a0 ).


http://faculty.db.erau.edu/rogersr/as310


As an example of the relationship between airspeeds, at 40,000 feet in a standard atmosphere, if calibrated airspeed is 328 KCAS, equivalent airspeed is 300 KEAS, and true airspeed is EAS / = 300 / 0.246177 = 604.65 KIAS. The Mach number is M = TAS / a = 604.65 / 573.80= 1.054. This can also be computed as M = EAS / (a0 ) = 300 / (661.74 0.18509) = 1.054. Since pitot-static system error is usually small, the indicated speed is about 328 KIAS. The plane at 40,000’ responds to controls as if it were flying at sea level at 300 KCAS = 300 KEAS = 300 KTAS. The navigator sees the plane as going 605 knots through its air mass.

Key Idea: A plane responds to control input according to its EAS; TAS is of interest mainly to navigators.

Static, Dynamic, and Total Pressure

Static pressure P is the pressure exerted by stationary air.

Dynamic Pressure q is pressure exerted by air against an object having relative motion through the air; quantitatively, q = V2/2, where is air density and V is TAS. It is easy to show that dynamic pressure against an airplane is a function of the square of equivalent airspeed, i.e., q (EAS)2.

Total pressure H is the sum of static and dynamic pressure. i.e., H = P + q.

Lift and Drag

When air flows across a wing, airflow velocity over one surface in most flight situations exceeds airflow velocity over the opposite surface. The difference in velocities is due to the wing’s camber and angle of attack. Since static pressure varies inversely with dynamic pressure according to Bernoulli’s principle, the wing surface with the higher airflow velocity has lower static pressure, resulting in a net aerodynamic force acting away from that surface. The component of this aerodynamic force perpendicular to the wing surface is known as lift.


L AF

D

relative wind

Angle of Attack. The angle of attack of a wing is the angle between the relative wind and the chord line of the wing. The coefficient of lift CL increases linearly with up to the point of stall, i.e., the point where the airflow begins to detach from the surface of the wing, then drops. The rate of decrease in CL is pronounced in a straight wing airplane, much less so in a swept wing airplane.

Stall. An airplane is stalled any time the wing reaches the critical angle of attack (crit). This stall is sometimes referred to as low speed stall to distinguish it from high speed or Mach stall. However, the airspeed for crit need not be low: if an airplane is developing a high G force, it can stall at relatively high airspeeds, because a high AOA is required to generate the high lift which increases the G force (discussed below).

Mach Stall. As an airplane approaches Mach 1.0, shock waves begin to develop on the airframe, especially on the wings. At Mcrit, usually about 0.88 – 0.90 Mach in an airliner, the AF moves aft on the wings, creating a nose down pitch, which can cause airspeed increase. It can be very difficult to get the nose back above the horizon. We will mention mach stall again when we discuss the airspeed operating envelope.

Lift Equation. The lift equation is , where CL is the coefficient of lift, is

the density ratio of the surrounding air, V is the TAS in knots, and S is the planform area of the wing in square feet. (The second equation follows from the first because V2 = (TAS)2 = (EAS)2.) That is, for fixed configuration (constant S), lift increases as angle of attack, air density, or airspeed increases. The effects on lift of changing these parameters independently may be summarized as follows:

At constant altitude, airspeed, and configuration, increasing angle of attack on an unstalled wing increases lift.

At constant altitude and configuration, increasing EAS (or IAS) increases lift. At constant TAS and configuration, decreasing altitude in a standard atmosphere increases lift

because air density increases. At constant EAS and configuration, but regardless of altitude, changing angle of attack is the only

way to change lift.

Drag. Drag falls into two categories, induced and parasite. Parasite drag is due to dynamic pressure and increase according to V2 /2 i.e., proportional to the square of TAS at constant density altitude, and proportional to the square of EAS regardless of altitude. Induced drag results from wingtip vortices generated while creating lift. At high angles of attack, induced drag is high, while induced drag decreases as angle of attack decreases. In the drag equation, given below, CD is the coefficient of drag. Its value depends both the induced and parasitic coefficients of drag.


Total Drag and Thrust Required Curves. In steady state flight, as airspeed increases induced drag decreases and parasite drag increases, as shown in the example below of a total drag (DT) curve. This curve is the same as the thrust required, since TR = DT (approximately) in steady state constant altitude wings level flight. Both curves are for a given aircraft at 1 G in fixed configuration at fixed altitude, airspeed, and gross weight.

T38 Total Drag Curve SL 10,000# Gross T38 Thrust Required Curve SL 10,000# Gross

Back Side of the Thrust Curve. The ratio L / D is called the lift-drag ratio. In steady state wings-level constant altitude flight below the airspeed for (L/D)max, more thrust is required to maintain a lower airspeed due to the large increase in induced drag when the AOA increases as the aircraft is slowed. This region is called the region of reversed command. (See illustration below.)

Airspeed need not be low to develop high induced drag. If an airplane is in high G maneuvering flight, it will develop high induced drag. In the extreme, the drag may be so great that thrust cannot overcome it. Loss of airspeed, increased AOA, and stall can ensue rapidly. In a nose-down airliner at modest IAS with the yoke full back, the resulting high AOA can create so much induced drag that the airspeed will not increase even when the nose falls well below the horizon. An accelerated stall develops, and the dive continues. To recover, a pilot must release yoke back pressure and let the airplane accelerate to flying speed, then reapply back yoke raise the nose above the horizon. This is hard to do when you see ground coming up rapidly in the windscreen.


Lift on the Lower Surface of the Wing. The aerodynamic force vector normally acts away from the upper surface of the wing. However, in sustained inverted flight, the aerodynamic force acts away from the lower surface of the wing. Here the terms “upper” and “lower” refer to the wing surfaces relative to the pilot’s orientation in the cockpit, not relative to the horizon or ground. When lift is being produced from the wing’s lower surface, the aircraft is in negative G flight. (See below for a definition of G force and a more thorough development of this idea.)

Turning Flight and G Force

Lift Vector and Turn Direction. In constant altitude turning flight at constant airspeed, the lift vector must increase, since only the vertical component of lift supports the weight of the aircraft. The horizontal component of lift is the unbalanced force causing radial acceleration toward the center of turn. As bank angle increases, L must increase inversely with cos , where is the bank angle.

As illustrated below, an aircraft always turns in the direction of the lift vector. Naively stated, this idea says that an airplane follows its lift vector. This is an important consideration in recovery from nose low upsets. Since any bank angle results in a turn, first roll the shortest direction to the wings level upright position. This points the lift vector toward the sky. Then raise the nose above the horizon. If you try to pull up the nose while in a bank, you must develop more lift than when you are level, since some of the lift will be used to turn. If you apply maximum lift (up to crit, or up to maximum allowable G), then the nose won’t come up as quickly as it would if the wings were level.

Upright Constant Altitude Positive G Flight Right Wing

Down: Clockwise Turn(Turn is to Pilot’ Right)

Inverted Constant Altitude Negative G Flight Right Wing Down: Counterclockwise Turn

(Turn is to Pilot’s Right)

Inverted Constant Altitude Negative G Flight Left Wing

Down: Clockwise Turn(Turn is to Pilot’s Left)

G Force (Load Factor). The G force developed by an airplane is by definition the lift developed by the aircraft divided by the weight of the aircraft: if the aircraft is in a constant altitude constant airspeed turn at bank angle , then since L cos = W

G = L / W = L / (L cos ) = 1 / cos .

If = 45o in the illustrations above, then G = 1 / cos 45 = 1.4 G. In the left picture, the G is +1.4. In the two right pictures, the airplane is developing –1.4 G.

Since cos 90o = 0, the G equation implies infinite G (infinite lift) is required to maintain a bank angle of 90o

in a level turn, which is obviously impossible. In fact, it is difficult to sustain constant bank, constant altitude, constant airspeed turns in any airplane at much more than 80o bank, and most airplanes develop so much induced drag at much lower bank angles that loss of airspeed and/or an accelerated stall results.

It is easy to show that for G > 0,stall speed VS increases by G; e.g., at +4.0 G, VS doubles (4 = 2).


L cos

W

L

L sin

L cos

W

L

L sin

L cos

W

L

L sin

Stability

Types of Stability. Consider the behavior of a moving object where all forces acting on it are balanced. According to Newton’s Law of Inertia, the object will remain in motion at a fixed velocity. If an outside force—for example a wind gust on an airplane in flight—displaces the object, the subsequent behavior of the object defines the stability of the system. The initial behavior of the object determines its static stability. As illustrated below, if the object returns toward its original position, it possesses positive static stability. If it stays in its displaced position, it possesses neutral static stability. If it moves further from its original position, it possesses negative static stability.

Positive (Stable), Negative (Unstable) and Neutral Static Stability Illustrated

If and only if an object possesses positive static stability, it also possesses positive, neutral, or negative dynamic stability. As the object initially returns toward its original position, oscillations begin. If the oscillations damp out, the object has positive dynamic stability. If the oscillations increase in amplitude, the object has negative dynamic stability. If the oscillations neither decrease nor increase, the object has neutral dynamic stability.

Airplane Controllability/Stability Axes

As illustrated above, controls allow a pilot to rotate an airplane around its three axes. Rotation around the lateral axis is known as pitch. Rotation around the longitudinal axis is known as roll. Rotation around the vertical axis—perhaps more accurately known as the directional axis, since it is not always “vertical”—is known as yaw. One speaks of the pitch, roll, and yaw (or directional) stability of an airplane. Stability and controllability are in one sense—but surely not in every sense—antithetical concepts. For example, an airplane with strong positive roll stability may have a slow roll rate (the high-wing C-172 is an excellent example). Conversely, military swept-wing fighter/attack type aircraft with high roll rates often have neutral or negative static roll stability; i.e., if a wing drops during an instrument approach while the pilot’s attention is distracted from the instrument panel, the wing may not start back up; indeed, it may continue to


drop until the pilot notices the event and initiates remedial action. Lack of positive roll stability is the price aircraft designers pay to obtain the potentially high roll rates desirable in military high-performance aircraft.

Airliners typically possess positive static stability around all three axes; i.e., have positive static pitch, roll, and yaw stability. Instability with respect to roll and pitch are dangerous situation. However, pitch stability can be adversely affected by exceeding aft-CG limitations. Yaw instability resulting in “end-swapping” in high performance military swept-wing aircraft has been experienced at high mach numbers; this phenomenon can be countered by installing a computerized yaw stability system and/or by the addition of ventral fins which perform a duty similar to the vertical stabilizer.

What follows contains additional information about airplane stability/controllability. See the AS309 Notes Unit III (http://faculty.erau.edu/rogersr/as309) for more detailed information about airplane stability.

Pitch Control

Flying Tail vs. Elevator. High performance military jets typically have no elevator. They achieve both pitch control and pitch trim by moving the entire horizontal stabilizer, called a unit horizontal tail, flying tail, or stabilator. The result is very sensitive pitch control, ordinarily an advantage. However, dangers are inherent in this system at high q flight, i.e., during flight at high IASs. First, pulling back too hard on the stick can create very high G forces which exceed design limitations, overstressing the aircraft and in some instances leading to wing spar failure and disintegration of the aircraft. Second, very sensitive pitch control can lead to the pilot’s control stick inputs getting out of phase with the actual pitch movements of the airplane. The result is PIO—Pilot Induced Oscillation—which, although infrequently encountered, can quickly lead to destruction of an aircraft. (Recovery from PIO is effected by letting go of the control stick, allowing the aircraft’s inherent stability to damp out undesired high-frequency pitch oscillations.)

Jet airliners and transports, by contrast, use an elevator to effect pitch control. However, unlike the situation on GA airplanes, there is no elevator trim tab. Instead, the entire horizontal stabilizer is repositioned to trim pitch moments to zero. This design—like the flying tail—also has its drawbacks. Runaway nose up or nose down trim can create a pitch situation where horizontal stabilizer movement “overpowers” the pitch commands of the relatively small elevator. For example, with runaway nose up trim (horizontal stabilizer leading edge in the full down position), full forward deflection of the control yoke (full down deflection of the elevator) will probably not effectively counter the rapid nose up pitch of the airplane, especially at high IASs. Unless the runaway trim can be remedied, loss of control can ensue.

Primary vs. Secondary Flight Controls. Ailerons & spoilers, rudder, and elevator are primary flight control surfaces. Secondary flight controls include engines, which affect pitch when mounted below or above the centerline, and yaw when thrust is applied differentially; speed brakes (spoilers), which induce pitch when deployed; and the horizontal stabilizer, which can be retrimmed to induce pitch moments.

Effect of CG on Stick Force Per Knot. You learned in AS309 that an airplane with static stability, when displaced from its trimmed attitude, begins to move back to that trimmed attitude. For example, if the nose pitches up with the aircraft trimmed for straight and level flight, evidence of positive static longitudinal stability is that the nose begins to move back down toward the horizon. If the resulting phugoid (low frequency) pitch oscillations ultimately damp out, the airplane also has positive dynamic longitudinal stability.

From the above observation, we may conclude that yoke force is required to hold an airliner in level flight at an airspeed for which it is not trimmed. The force required to maintain the untrimmed airspeed is known as stick force per knot. Consider the following example: an airliner is trimmed for 250 KIAS in straight and level flight. If airspeed drops below 250 KIAS, the nose tries to pitch down (to maintain airspeed) and back yoke (pull force) is required to maintain level flight. Conversely, at airspeeds above 250 KIAS, the nose pitches up, and forward yoke (push force) is required to avoid climbing.



An interesting characteristic of airliners is that stick force per knot decreases as center of gravity (CG) moves aft toward the aerodynamic center (AC) of the airplane. Another way of saying this is that is easier to over control the airplane with respect to pitch if the CG shifts aft. This fact is reflected in the figure shown below, reprinted from the United Airlines Advanced Maneuvers Program Study/Reference Guide.

Required Yoke Force to Hold Out of Trim Airspeed as CG Changes

Maneuvering Stability. Related to static longitudinal stability, maneuvering stability (as defined in United Airline’s Advanced Maneuvers Program Study/Reference Guide) is a measure of the longitudinal stability of an airplane in other than 1 G flight. From the flight crew’s point of view, it is the yoke force necessary to maintain a certain G force or load factor. The measurement—comparable to stick force per knot—is called stick force per G.

RSS (Reduced Static Stability) Airplanes. Locating the CG well forward of the AC promotes static longitudinal stability. However, it also creates a nose-down pitching moment due to lift that must be countered by downward lift on the horizontal stabilizer. This downward lift on the tail increases the effective weight of the airplane, making it necessary to increase lift, which also increases induced drag. The result is decreased fuel efficiency and range.

To counter this problem, engineers have conceived the reduced static (longitudinal) stability airplane design. By moving the CG aft almost to the AC, the downward pitching moment due to lift is minimized, and a much smaller downward force is required on the horizontal tail. This design increases fuel efficiency and range significantly at the expense of having to deal with neutral or slightly negative static longitudinal stability.

The absence of positive static longitudinal stability in RSS airplanes is countered by the use of flight control computers controlling a stability augmentation system. Stability augmentation in fly-by-wire airplanes is effected by having the computer apply immediate elevator deflection to counter small uncalled changes in pitch attitude. If stability augmentation is inoperative, then airplane maneuvers must be restricted. FAR Part 25 requires that RSS airplanes have handling characteristics that permit safe flight and landing after a failure of the stability augmentation system.

Effect of Altitude on Stick Force per G. Maneuvering stability or stick-force per g is influenced by CG in the manner that stick force per knot is influenced: aft movement of the CG decreases stick force per G.

In addition, when the CG is near the AC—i.e, especially in RSS aircraft—stick force per G at constant IAS decreases with altitude due to reduced aerodynamic damping of the horizontal tail. A detailed explanation of this phenomenon is beyond the scope of the course, and indeed the discussion of the subject in United’s Advanced Maneuvers Program is less than completely clear on the subject. (The same material is available on the Boeing Web Site, and is likewise less than completely clear.)


Currently we are trying to find out more about this ostensible phenomenon. What is clearly true is that at the same EAS, vertical speed at fixed climb angle is much larger at altitude than at sea level, since TAS is much larger at altitude. For example, at 250 KEAS = 250 KTAS at sea level, a 2o climb angle results in a vertical speed of 884 fpm. At 35,000’, the same climb angle and EAS gives a vertical speed of 1587 fpm (since the TAS is EAS * SMOEFL350 = 250 [1.7964] = 449 KTAS).

Note: the vertical speeds discussed in the previous paragraph may be calculated as follows. The vertical speed in knots is given by KTAS sin a, where a is the climb angle and KTAS is of course the true airspeed. Then convert the resultant vertical speed in knots to fpm by multiplying by (6076 ft/nm / 60 min/hour.) Thus, 250 sin 2 (6076/60) = 883.5389248 fpm gives the vertical speed for a climb angle of 2o at sea level and 250 KEAS = 250 KTAS. The vertical speed at 250 KEAS at 35,000’ is calculated in a similar manner:SMOEFL350 (sin 2) (6076/60). A quicker way is to multiply SMOEFL350 times the vertical speed at sea level, i.e., times 883.5389248, giving 1587.189325 fpm.

It follows from the above discussion is that changes in vertical speed for a given control input will be greater at high altitude than at lower altitudes. In short, an airliner is more sensitive to control pitch input at high altitude than at low altitude, i.e., is more easily over controlled.

The figure below—taken from United’s Advanced Maneuvering Program Manual—illustrates the effect of CG and altitude on stick force per G. (Again, the same material is available from Boeing.) The friction breakout force F0 is the force that must be applied to the yoke to overcome control column friction and control surface simulated feedback forces. The lower stick force at higher altitudes is due to the fact that—for the same EAS—the horizontal stabilizer when the nose is displaced from straight and level flight has a lower angle of attack and hence a lower damping force at high altitudes than at low altitude. This is due to the increasing difference between TAS and EAS as altitude increases.

Changes in Stick Force per Gs for Fixed Airspeed as CG and Altitude Vary

Key Idea Restated. Airliners are more sensitive to pitch control input at aft CG or at high altitude, compared to the responses that may be customary at forward CG and lower altitudes. Care must be exercised to avoid over controlling with respect to pitch under these circumstances.


Lateral Control

Dihedral Effect. There are several factors which promote static lateral stability in an airplane. These are discussed in detail in AS309 Aerodynamics. For more detail on what follows, see online notes on this subject (URL at beginning of this section).When a wing drops unexpectedly in level flight, sideslip into that wing is created. Factors which cause to aircraft to return toward level flight are:

Sweepback: the wing into a sideslip has more chord wise flow and more lift than the wing away from a sideslip. Thus the wing into the sideslip (down wing)) tends to rise and restore level flight.

Dihedral: the wing into a sideslip (down wing) has a higher angle of attack and more lift than the wing away from a sideslip. Thus the down wing tends to rise and restore level flight.

Both of the above phenomena are often referred to collectively as dihedral effect in airline manuals. In AS309 we use the term “dihedral effect” to describe the second phenomenon, and the phrase “dihedral effect of sweepback” to describe the first.

Ailerons and Spoilers. Most airliners use a combination of ailerons and spoilers to induce a rolling moment. A down aileron increases wing camber and lift, whereas an up aileron decreases wing camber and lift. An up spoiler reduces a wing’s lift by “spoiling” the boundary layer on its upper surface.

From the foregoing, it follows that if an airplane wishes to roll (and bank) for example to the right, a clockwise rotation of the yoke results in the aileron on the left wing moving down, the aileron on the right wing moving up, and the spoiler on the right wing moving up.

Effect of Low IAS on Roll Effectiveness. An aileron in the down position on a wing increases lift but decreases the critical angle of attack of that wing. Thus an airplane flying near the stall attempting to roll using aileron may find the airplane behaving precisely opposite to what is anticipated. For example, if you are close to a stall and command a smart right roll, the aileron drops on the left wing, decreasing the critical angle of attack and inducing a stall. (See the figure below, from United’s Advanced Maneuvering Program Manual.) At the same time, drag on the wing increases. The result at best is no response to the control input. More typically, the airplane will yaw and roll left and may enter uncontrolled flight. Loss of control is more likely in a swept wing than a straight wing airplane.

Compared to aileron input near the stall, use of spoilers alone is not as likely to result in uncontrolled flight. However, if you command for example a left roll with spoilers only near the stall, the left wing will stall while drag increases, perhaps resulting in a left yaw. This increases lift on the right (advancing) wing. The result can be that the airplane snap rolls to the left to a higher bank angle than anticipated, perhaps even near to or beyond the vertical.

Key Idea. Roll authority using wing control surfaces is severely compromised at or very near a stall. This is true whether the stall is a 1 G stall or accelerated stall. To regain roll capability, decrease the angle of attack by unloading the airplane. In an accelerated stall, use of ailerons can and not infrequently does lead to loss of control and an unexpected attitude.


Effect of Aileron Deflection on Critical Angle of Attack

Yaw/Directional Control

Ordinarily rudder is not needed in operating a swept wing jet airliner. However, airliners have large rudders capable of exerting powerful yaw forces on the airplane, since asymmetrical thrust after an engine failure can be severe, and must be capable of being overcome by rudder deflection.

Increasingly the airline industry is becoming aware of the fact that large, abrupt rudder movements can overstress and airplane. The crash of an American Airlines Airbus in Fall 2002 on Long Island appears to have been caused by abrupt rudder movement applied in an attempt to overcome yaw and roll apparently induced by wingtip vortices from a nearby heavy airplane. While the NTSB report is not complete, the press has reported that the rudder went through an abrupt and rapid cycle from full deflection in one direction to full deflection in the other. This would have produced rapidly changing severe yawing moments that may have been responsible for an engine’s breaking loose from the airplane in flight.

An important fact to remember is that yaw induces roll by causing the relative wind over one wing to be larger than over the other, leading to asymmetrical lift and a rolling moment. For example, in straight and level flight, application of right rudder causes a right yaw. The left (advancing) wing produces more lift than the right (retreating) wing, causing a roll to the right.

Key Idea. At angles of attack near the stall, aileron/spoiler application becomes increasingly ineffective to create a rolling moment. Yaw (rudder) can and should be used to roll the airplane in such circumstances if it is impossible or inadvisable to unload the airplane to decrease angle of attack.

Key Idea. A corollary to this idea is that especially at low IAS, roll is almost always more effective if rudder is used in coordination with aileron. (Howell and Rogers saw a vivid illustration of this fact when they flew the MD-11 simulator at Delta Airlines while undergoing upset training.) Just remember to apply the rudder smoothly and with discretion to avoid severe and/or rapid yaw that might subject the airplane to side loading forces which could cause structural damage. There seems to be little or no evidence that full deflection of the rudder in a single direction, if applied slowly at airspeeds within operating limitations, will cause structural damage. Rather, it is rapid cycling of the rudder pedals that seems to have been one of the culprits in the breakup of the American Airlines Airbus in New York.

Rudder Crossover Speed. This is the speed above which, assuming full uncalled rudder deflection, full opposed aileron/spoiler input will be sufficient to counter the resultant roll. For example, if the rudder deflects full right, a right roll results. Above the rudder crossover speed, rotating the yoke full counterclockwise will provide control input sufficient to stop the right roll and return to wings level flight. Compare VMCA, the minimum control speed in the air with the critical engine failed.


Load Factor and Aerodynamic Operating Limitations

Load Factor Envelope. Allowable G is a term referring to the permissible G a pilot may attain in an airplane. For an airliner, this is the load factor for which the airplane is certified. Airliners are certified for vertical load factors between –1.0 and +2.5. Ultimate G refers to the load factor beyond which structural damage including wing spar failure may be anticipated. Ultimate G for an airliner is about +4.0.

The load factor envelope for an airplane visually depicts allowable G as a function of airspeed. The maximum G because of structural limitations may not be achievable for low airspeeds because a stall (1 G or accelerated) occurs first. A load factor envelope (or load factor diagram) is often called a V-n diagram where V refers to airspeed and n stands for the number of Gs allowed. Load factor envelopes are for a specific aircraft at a specific altitude and gross weight.

Key Idea. If you command roll while developing high positive Gs, you subject one wing of your airplane to a greater load factor than the other. The “average” G force as measured along the centerline of the airplane will be more than the G force on the wing into the direction of the roll, and less than the wing away from the roll direction. In recovering from nose low upsets, rolling pullouts are rarely advisable for two reasons. First, the allowable G on the airplane is reduced in a rolling pullout. Second, in a rolling pullout the lift vector is increased before it is pointed “away” from the earth’s surface, i.e., before it has no lateral component perpendicular to the earth’s gravitational field. Thus part of the lift vector is being used to command roll or turn, reducing the component of lift available to raise the nose to the horizon, and delaying the return to straight and level flight.

Key Idea. In recovering from nose low upsets, first roll the in the nearest direction to level the wings in upright flight, eliminating any lift vector component which would command roll or turn. Then—after the wings are level—raise the nose to the horizon using back yoke.

The load factor diagrams shown below apply to specific airplanes in specific configurations at a specified density altitude and gross weight. They depict load factor envelopes for a typical airliner and a specific Navy fighter aircraft, the RF8G Photographic Reconnaissance version of the Ling-Temco-Vought Crusader. The rolling pullout limit for the RF8G is less than the allowable G pullouts involving only pitch attitude changes, since in a roll one wing develops more lift than the other, hence a greater load factor. The first diagram is from United’s Advanced Maneuvering Program Manual.

Load Factor Envelop (IAS vs. G force) for a Typical Airliner (Configuration, Gross Weight, and Density Altitude Fixed)


V-n Diagram (IAS vs. G force) for RF8G Photo Crusader (from RF8 NATOPS Flight Manual)

Aerodynamic Flight Envelope. Besides G limitations, an airplane is subject to airspeed limitations as follows:

VS – stall speed; the aircraft cannot be flown slower than this airspeed. VMO – maximum allowable operating airspeed because of structural limitations. MMO – airspeed corresponding to the maximum allowable Mach number for airplanes not designed

for flight into and beyond the transonic flight region. While pilots determine this speed using a Mach meter, plots of this value reflect the corresponding IAS or EAS.

VDF – maximum airspeed at which the airplane has been flown without incurring structural damage (DF = flight-demonstrated speed).

MDF – airspeed corresponding to the maximum Mach number at which the airplane has been flown while remaining controllable.

Operating range – difference between maximum and minimum allowable airspeeds.

Coffin Corner. The region where MMO = VS in an aerodynamic flight envelope is called the coffin corner. It is the point where the airspeed corresponding to the maximum Mach number is the same as the stall speed.

Key Idea. MMO is a critically important speed limitation in an airliner. Above MMO, the aircraft approach MCRIT, the critical Mach number, where compressibility effects lead to Mach stall (high speed stall) and an ensuing aft movement of the AC, causing a nose-down pitch. Once the nose gets below the horizon, the airplane—very clean with respect to drag—begins to accelerate rapidly and may enter the transonic region. Airspeed may not decrease even when thrust is reduced and spoilers (speed brakes) extended. Experience has shown that elevator alone may not be sufficient to raise the nose back to the horizon; pitch trim may be required, which can then lead to a nose high upset after the nose reaches the horizon.

An Aerodynamic Flight Envelope is aircraft, configuration, G force, and gross weight specific. In AS 310, Aircraft Performance, the envelope is depicted as shown below. Altitude is on the horizontal axis and EAS on the vertical axis.


Airspeed Envelop with 2G Safety Margin for Boeing 767 at 300,000# Gross

United’s Advanced Maneuvering Program Manual plots IAS on the horizontal axis and altitude on the vertical axis. Also, since flight near the coffin corner is highly inadvisable, the envelop neglects to depict that flight region.

Aerodynamic Flight Envelop for Typical Airliner (Airspeed is IAS)

Query. Can you explain why the stall speed IAS increases as altitude increases in the above figure, whereas the EAS stall speed in the immediately previous figure is constant?


Information from the Aerodynamic Flight Envelope—also called a Buffet Boundary Chart—is typically presented to pilots in tabular form, as illustrated below.

Maximum and Minimum B737 Airspeeds by Gross Weight with Changing Altitude

Another format for the buffet boundary chart is shown below, again from United’s Advanced Maneuvering Program Manual. The chart depicts information not available in table format, for example the effect of CG location and load factor on aerodynamic operating limitations.

Typical Buffet Boundary Chart for an Airliner


The chart shown above provides

Speed Margins from low-speed to high-speed (Mach induced) stalls at +1.0 G. Load factor (available G) and corresponding bank angle to buffet (accelerated stall) at different

Mach numbers. Altitude capability at a given Mach number and +1.0 G. (Can be interpreted as G available.)

As depicted below, the buffet boundary curves of different airplanes can vary in shape dramatically. For a given flight regime (mach number and altitude), the curves contains the following information:

Vertical distance to the curve reflects the altitude margin (which implies a G margin) Horizontal distance right reflects the high-speed margin (distance to Mach stall limit). Horizontal distance left reflects the low-speed margin (distance to low-speed stall).

Typical Buffet Boundary Curves for Different Aircraft

The shape of such a curve provides information about safety margins for a given flight condition, and implies strategies for recovering from upsets where speed and/or altitude changes may be large and rapid.

Corner Speed

Corner speed—sometimes called cornering speed—is the minimum airspeed at which maximum allowable positive G is available. Implicit in this definition is the idea that when maximum G is being developed at this minimum airspeed, angle of attack is such that maximum lift is being developed, i.e., at corner speed and maximum G the angle of attack is crit.


As illustrated in the above diagram—taken from a major airline pilot training manual—in recovering to level flight from a nose low attitude, corner speed allows a pullout at maximum allowable G with minimum loss of altitude. A lower speed than corner speed will result in more altitude loss since maximum G cannot be achieved before the airplane stalls. At a speed higher than corner speed, again more altitude will be lost since the airplane has higher kinetic energy but cannot avail itself of the G potentially available at the higher speed because of G limits imposed by the structural vulnerability of the aircraft.

Key idea: maintain corner speed and pull out at maximum allowable G to minimize altitude loss in recovering from a nose low attitude. (Avoid rolling pullouts, of course, which will increase the altitude loss by decreasing the allowable G force.)

Nothing in the above should be construed to say that you shouldn’t exceed the maximum allowable G of an airplane in pulling out of a dive if you otherwise will impact the terrain. It is better to risk pulling the wings off an airplane than to fly into the ground in a dive.

(Maximum allowable G in most airliners = +2.5, while ultimate positive G for most airliners is 4.0, so you have something like 1.0 – 1.5 discretionary G if you are about to fly into the ground in a nose low attitude. In military fighter/attack type aircraft, the discretionary G is even greater. But military pilots flying at high IASs have pulled the wings off their airplane by calling for more Gs than the wing spars can tolerate. It’s very easy to do: just pull back hard on the stick and die!

Use of Rudder in Airliner/Transport-Type Airplanes

NTSB Interim Safety Recommendation. The crash of American Airlines Flight 587 on Long Island in fall 2001 has precipitated an extensive inquiry into whether or not a pilot can overstress an airliner by the injudicious application of rudder. It appears that the PF on this flight initiated rapid rudder reversal in response to an upset caused by wingtip vortex disturbances from an airplane five miles ahead. The vertical fin and one engine departed the Airbus A300-600 airplane prior to uncontrolled ground impact. The accident report for Flight 587 is not yet complete. However, the NTSB has issued a safety recommendation based on information uncovered by the investigation to date. Both Boeing and Airbus Industrie have responded to the NTSB recommendation. Excerpts from the NTSB recommendation are given below. To see the full report, as well as Boeing’s and Airbus’s responses — among many other related documents—visit:

http://faculty.erau.edu/rogersr/as495/AA587

Sequential full opposite rudder inputs (sometimes colloquially referred to as “rudder reversals”)—even at speeds below the design maneuvering speed—may result in structural loads that exceed those addressed by [certification] requirements. (The design maneuvering airspeed is the maximum speed at which the structural design’s limit load can be imposed… without causing structural damage.)

Pilots may have the impression that the rudder limiter systems installed on most transport-category airplanes, which limit rudder travel as airspeed increases to prevent a single full rudder input from overloading the structure, also prevent sequential full opposite rudder deflections from damaging the structure. However, the structural certification requirements for transport-category airplanes do not take such maneuvers into account; therefore, such sequential opposite rudder inputs, even when a rudder limiter is in effect, can produce loads higher than those required for certification and that may exceed the structural capabilities of the aircraft.

Preliminary calculations by Safety Board and Airbus engineers show that large sideloads were likely present on the vertical stabilizer and rudder at the time they separated from the airplane. Calculations and simulations show that, at the time of the separation, the airplane was in an 8° to 10° airplane nose-left sideslip while the rudder was deflected 9.5° to the right. Airbus engineers have determined that this combination of local nose-left sideslip on the vertical stabilizer and right rudder deflection produced air loads on the vertical stabilizer that could exceed the airplane’s design loads. …[A]t the time the


http://faculty.erau.edu/rogersr/as495/AA587

vertical stabilizer and rudder separated from the airplane, the airplane was flying at 255 knots indicated airspeed (KIAS), which is significantly below the airplane’s design maneuvering speed of 273 KIAS.[Two paragraphs here describe the FAA certification standards for transport-category with respect to rudder deflection. These standards provide for full rudder deflection in unaccelerated flight with initial zero yaw and maintaining steady state sideslip angles resulting from this deflection. However, no provision is made for “rudder-cycling,” which results in yaw “over-swing,” i.e., yaw angles significantly in excess of what can be maintained by holding full rudder deflection in one direction. To quote from the report: “the airplane must be designed to withstand the results of a full rudder input in one direction followed by (after the airplane reaches equilibrium) a release of that rudder input.” However “certification requirements do not consider a return of the rudder to neutral from the over-swing sideslip angle, nor do they consider a full rudder movement in one direction followed by a movement in the opposite direction.

Although …most transport-category airplanes are equipped with rudder limiter systems that limit rudder deflection at higher airspeeds, which prevents single rudder inputs from causing structural overload, a full or nearly full rudder deflection in one direction followed by a full or nearly full rudder deflection in the other direction, even at speeds below the design maneuvering speed, can dramatically increase the risk of structural failure of the vertical stabilizer or the rudder.

Pilots may not be aware that, on some airplane types, full available rudder deflections can be achieved with small pedal movements and comparatively light pedal forces. In these airplanes, at low speeds (for example, on the runway during the early takeoff run or during flight control checks on the ground or simulator training) the rudder pedal forces required to obtain full available rudder may be two times greater and the rudder pedal movements required may be three times greater than those required to obtain full available rudder at higher airspeeds….Lacking an awareness of these differences in necessary pedal force and movement, some pilots, when sensing the need for a rudder input at high speeds, may use rudder pedal movements and pressures similar to those used during operations at lower airspeeds, potentially resulting in full available rudder deflection.4There is a potential for pilots to make large and/or sequential rudder inputs in response to unusual or emergency situations, such as an unusual attitude or upset, turbulence, or a hijacking or terrorist situation….The widely used Airplane Upset Recovery Training Aid, which was created by Airbus Industrie, the Boeing Company, many major domestic and international airlines, and major pilot organizations, states that, “pilots must be prepared to use full control authority, when necessary. The tendency is for pilots not to use full control authority because they rarely are required to do this. This habit must be overcome when recovering from severe upsets.”…Since the terrorist attacks of September 11, 2001, operators and pilots have been discussing ways to disable or incapacitate would-be hijackers in cockpits or in cabins during flight. Although [there exists a] need to formulate effective maneuvers for addressing such unusual or emergency situations,…without specific and appropriate training in such maneuvers, pilots could inadvertently create an even more dangerous situation if those maneuvers result in loads that approach or exceed the structural limits of the airplane.

Finally, notwithstanding the concerns noted above about the potential danger of large and/or sequential rudder inputs in flight, it should be emphasized that pilots should not become reluctant to command full rudder when required and when appropriate, such as during an engine failure shortly after takeoff or during strong or gusty crosswind takeoffs or landings. The instruction of proper rudder use in such conditions should remain intact but should also emphasize the differences between aircraft motion resulting from a single, large rudder input and that resulting from a series of full or nearly full opposite rudder inputs.


Boeing Response to NTSB Safety Recommendation. The last two and a half pages of Boeing’s response are too good and too succinct not to quote here. Note that the information on rudder use given below implicitly contradicts ideas found elsewhere in these notes and in other AS495L materials, some of which materials were produced earlier by Boeing.

Boeing recommends that:

Transport pilots should be made aware that certain prior experience or training in military, GA, or other non-transport aircraft that emphasizes use of rudder input as a means to maneuver in roll typically does not apply to transport aircraft or operations.

Transport pilots should be made aware that certain prior experience or training in military, GA, or other non-transport aircraft types emphasizing the acceptability of unrestricted dynamic control application typically does not apply to transport aircraft or operations. Excessive structural loads can be achieved if the aircraft is maneuvered significantly different than what is recommended by the manufacturer or the operator’s training program.

Finally, as background information, crews should “optionally” be able to learn more about their aircraft, such as how certain regulatory certification practices are accomplished. This could help them better understand what their aircraft have been tested for, the maneuvers their aircraft have been shown to be capable of safely doing, and conditions that have not specifically been tested.

For example, a manufacturer is required to demonstrate full stall and stall recovery characteristics. The FAA assesses whether the characteristics during a full stall are acceptable and that the recovery does not require any unusual pilot technique. Note that these stalls are not done in large dynamic yaw rate or sideslip conditions. Boeing airplanes have demonstrated entry and recovery from full stalls without the need for rudder. Boeing strongly recommends that the rudder not be used in a stall recovery, and that stall recovery should be accomplished before proceeding with any unusual attitude recovery. Once the stall recovery is complete, the ailerons/spoilers should provide adequate rolling moment for unusual attitude recovery. Unless a transport airplane has suffered significant loss of capability due to system or structural failure (such as a loss of a flap or thrust reverser deployment), rudder input is generally not required.

In simple pilot terms, if you are in a stall, don’t use the rudder; if you are not in a stall, you don’t need the rudder. The rudder in a large transport airplane is typically used for trim, engine failure, and crosswind takeoff and landing. Only under an extreme condition, such as loss of a flap, mid air collision, or where an airplane has pitched to a very high pitch attitude and a pushover or thrust change has already been unsuccessful, should careful rudder input in the direction of the desired roll be considered to induce a rolling maneuver to start the nose down or provide the desired bank angle. A rudder input is never the preferred initial response for events such as a wake vortex encounter, windshear encounter, or to reduce bank angle preceding an imminent stall recovery.

Finally, following the events of September 11, there has been much discussion about aggressively maneuvering the airplane to thwart a hijacking attempt. The Boeing recommendation in this situation has been to rely on maneuvers that do not apply inputs to the rudder. The issues discussed in this bulletin have shown the risks associated with large rudder inputs. The use of ailerons and elevators in this situation has limitations as well. Elevators and ailerons are not designed for abrupt reversalsfrom a fully displaced position. In all cases the manufacturer’s specific recommendations for aggressive maneuvering should be followed. Random unplanned maneuvers outside the manufacturer’s recommendations can lead to loss of control and/or structural damage.


Summary [from Boeing Response Document]

There has been no catastrophic structural failure of a Boeing airplane due to a pilot control input in over 40 years of commercial operations involving more than 300 million flights.

Jet transport airplanes have large and powerful rudders.

The use of full rudder for control of engine failures and crosswind takeoffs and landings is well within the structural capability of the airplane.

As the airplane flies faster, less rudder authority is required. Implementation of the rudder limiting function varies from model to model.

Airplanes are designed and tested based on certain assumptions about how pilots will use the rudder. These assumptions drive the FAA/JAA certification requirements and any additional Boeing design requirements.

The pilot should be aware that the airplane has been designed with the structural capability to accommodate a rapid and immediate rudder pedal input when going in one direction from zero input to full.

It is important to use the rudder in a manner that avoids unintended large sideslip angles and resulting excessive roll rates. The amount of roll rate that is generated by using the rudder is proportional to the amount of sideslip, NOT the amount of rudder input.

If the pilot reacts to an abrupt roll onset with a large rudder input in the opposite direction, the pilot can induce large amplitude oscillations. These large amplitude oscillations can generate loads that exceed the limit loads and possibly the ultimate loads, which could result in structural damage.

A full or nearly full authority rudder reversal as the airplane reaches an “over yaw” sideslip angle may be beyond the structural design limits of the airplane. There are no Boeing flight crew procedures that would require this type of rudder input.


V. AIRPLANE UPSET RECOVERY TECHNIQUES

Definition of Airplane Upset

An airplane upset—sometimes referred to as an unusual attitude—occurs when an airplane enters a flight regime prohibited by its operations or encounters an attitude unexpected by its pilot(s). Different airplane categories obviously require different definitions of the term upset. For example, a military fighter-type aircraft in an inverted nose low attitude is in its normal flight regime; the same attitude in an airliner definitely constitutes an upset, and in fact is a hair-raising experience that requires superior airmanship to overcome.

In the late 1990s, the Boeing Company in concert with Airbus and other industry participants, developed a definition of airliner upset that has been adopted by most carriers:

The four conditions that generally describe an airplane upset are unintentional Pitch attitude more than 25o nose up. Pitch attitude more than 10o nose down. Bank angle more than 45o. Flight within these parameters at airspeeds inappropriate for the conditions.

Energy States and Upset Recovery

Airplane Energy States. An airplane possesses three kinds of energy:

Kinetic: contributes to momentum; increases as the square of TAS Potential: due to the force of gravity acting on an airplane Chemical: burning fuel creates thrust

As illustrated below, kinetic energy can be converted to potential energy by climbing. This is called trading airspeed for altitude. Potential energy can be converted to kinetic energy by diving, which increases airspeed, i.e., by trading altitude for airspeed. Chemical energy becomes thrust which can be used to increase either kinetic energy or potential energy, i.e., used to increase airspeed or altitude respectively.

Relationships between Energy States in an Airplane Depicted Schematically

Energy States Related to Upset Recovery. Flying an airplane safely involves keeping kinetic energy within limits (VS to MMO, G within limits), while ensuring adequate potential energy (safe altitude) and sufficient chemical energy (fuel remaining).


In a very real sense, an upset occurs when an airplane is approaching or reaches an unsafe energy state. Recovering from an upset involves using primary and secondary flight controls to restore a safe energy states.

Naively stated, a nose high upset converts kinetic energy to potential energy. To recover, trade altitude for airspeed without stalling or overstressing the airplane.

A nose low upset converts potential energy to kinetic energy. To recover, trade airspeed for altitude without stalling or overstressing the airplane.

Upset Recovery Techniques for Fighter-Type Airplanes

G Force and Bank Angle. In an airliner or cargo-carrying airplane, steep bank angles and/or G forces less than 1.0 have a potentially negative impact on crew, passengers, and cargo alike. The same is not true of fighter type aircraft, since crewmembers are securely strapped into their seats, and cargo and passengers are nonexistent. Thus any useful bank angle or G force necessary to recover from an upset may be employed. (However, G forces less than 0.0 are rarely if every required.)

First Considerations. Before attempting to recovery from an upset, determine the attitude of the airplane. The attitude indicator is of course your primary instrument, but confirm what you see there by quickly correlating readings on the VSI, altimeter, and airspeed indicator, since the AI reading conceivably could be erroneous. Note thrust setting (RPM) since thrust must be adjusted according to whether the nose is above or below the horizon. If the aircraft is equipped with autopilot/autothrottle systems, ensure both are disengaged. Apply all your attention to recovering from the upset. After control is regained and straight and level flight achieved, you can begin to analyze what caused the upset. Above all, take time to think before acting. However, the thinking stage must proceed both quickly and accurately, since the airplane is out of control, and failure to act—like inappropriate control inputs—can and probably will make the situation worse rather than better.

Nose High Recovery. A nose high unusual attitude involves a situation where kinetic energy is being translated to potential energy. The altimeter is increasing, and the vertical speed indicator reflects a climb. Airspeed is decreasing. Of course the attitude indicator shows a nose position above the horizon.

Recovery is begun by rolling in the shortest direction toward a target bank angle of 90o, which will ultimately result in the nose falling toward the horizon. Only if the nose is close to the horizon when recovery begins will a bank angle less than 90o suffice. Ordinarily full thrust should be applied to maintain flying airspeed and increase altitude gain. Avoid applying positive Gs.

If airspeed is decreasing toward the 1 G stall speed, the roll to 90o of bank should be accomplished mainly with rudder, and at a G force not less than 0.0 but less than 1.0. After achieving 90o of bank, allow the aircraft’s nose to fall through to the horizon at a G force of approximately 0.0. As the nose approaches the horizon—assuming the airspeed is above the 1 G stall speed—roll in the shortest direction to wings level. If the airspeed is below flying airspeed, allow the nose to continue falling until stall speed is exceeded, then roll wings level. Avoid applying more than 1 G in the rollout. If airspeed is near the stall, rollout at less than 1 G using rudder as the primary control surface.

When a wings-level attitude is achieved, the nose will be somewhat below the horizon—probably between 10o and 30o nose down (hopefully ten and not thirty)—depending on airspeed when the nose reaches the horizon in a 90o bank. To complete the recovery, reduce thrust and raise the nose to the level flight position, being careful not to induce an accelerated stall. Remember not to try to roll wings level until you have appropriate flying airspeed.

Nose Low Recovery. A nose low attitude involves a situation where potential energy is being translated to kinetic energy. The altimeter is decreasing, and the vertical speed indicator reflects a descent. Airspeed is increasing, probably rapidly. The attitude indicator shows a nose position below the horizon. Depending on altitude AGL, ground impact is a deferred or immediate consideration.


Assuming that airspeed is above 1 G stall airspeed—which almost certainly will be the case—reduce thrust. If speed in increasing rapidly, you may wish to reduce thrust to idle RPM. Use speed brakes as required to keep airspeed under control. As soon as you have flying airspeed, smartly roll in the shortest direction to a wings level attitude. Use coordinated aileron/rudder to roll, and avoid putting more than 1G on the airplane.

This roll points the thrust vector away from the earth. You are now in a wings-level nose down attitude—probably the nose is significantly below the horizon. To complete the recovery, apply maximum safe and sustainable G to raise the nose to the horizon. As you approach the horizon, level off and adjust thrust to maintain level flight. Retract speed brakes if you previously extended them in the initial dive.


Summary of Recovery Techniques. The ideas on the previous page are summarized in the table below.

Nose High Recovery Nose Low Attitude1. Confirm nose high with instrument crosscheck2. Disengage autopilot and autothrottle3. Increase thrust as appropriate4. Roll in shortest direction to 90o bank angle5. As nose approaches horizon, roll to wings

level after flying airspeed is achieved6. Raise nose to the horizon and adjust thrust to

maintain level flight7. In steps 4 - 6, avoid stalling the airplane

1. Confirm nose low with instrument crosscheck2. Disengage autopilot and autothrottle3. Roll smartly in the shortest direction to wings

level4. Decrease thrust and extend speed brakes as

appropriate5. Raise the nose to the horizon using maximum

allowable G; adjust thrust for level flight6. In steps 3 and 5, avoid stalling the airplane.

Hint for Determining Roll Direction in a Nose High Situation. Unless the airplane is wings level upright or inverted, there will always be a down wing, i.e., a wing that closer to the earth than its opposing wing. This is the wing pointing toward the dark portion of the AI.

To roll to 90o angle of bank, roll so that the down wing moves toward a vertical down position in the dark portion of the AI. Note that the roll is not always in the same direction. If the aircraft is upright, the roll will be in the direction of the down wing, i.e., will be accomplished by pushing the stick toward the down wing and/or or using rudder in the direction of the down wing. If the aircraft is inverted, the roll will be in the direction of the up wing, i.e., will be accomplished by pushing the stick toward the up wing and/or using rudder in the direction of the up wing.

Hint for Determining Roll Direction in a Nose Low Situation. Unless the airplane is wings level upright or inverted, there will always be a down wing, i.e., a wing that closer to the earth than its opposing wing. To roll the shortest direction to wings level upright, push the stick in the direction of the up wing, i.e., roll toward the up wing.


Upset Recovery Techniques for Large Transport Type Airplanes

Boeing. In the 1990s, after several disastrous loss of control accidents provided motivation, the Boeing/Airbus Consortium led the way in developing upset recovery techniques for airliners. The procedures that evolved are summarized in the following table.

Nose High Recovery Nose Low Attitude1. Recognize and confirm the situation2. Disengage autopilot and autothrottle3. Apply as much as full nose-down elevator4. Apply appropriate nose-down stabilizer trim5. Reduce thrust (for underwing-mounted

engines)6. Roll (adjust bank angle) to obtain a nose-

down pitch rate7. Complete the recovery

Roll wings level approaching the horizon Check airspeed and adjust thrust Establish pitch attitude

1. Recognize and confirm the situation2. Disengage autopilot and autothrottle3. Recover from stall, if necessary4. Roll in the shortest direction to wings level

(unload and roll if bank angle is more than 90o)

5. Recover to level flight: Apply nose-up elevator Apply stabilizer trim, if necessary Adjust thrust and drag as necessary

Source: Boeing/Airbus article “Aerodynamic Principles of Large-Airplane Upsets”

The following points are also treated in the Boeing upset recovery paper:

Unusually large amounts of aileron/spoiler input may be required to recover from an upset. Rudder will assist aileron/spoiler input in effecting a roll, especially at low airspeeds. However,

excessive rudder at high AOA/low airspeed may result in departure from controlled flight. If a stall situation exists, stall recovery must occur before upset recovery can commence. If elevator is insufficient to command required pitch changes, then pitch trim (which moves the

entire horizontal tail) can be used. If pitch trim is used to effect nose movement during upset recovery, it will be necessary to readjust

this trim when approaching nose-level upright flight. Adding/reducing thrust in airplanes with engines hung from the wings causes a nose-up/nose-

down pitch, since the thrust is applied below the center of gravity of the airplane. (Note: this statement assumes upright flight; in inverted flight, the pitching moment is nose-down/nose-up.)

Increasing bank angle up to 90o in nose-high recovery turns a pitching moment into a turning moment, allowing the nose to begin falling toward the horizon.

At bank angles greater than 67o, level flight cannot be maintained without exceeding the 2.5G limit which applies to most airliners.

Smooth application of aileron/spoiler should suffice to establish a positive recovery roll rate. If it doesn’t, it may be necessary to apply rudder in the direction of roll. “Too much rudder applied too quickly or held too long may result in loss of lateral and directional control or structural failure.”

At steep nose down pitch angles and high airspeeds (above VMO / MMO), both nose-up elevator and nose-up elevator trim maybe required to establish a nose-up pitch rate.

The paper makes no mention of what may happen to cabin occupants during upset recovery. The procedures for nose low and nose high upset recoveries can be reduced to their common

elements as follows:1. Assess the energy situation (potential, kinetic, energy).2. Understand where the ground is.3. Use whatever authority is required of the flight controls4. Maneuver the airplane to return to normal bank and pitch.


http://faculty.erau.edu/rogersr/as495/manuals/BoeingUpset.htm

Boeing/Doug Forsyth. The paper by Doug Forsyth (Airplane Upset Recovery Training: see bibliography) refines/reorganizes the Boeing recovery strategies given on the previous page. One wonders however whether this refinement is an improvement on the original paper.

Governing generalities are:1. If stalled, first recover from the stall by unloading the airplane and reducing angle of attack.2. The next sequence of techniques depends on events characterizing a particular upset.3. Avoid allowing recovery from one upset cause the aircraft to enter into a second upset.4. Assess energy.5. Always disengage autopilot and autothrottle.6. High bank angle recoveries may involve inverted flight attitude; roll shortest direction to near

wings level upright attitude.

Nose High, Wings Level Recovery Nose Low, Wings Level Recovery1. Apply up to full nose-down elevator to obtain

nose-down pitch rate.2. Consider trimming off control force3. Additional actions if airplane does not

respond: Roll to obtain a nose-down pitch Reduce thrust (underwing mounted

engines)4. If aileron/spoiler control is ineffective, rudder

may be required to induce rolling maneuver Use extreme caution &small rudder input Too much rudder, or rudder applied too

quickly, may result in loss of lateral or directional control

5. Complete the recovery Roll to wings level as nose approaches

the horizon Recover slightly nose low Check airspeed Adjust thrust and pitch as necessary

Low Airspeed1. Airplane may be stalled at low pitch angle2. Return nose to desired pitch3. Avoid Secondary Stall4. Respect G and airspeed limitations

High Airspeed1. Apply nose-up elevator2. Stabilizer trim may be necessary3. Reduce thrust4. Extend speedbrakes as necessary5. Complete the recovery: establish pitch, thrust,

and configuration for required airspeed

High Bank Angle Nose High Recovery High Bank Angle Nose Low Recovery1. Bank angle helps reduce high pitch2. Unload and adjust bank to achieve nose-down

pitch rate3. Complete recovery

Roll wings level as nose approaches horizon

Recover to slightly nose-down attitude Check airspeed Adjust thrust and pitch as necessary

1. Requires prompt action Altitude rapidly exchanged for airspeed Airspeed can increase beyond limits

2. Simultaneous roll and thrust adjustment may be necessary

3. Unloading may be necessary Decrease yoke back pressure; or Push yoke forward to decrease G

4. Use full aileron/spoiler as necessary5. Establish roll rate toward nearest horizon

Do not increase G force or use back yoke until approaching wings level

Use rudder to roll if aileron/spoiler input is ineffective

6. Approaching wings level, complete the recovery: pitch, thrust, configuration for required airspeed.


American. The following recovery techniques are summarized from a video of an American Airlines Upset Training Session conducted for line pilots. PF = pilot flying; PNF = pilot not flying; PFD = primary flight display (AI, A/S, altitude indicator in one glass cockpit instrument). This information has been modified since the crash of American 587 on Long Island in November 2001. American pilots are taught to apply rudder judiciously or not at all in upsets.

Nose High Recovery Nose Low Recovery1. PF disengage autothrottle and autopilot.2. Unload and roll aircraft toward nearest

horizon to lower the nose while maintaining some positive G force.

3. Normally limit bank angle to approximately 70o.

4. Increase thrust in most nose high recoveries.5. As aircraft symbol on PFD approaches the

horizon, make a coordinated rollout to a wings level slightly nose low attitude.

6. Check airspeed and adjust thrust and pitch as necessary.

Other observations: FAA says apply thrust before rolling;

American says roll first, then increase thrust, to respect thrust effect.

Unloading the aircraft ensures rudder and ailerons will remain effective almost to zero airspeed.

Limiting bank angle to 70o makes rollout on horizon easier. At 90o bank, nose low recovery is likely.

Roll first, then apply thrust. Lead the rollout to wings level to wings

level, and maintain5o nose down and 0.5 G until adequate airspeed is obtained.

1. Roll aircraft in shortest direction toward the sky pointer.

2. With bank angles in excess of 90o, maintain neutral to forward yoke pressure.

3. The roll toward the sky pointer should be coordinated (apply rudder in roll direction).

4. With bank angles less than 60o, increase back pressure on yoke.

5. Adjust thrust and utilize drag devices as required. Any speed above or below “corner speed” will result in excessive altitude loss.

Other observations: Goal is to minimize nose drop while

reorienting the lift vector. The sky pointer is the target for the lift

vector. Apply neutral yoke pressure at 90o bank. When inverted, unload and roll first, then

pull. Full forward yoke (elevator use only)

can’t get –1.0 G when inverted. PF should be strapped firmly in seat with

lap belt and shoulder harness. When inverted, unload and roll first, then

pull. The tape does not mention pitch effect of

using thrust to reach cornering speed.

Other important observations on the training tape: To determine bank angle; find sky pointer on PDF. To determine pitch, find horizon lines on PDF if horizon line is not visible. Rudder at high AOA significantly improves roll rate. Don’t overuse rudder in a roll, since over control can result; the application should be slow—

apply rudder over a period of 1-2 seconds. PNF should stay off controls during an upset. Stay in the flight envelope (airspeed and load factor) during recovery from an upset. On a PFD flat panel display, the fixed aircraft symbol is part of the case: “You are strapped to the

fixed aircraft symbol; the screen floats behind you.”


VI. CAUSES OF UPSETS

In a paper presented at a 1997 international aviation conference, Doug Forsythe—at that time Manager of Flight Safety Programs for the Boeing Commercial Airplane Group—categorized the major causes of airplane upsets. These are:

1. Turbulence2. Clear Air Turbulence3. Mountain Wave4. Wake Turbulence (Wingtip Vortices; Jet and Prop Wash)

2. Windshear/Microbursts3. Thunderstorms4. Airplane Icing5. Airplane System Anomalies

Flight Instrument Failures Flight Control Anomalies Autoflight Systems (Auto-Throttle, Auto-Pilot)

6. Human Factors (Pilot Induced) Inattention Distractions Improper Use of Automation

7. Combination of Factors

The first four causes cited by Forsythe are commonly discussed in ERAU courses prerequisite for AS495L, and need not be explained again here. Causes 5 and 6 are self-explanatory, and implicitly stress the importance of pilot situational awareness and professional expertise. Note that Auto-Throttle/Auto-Pilot difficulties listed under Cause 5 lead to the first step in every upset recovery procedure endorsed by a major airline/aircraft manufacturing company: first disengage the auto-throttle and auto-pilot.

A related categorization of the causes of upsets is given in Boeing/Airbus Upset Recovery Manual Part I. (Section 2.4, page 21 of the document). The outline below shows the organization of these categories.

2.4. Causes of Upsets (p. 21 of the document)2.4.1. Environmentally Induced Upsets

2.4.1.1. (Weather) Turbulence2.4.1.1.1. Clear Air Turbulence2.4.1.1.2. Mountain Wave2.4.1.1.3. Windshear2.4.1.1.4. Thunderstorms2.4.1.1.5. Microbursts

2.4.1.2. Wake Turbulence2.4.1.3. Airplane Icing

2.4.2. System-Anomalies-Induced Upsets2.4.2.1. Flight Instruments2.4.2.2. Autoflight Systems2.4.2.3. Flight Controls and Other Anomalies

2.4.3. Pilot-Induced Airplane Upsets2.4.3.1. Instrument Cross Check2.4.3.2. Adjusting Altitude and Power2.4.3.3. Inattention2.4.3.4. Distraction from Primary Cockpit Duties2.4.3.5. Vertigo or Spatial Disorientation2.4.3.6. Pilot Incapacitation2.4.3.7. Improper Use of Automation

2.4.4. Combination of Causes


http://faculty.erau.edu/rogersr/as495/manuals/1stUpset.pdf

The text on upset causes below is copied verbatim from the Boeing/Airbus Manual mentioned above.

2.4 Causes of Airplane UpsetsAirplane upsets are not a common occurrence. This may be for a variety of reasons. Airplane design and certification methods have improved. Equipment has become more reliable. Perhaps training programs have been effective in teaching pilots to avoid situations that lead to airplane upsets. While airplane upsets seldom take place, there are a variety of reasons why they happen. Figure 2 shows incidents and causes from NASA Aviation Safety Reporting System (ASRS) reports. The National Transportation Safety Board analysis of 20 transport-category loss-of-control accidents from 1986 to 1996 indicates that the majority were caused by the airplane stalling (Fig. 3). This section provides a review of the most prevalent causes for airplane upsets.

2.4.1 Environmentally Induced Airplane Upsets

The predominant number of airplane upsets are caused by various environmental factors (Fig. 2). Unfortunately, the aviation industry has the least amount of influence over the environment when compared to human factors or airplane-anomaly-caused upsets. The industry recognizes this dilemma and resorts to training as a means for avoiding environmental hazards. Separate education and training aids have been produced through an industry team process that addresses turbulence, windshear, and wake turbulence.

2.4.1.1 Turbulence (i.e. Weather Caused Turbulence)

Turbulent atmosphere is characterized by a large variation in an air current over a short distance. The main causes of turbulence are jet streams, convective currents, obstructions to wind flow, and windshear. Turbulence is categorized as “light,” “moderate,” “severe,” and “extreme.” Refer to an industry-produced Turbulence Education and Training Aid for more information about turbulence. This aid is available from the National Technical Information Service or The Boeing Company. Only limited information is presented


in this section for a short review of the subject. Knowledge of the various types of turbulence assists in avoiding it and, therefore, the potential for an airplane upset.

In one extreme incident, an airplane encountered severe turbulence that caused the number 2 engine to depart the airplane. The airplane entered a roll 50 deg left, followed by a huge yaw. Several pitch and roll oscillations were reported. The crew recovered and landed the airplane.

2.4.1.1.1 Clear Air Turbulence

Clear air turbulence (CAT) is defined by the Aeronautical Information Manual as “high-level turbulence (normally above 15,000 ft above sea level) not associated with cumuliform cloudiness, including thunderstorms.”

Although CAT can be encountered in any layer of the atmosphere, it is almost always present in the vicinity of jet streams. A number of jet streams (high-altitude paths of winds exceeding velocities of 75 to 100 kn) may exist at any given time, and their locations will vary constantly. CAT becomes particularly difficult to predict as it is extremely dynamic and does not have common dimensions of area or time. In general, areas of turbulence associated with a jet stream are from 100 to 300 mi long, elongated in the direction of the wind; 50 to 100 mi wide; and 2000 to 5000 ft deep. These areas may persist from 30 min


to 1 day. CAT near the jet stream is the result of the difference in wind-speeds and the windshear generated between points. CAT is considered moderate when the vertical windshear is 5 kn per 1000 ft or greater and the horizontal shear is 20 kn per 150 nm, or both. Severe CAT occurs when the vertical shear is 6 kn per 1000 ft and the horizontal shear is 40 kn per 150 nm or greater, or both.

2.4.1.1.2 Mountain WaveMountains are the greatest obstructions to wind flow. This type of turbulence is classified as “mechanical” because it is caused by a mechanical disruption of wind. Over mountains, rotor or lenticular clouds are sure signs of turbulence. However, mechanical turbulence may also be present in air too dry to produce clouds. Light to extreme turbulence is created by mountains. Severe turbulence is defined as that which causes large, abrupt changes in altitude or attitude. It usually causes large variation in indicated airspeed. The airplane may be momentarily out of control.

Severe turbulence can be expected in mountainous areas where wind components exceeding 50 kn are perpendicular to and near the ridge level; in and near developing and mature thunderstorms; occasionally, in other towering cumuliform clouds; within 50 to 100 mi on the cold side of the center of the jet stream; in troughs aloft; and in lows aloft where vertical windshears exceed 10 kn per 1000 ft and horizontal windshears exceed 40 kn per 150 mi. Extreme turbulence is defined as that in which the airplane is violently tossed around and practically impossible to control. It may cause structural damage. Extreme turbulence can be found in mountain-wave situations, in and below the level of well-developed rotor clouds, and in severe thunderstorms.

2.4.1.1.3 Windshear

Wind variations at low altitude have long been recognized as a serious hazard to airplanes during takeoff and approach. These wind variations can result from a large variety of meteorological conditions, such as topographical conditions, temperature inversions, sea breezes, frontal systems, strong surface winds, and the most violent forms of wind change—thunderstorms and rain showers. Thunderstorms and rain showers


may produce an airplane upset, and they will be discussed in the following section. The Windshear Training Aid provides comprehensive information on windshear avoidance and training. This aid is available from the National Technical Information Service or The Boeing Company.

2.4.1.1.4 Thunderstorms

There are two basic types of thunderstorms: airmass and frontal. Airmass thunderstorms appear to be randomly distributed in unstable air, and they develop from localized heating at the Earth’s surface (Fig. 4). The heated air rises and cools to form cumulus clouds. As the cumulus stage continues to develop, precipitation forms in high portions of the cloud and falls. Precipitation signals the beginning of the mature stage and the presence of a downdraft. After approximately an hour, the heated updraft creating the thunderstorm is cut off by rainfall. Heat is removed and the thunderstorm dissipates. Many thunderstorms produce an associated cold-air gust front as a result of the downflow and outrush of rain-cooled air. These gust fronts are usually very turbulent, and they can create a serious airplane upset, especially during takeoff and approach.


Frontal thunderstorms are usually associated with weather systems line fronts, converging wind, and troughs aloft (Fig. 5). Frontal thunderstorms form in squall lines; last several hours; generate heavy rain, and possibly hail; and produce strong gusty winds, and possibly tornadoes. The principal distinction in formation of these more severe thunderstorms is the presence of large, horizontal wind changes (speed and direction) at different altitudes in the thunderstorm. This causes the severe thunderstorm to be vertically tilted. Precipitation falls away from the heated updraft, permitting a much longer storm development period. Resulting airflows within the storm accelerate to much higher vertical velocities, which ultimately results in higher horizontal wind velocities at the surface. The downward moving column of air, or downdraft, of a typical thunderstorm is fairly large, about 1 to 5 mi in diameter. Resultant outflows may produce large changes in windspeed.

2.4.1.1.5 Microbursts

Identification of concentrated, more powerful downdrafts—known as microbursts—has resulted from the investigation of windshear accidents and from meteorological research. Microbursts can occur anywhere convective weather conditions occur. Observations suggest that approximately 5% of all thunderstorms produce a microburst. Downdrafts associated with microbursts are typically only a few hundred to 3000 ft across. When a downdraft reaches the ground, it spreads out horizontally and may form one or more horizontal vortex rings around the downdraft (Fig. 6). Microburst outflows are not always symmetric. Therefore, a significant airspeed increase may not occur upon entering outflows, or it may be much less than the subsequent airspeed loss experienced when exiting the microburst. Windspeeds intensify for about 5 min after a microburst initially contacts the ground and typically dissipate within 10 to 20 min after ground contact. It is vital to recognize that some microbursts cannot be successfully escaped with any known techniques.

2.4.1.2 Wake Turbulence

Wake turbulence is the leading cause of airplane upsets that are induced by the environment. The phenomenon that creates wake turbulence results from the forces that lift the airplane. High-pressure air


from the lower surface of the wings flows around the wingtips to the lower pressure region above the wings. A pair of counter-rotating vortices are thus shed from the wings: the right wing vortex rotates counterclockwise, and the left wing vortex rotates clockwise (Fig. 7). The region of rotating air behind the airplane is where wake turbulence occurs. The strength of the turbulence is determined predominantly by the weight, wingspan, and speed of the airplane. Generally, vortices descend at an initial rate of about 300 to 500 ft/min for about 30 sec. The descent rate decreases and eventually approaches zero at between 500 and 900 ft below the flight path. Flying at or above the flight path provides the best method for avoidance. Maintaining a vertical separation of at least 1000 ft when crossing below the preceding aircraft may be considered safe. This vertical motion is illustrated in Figure 8. Refer to the Wake Turbulence TrainingAid for comprehensive information on how to avoid wake turbulence. This aid is available from the National Technical Information Service or The Boeing Company.

An encounter with wake turbulence usually results in induced rolling or pitch moments; however, in rare instances an encounter could cause structural damage to the airplane. In more than one instance, pilots have described an encounter to be like “hitting a wall.” The dynamic forces of the vortex can exceed the roll or pitch capability of the airplane to overcome these forces. During test programs, the wake was approached from all directions to evaluate the effect of encounter direction on response. One item was common to all encounters: without a concerted effort by the pilot to reenter the wake, the airplane would be expelled from the wake and an airplane upset could occur.

Counter-control is usually effective and induced roll is minimal in cases where the wingspan and ailerons of the encountering airplane extend beyond the rotational flowfield of the vortex (Fig. 9). It is more difficult for airplanes with short wingspan (relative to the generating airplane) to counter the imposed roll induced by the vortex flow.


Avoiding wake turbulence is the key to avoiding many airplane upsets. Pilot and air traffic control procedures and standards are designed to accomplish this goal, but as the aviation industry expands, the probability of an encounter also increases.

2.4.1.3 Airplane Icing

Technical literature is rich with data showing the adverse aerodynamic effects of airfoil contamination. Large degradation of airplane performance can result from the surface roughness of an extremely small amount of contamination. These detrimental effects vary with the location and roughness, and they produce unexpected airplane handling characteristics, including degradation of maximum lift capability, increased drag, and possibly unanticipated changes in stability and control. Therefore, the axiom of “Keep it clean” for critical airplane surfaces continues to be a universal requirement.

2.4.2 Systems-Anomalies-Induced Airplane Upsets

Airplane designs, equipment reliability, and flight crew training have all improved since the Wright brothers’ first powered flight. Airplane certification processes and oversight are rigorous. Airline and manufacturers closely monitor equipment failure rates for possible redesign of airplane parts or modification of maintenance procedures. Dissemination of information is rapid if problems are detected. Improvement in airplane designs and equipment components has always been a major focus in the aviation industry. In spite of this continuing effort, there are still failures. Some of these failures can lead to an airplane upset. That is why flight crews are trained to overcome or mitigate the impact of the failures. Most failures are survivable if correct responses are made by the flight crew.

An airplane was approaching an airfield and appeared to break off to the right for a left downwind to the opposite runway. On downwind at approximately 1500 ft, the airplane pitched up to nearly 60 deg and climbed to an altitude of nearly 4500 ft, with the airspeed deteriorating to almost 0 kn. The airplane then tail-slid, pitched down, and seemingly recovered. However, it continued into another steep pitchup of 70 deg. This time as it pitched down and descended again, seemingly recovering, the airplane impacted the ground in a flat pitch, slightly right wing down. The digital flight data recorder indicated that the stabilizer trim was more than 13 units nose up. The flight crew had discussed a trim problem during the descent but


made no move to cut out the electric trim or to manually trim. The accident was survivable if the pilot had responded properly.

2.4.2.1 Flight Instruments

The importance of reliable flight instruments has been known from the time that pilots first began to rely on artificial horizons. This resulted in continual improvements in reliability, design, redundancy, and information provided to the pilots.

However, instrument failures do infrequently occur. All airplane operations manuals provide flight instrument system information so that when failures do happen, the pilot can analyze the impact and select the correct procedural alternatives. Airplanes are designed to make sure pilots have at least the minimum information needed to safely control the airplane.

In spite of this, several accidents point out that pilots are not always prepared to correctly analyze the alternatives, and an upset takes place. During the takeoff roll, a check of the airspeed at 80 kn revealed that the Captain’s airspeed was not functioning. The takeoff was continued. When the airplane reached 4700 ft, about 2 min into the flight, some advisory messages appeared informing the crew of flight control irregularities. Comments followed between the pilots about confusion that was occurring between the airspeed indication systems from the leftside airspeed indication system, affecting the indication of the leftside airspeed autopilot and activation of the overspeed warning. The airplane continued flying with the autopilot connected and receiving an erroneous indication in the Captain’s airspeed. Recorded sounds and flight data indicated extreme conditions of flight, one corresponding to overspeed and the other to slow speed (stick shaker). The Captain initiated an action to correct the overspeed, and the copilot advised that his airspeed indicator was decreasing. The airplane had three airspeed indicating systems, and at no time did the flight crew mention a comparison among the three systems. The flight recorders indicated the airplane was out of control for almost 2 min until impact. Experts determined that the anomalies corresponded to conditions equal to an obstruction in the Captain’s airspeed sensors (pitot head).

2.4.2.2 Autoflight Systems

Autoflight systems include the autopilot, autothrottles, and all related systems that perform flight management and guidance. The systems integrate information from a variety of other airplane systems. They keep track of altitude, heading, airspeed, and flight path with unflagging accuracy. The pilot community has tended to develop a great deal of confidence in the systems, and that has led to complacency in some cases. As reliable as the autoflight systems may be, they can, and have, malfunctioned. Because of the integration of systems, it may even be difficult for the pilot to analyze the cause of the anomaly, and airplane upsets have occurred. Since advanced automation may tend to mask the cause of the anomaly, an important action in taking control of the airplane is to reduce the level of automation. Disengaging the autopilot, the autothrottles, or both, may help in analyzing the cause of the anomaly by putting the pilot in closer touch with the airplane and perhaps the anomaly.

2.4.2.3 Flight Control and Other Anomalies

Flight control anomalies, such as flap asymmetry, spoiler problems, and others, are addressed in airplane operations manuals. While they are rare events, airplane certification requirements ensure that pilots have sufficient information and are trained to handle these events. However, pilots should be prepared for the unexpected, especially during takeoffs. Engine failure at low altitudes while the airplane is at a low-energy condition is still a demanding maneuver for the pilot to handle. An erroneous stall warning on takeoff or shortly after takeoff could be a situation that allows the airplane to become upset.

2.4.3 Pilot-Induced Airplane Upsets

We have known for many years that sensory inputs can be misleading to pilots, especially when they cannot see the horizon. To solve this problem, airplanes are equipped with flight instruments to provide the necessary information for controlling the airplane.


2.4.3.1 Instrument Cross-Check

Pilots must crosscheck and interpret the instruments and apply the proper pitch, bank, and power adjustments. Misinterpretation of the instruments or slow crosschecks by the pilot can lead to an airplane upset.

An important factor influencing crosscheck technique is the ability of the pilot: “All pilots do not interpret instrument presentations with the same speed; some are faster than others in understanding and evaluating what they see. One reason for this is that the natural ability of pilots varies. Another reason is that the experience levels are different. Pilots who are experienced and fly regularly will probably interpret their instruments more quickly than inexperienced pilots.” [Source: Instrument Flight Procedures. Air Force Manual 11217, Vol. 1 (1 April 1996).]

2.4.3.2 Adjusting Attitude and Power

A satisfactory instrument crosscheck is only one part of the equation. It is necessary for the pilot to make the correct adjustments to pitch, bank, and power in order to control the airplane. Airplane upsets have occurred when the pilot has made incorrect adjustments. This can happen when the pilot is not familiar with the airplane responses to power adjustments or control inputs. There have also been instances when two pilots have applied opposing inputs simultaneously.

2.4.3.3 Inattention

A review of airplane upsets shows that inattention or neglecting to monitor the airplane performance can result in minor excursions from normal flight regimes to extreme deviations from the norm. Many of the minor upsets can be traced to an improper instrument crosscheck; for example, neglecting to monitor all the instruments or fixating on certain instrument indications and not detecting changes in others. Some instrument indications are not as noticeable as others. For example, a slight heading change is not as eye-catching as a 1000ft/min change in vertical velocity indication.

There are many extreme cases of inattention by the flight crew that have resulted in airplane upset accidents. In one accident, a crew had discussed a recurring autothrottle problem but continued to use the autothrottle. On leveloff from a descent, one throttle remained at idle and the other compensated by going to a high power setting. The resulting asymmetric thrust exceeded the autopilot authority and the airplane began to roll. At approximately 50 deg of bank, full pro-roll lateral control wheel was applied. The airplane rolled 168 deg into a steep dive of 78 deg, nose low, and crashed.

2.4.3.4 Distraction From Primary Cockpit Duties

“Control the airplane first” has always been a guiding principle in flying. Unfortunately, it is not always followed. In this incident, both pilots were fully qualified as pilot-in-command and were supervising personnel. The Captain left the left seat, and the copilot set the airplane on autopilot and went to work on a clipboard on his lap. At this point the autopilot disengaged, possibly with no annunciator light warning. The airplane entered a steep, nose-down, right spiral. The copilot’s instrument panel went blank, and he attempted to use the pilot’s artificial horizon. However, it had tumbled. In the meantime, the Captain returned to his station and recovered the airplane at 6000 ft using needle and ball. This is just one of many incidents where pilots have become distracted. Many times, the distraction is caused by relatively minor reasons, such as caution lights or engine performance anomalies.

2.4.3.5 Vertigo or Spatial Disorientation

Spatial disorientation has been a significant factor in many airplane upset accidents. The definition of spatial disorientation is the inability to correctly orient oneself with respect to the Earth’s surface. A flight crew was climbing to about 2000 ft at night during a missed approach from a second Instrument Landing System (ILS) approach. The weather was instrument meteorological conditions (IMC)– ceiling: 400 ft,


visibility: 2 mi, rain, and fog. The airplane entered a spiral to the left. The Captain turned the controls over to the First Officer, who was unsuccessful in the recovery attempt. The airplane hit trees and was destroyed by ground impact and fire. [NTSB/AAR9205]

All pilots are susceptible to sensory illusions while flying at night or in certain weather conditions. These illusions can lead to a conflict between actual attitude indications and what the pilot “feels” is the correct attitude. Disoriented pilots may not always be aware of their orientation error. Many airplane upsets occur while the pilot is busily engaged in some task that takes attention away from the flight instruments. Others perceive a conflict between bodily senses and the flight instruments but allow the airplane to become upset because they cannot resolve the conflict. Unrecognized spatial disorientation tends to occur during task-intensive portions of the flight, while recognized spatial disorientation occurs during attitude-changing maneuvers.

There are several situations that may lead to visual illusions and then airplane upsets. A pilot can experience false vertical and horizontal cues. Flying over sloping cloud decks or land that slopes gradually upward into mountainous terrain often compels pilots to fly with their wings parallel to the slope, rather than straight and level. A related phenomenon is the disorientation caused by the Aurora Borealis in which false vertical and horizontal cues generated by the aurora result in attitude confusion.

It is beyond the scope of this training aid to expand on the physiological causes of spatial disorientation, other than to alert pilots that it can result in loss of control of an airplane. It should be emphasized that the key to success in instrument flying is an efficient instrument crosscheck. The only reliable aircraft attitude information, at night or in IMC, is provided by the flight instruments. Any situation or factor that interferes with this flow of information, directly or indirectly, increases the potential for disorientation. The pilot’s role in preventing airplane upsets due to spatial disorientation essentially involves three things: training, good flight planning, and knowledge of procedures. Both pilots must be aware that it can happen, and they must be prepared to control the airplane if the other person is disoriented.

2.4.3.6 Pilot IncapacitationA First Officer fainted while at the controls enroute to the Azores, Portugal. He slumped against the controls, and while the rest of the flight crew was removing him from his flight position, the airplane pitched up and rolled to over 80 deg of bank. The airplane was then recovered by the Captain. While this is a very rare occurrence, it does happen, and pilots need to be prepared to react properly. Another rare possibility for airplane upset is an attempted hijack situation. Pilots may have very little control in this critical situation, but they must be prepared to recover the airplane if it enters into an upset.

2.4.3.7 Improper Use of Airplane Automation

The following incident describes a classic case of improper use of airplane automation. “During an approach with autopilot 1 in command mode, a missed approach was initiated at 1500 ft. It is undetermined whether this was initiated by the pilots; however, the pilot attempted to counteract the autopilot-commanded pitchup by pushing forward on the control column. Normally, pushing on the control column would disengage the autopilot, but automatic disconnect was inhibited in go-around mode in this model airplane. As a result of the control column inputs, the autopilot trimmed the stabilizer to 12 deg, nose up, in order to maintain the programmed go-around profile. Meanwhile, the pilot-applied control column forces caused the elevator to deflect 14 deg, nose down. The inappropriate pilot-applied control column forces resulted in three extreme pitchup stalls before control could be regained. The airplane systems operated in accordance with design specifications.” [FSF, Flight Safety Digest 1/92]

The advancement of technology in today’s modern airplanes has brought us flight directors, autopilots, autothrottles, and flight management systems. All of these devices are designed to reduce the flight crew workload. When used properly, this technology has made significant contributions to flight safety. But technology can include complexity and lead to trust and eventual complacency. The systems can sometimes do things that the flight crew did not intend for them to do. Industry experts and regulators continue to work together to find the optimal blend of hardware, software, and pilot training to ensure the highest possible level of system performance—which centers on the human element.


2.4.4 Combination of Causes

A single cause of an airplane upset can be the initiator of other causes. In one instance, a possible inadvertent movement of the flap/slat handle resulted in the extension of the leading edge slats. The Captain’s initial reaction to counter the pitchup was to exert forward control column force; the control force when the autopilot disconnected resulted in an abrupt airplane nose-down elevator command. Subsequent commanded elevator movements to correct the pitch attitude induced several violent pitch oscillations. The Captain’s commanded elevator movements were greater than necessary because of the airplane’s light control force characteristics. The oscillations resulted in a loss of 5000 ft of altitude. The maximum nose-down pitch attitude was greater than 20 deg, and the maximum normal accelerations were greater than 2 g and less than 1 g. This incident lends credence to the principle used throughout this training aid: Reduce the level of automation while initiating recovery; that is, disconnect the autopilot and autothrottle, and do not let the recovery from one upset lead to another.


VII. LOSS OF CONTROL ACCIDENT / INCIDENT ANALYSES

Accident/Incident Summaries

ACCIDENT/INCIDENT PRIMARY IDEAS / POINTS OF INTERESTUSAir 427 B737-300 Aliquippa, PA

8 September 1994Rudder Hard Over; Rudder Reversal; Accelerated Stall; Terrain Impact; Possibly Recoverable; Course Web Site Video

UAL 585 B737-200 Colorado Springs, CO3 March 1991

Rudder Hard Over; Rudder Reversal; Terrain Impact; Probably Not Recoverable; Course Web Site Video

Eastwind 517 B737-200 Richmond, VA10 June 1996

Rudder Excursions; Uncalled Roll and Pitch; Recovered; Course Web Site Video

China Air MD11 Shemya, AK6 April 1993

High Altitude Inadvertant Slat Deployment; 5000’ Altitude Loss; Pitch Oscillations; Insufficient Upset Training; Disuse of Seat Restraints; Recovered: 2 Fatal, 60 Serious, 96 Minor

AA A300 West Palm Beach, FL12 May 1997

Inadvertent Stall; Uncalled Roll; Pilot Error; Improper Use of Autothrottle. Recovered: 1 Serious, 1 Minor

Continental DC-10 Los Angeles, CA23 May 1998

Nose Up Pitch and High G; Autopilot Malfunction; Repeat Maintenance Gripes; Recovered: 4 Serious, 5 Minor

American West B757 Agua Caliente, AZ20 September 1999

GPWS Activation Due to A/C at Lower Altitude; Sudden Escape Pull-up; Recovered: 2 Serious; 2 Minor

AA 587 A300-600 Long Island, NY12 November 2001

Rudder Cycling; Yaw Oscillations; Inflight Structural Failure; Wingtip Vortices; Course Notes (p. 31) and Web Site Manuals: NTSB, Boeing, and Airbus Documents; Terrain Impact

AA 191 Chicago O’Hare, IL29 May 1979

Engine Fell Off Plane on T/O; Faulty Maintenance Procedures; Effect of Structural Damage on VMCA

TWA B727 Saginaw, MI4 April 1979

Asymmetrical Slat Deployment; Uncontrolled roll and pitch; Actuator Malfunction; 30,000’+ Altitude Loss; Improper use of Flight Controls; Landing Gear Extension; Recovered

Delta 106 B767-332 JFK, NY30 March 2000

Pilot Disorientation; Rudder to Assist Roll; Delta (Critical Aircraft Situational Training); Recovered; Web Site Manuals

Sky Train Learjet 24 Felt, OK1 October 1981

Airspeed Overspeed; Deficient Aircrew Training; Vmo, Mmmo; High Speed vs. Low Speed Stall; Mach Tuck; Marginal A/C Controllability; Need to Lower Landing Gear; Terrain Impact

China Airlines 006 B747-SP Pacific Ocean19 February 1985

Asymmetrical Thrust; Pilot Inattention/Disorientation; Over-reliance on Autopilot; Uncontrolled Roll/Pitch with Descent from FL410 to 9,500’ MSL; recovered: 2 Serious

United 232 DC-10-10 Sioux City, IA19 July 1989

Hydraulically Actuated Flight Control Failure; Differential Thrust to Control Pitch and Yaw; Phugoid Pitch Oscillations; Terrain Impact: 111 Fatal, 47 Serious, 125 Minor, 13 None


http://faculty.erau.edu/rogersr/as495/manuals/manuals.html


http://faculty.erau.edu/rogersr/as495/videos/allAttitudeVideos.html



US Air Flight 427 B737-300 Accident at Aliquippa, Pennsylvania on September 8, 1994

Documentation. NTSB AAR-99/01 “Uncontrolled Descent and Collision with Terrain.” Web file:http://www.ntsb.gov/publictn/1999/AAR9901.pdf

Summary. The aircraft experienced a hard-over rudder situation at low altitude while maneuvering to land. It subsequently entered uncontrolled flight characterized by rapid roll in the direction of yaw caused by rudder displacement. A steep nose down attitude and ground impact resulted.

Analysis. Flight recorder tapes reveal that both pilots held the yoke full back (resulting in full up elevator) for the twenty seconds of the flight immediately before terrain impact. The resultant accelerated stall and associated high induced drag ensured that the plane could not accelerate to “flying” speed and hence recover from its steep nose down attitude. It has been conjectured that there might have been some hope of raising the nose if yoke back pressure had been released initially, allowing the airspeed to increase and providing adequate airspeed to allow subsequent up elevator to raise the nose of the aircraft to the horizon prior before terrain impact.

The following is pasted verbatim from the NTSB Web Site

Synopsis: On September 8, 1994, about 1903:23 eastern daylight time, USAir (now US Airways) flight 427, a Boeing 737-3B7 (737-300), N513AU, crashed while maneuvering to land at Pittsburgh International Airport, Pittsburgh, Pennsylvania. Flight 427 was operating under the provisions of 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight from Chicago-O'Hare International Airport, Chicago, Illinois, to Pittsburgh. The flight departed about 1810, with 2 pilots, 3 flight attendants, and 127 passengers on board. The airplane entered an uncontrolled descent and impacted terrain near Aliquippa, Pennsylvania, about 6 miles northwest of the destination airport. All 132 people on board were killed, and the airplane was destroyed by impact forces and fire. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.

The National Transportation Safety Board determines that the probable cause of the USAir flight 427 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide.

The safety issues in this report focused on Boeing 737 rudder malfunctions, including rudder reversals; the adequacy of the 737 rudder system design; unusual attitude training for air carrier pilots; and flight data recorder (FDR) parameters.

Safety recommendations concerning these issues were addressed to the Federal Aviation Administration (FAA). Also, as a result of this accident, the Safety Board issued a total of 22 safety recommendations to the FAA on October 18, 1996, and February 20, 1997, regarding operation of the 737 rudder system and unusual attitude recovery procedures. In addition, as a result of this accident and the United Airlines flight 585 accident (involving a 737-291) on March 3, 1991, the Safety Board issued three recommendations (one of which was designated “urgent”) to the FAA on February 22, 1995, regarding the need to increase the number of FDR parameters.


http://www.ntsb.gov/publictn/1999/AAR9901.pdf

United Flight 585 B737-200 at Colorado Springs, Colorado on March 3, 1991

Documentation. NTSB AAR-01/01 “Uncontrolled Descent and Collision with Terrain.”Web File: http://www.ntsb.gov/publictn/2001/AAR0101.pdf

Summary. On final approach in VMC, the B737-200 aircraft rolled to the right together with a nose down pitch that reached near the vertical before terrain impact. The probably cause of the accident was rudder deflection to the blowdown limit opposite to the rudder direction commanded by the pilot. This was caused by a failure/jam of the rudder power-control unit. Inconclusive evidence exists as to whether weather related phenomena—rotors, mountain waves, &c—contributed to the accident.

Analysis. Full left aileron input during right rudder reversal might have allowed the crew to maintain control had it been applied immediately.

Conclusion. The NTSB carefully studied a subsequent B727 uncontrolled ground impact in 1994 due to uncommanded rudder deflection. Subsequently the AAR for United Flight 585 was rewritten to reflect the information stated conclusions reflected above. (The original AAR for Flight 585 did not attribute the crash to uncommanded rudder deflection.) Subsequently pilot techniques were developed to counter B727 full rudder deflection successfully (assuming the control inputs are applied promptly and correctly). These techniques are not a common part of B737-200 airline training. However, the NTSB also concluded that the crew of United Flight 585 could not reasonably have been expected to analyze and react appropriately to their low altitude emergency given the time available to them before ground impact. First, the Flight 585 crew had not been trained in procedures to counter full 737 rudder deflection. Second, they had not even been alerted to the possibility that such a control anomaly could occur.

Note. The two accidents discussed above—among others--were extremely influential in motivating airline companies—especially U.S. airline companies—to emphasize upset training for line pilots.

The following two paragraphs are pasted verbatim from the NTSB Web Site

Synopsis: On March 3, 1991, a United Airlines Boeing 737, registration number N999UA, operating as flight 585, was on a scheduled passenger flight from Denver, Colorado, to Colorado Springs, Colorado. Visual meteorological conditions prevailed at the time, and the flight was on an instrument flight rules flight plan. Numerous witnesses reported that shortly after completing its turn onto the final approach course to runway 35 at Colorado Springs Municipal Airport, about 0944 mountain standard time, the airplane rolled steadily to the right and pitched nose down until it reached a nearly vertical attitude before hitting the ground in an area known as Widefield Park. The airplane was destroyed, and the 2 flight crewmembers, 3 flight attendants, and 20 passengers aboard were fatally injured.

The National Transportation Safety Board determines that the probable cause of the United Airlines flight 585 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide.


http://www.ntsb.gov/publictn/2001/AAR0101.pdf

Eastwind Flight 517 Incident(pasted verbatim from the NTSB web site)

DCA96IA061

On June 10, 1996, Eastwind Airlines flight 517, a Boeing 737-201, N221US, experienced a reported loss of rudder control while on approach to Richmond, Virginia. The airplane was on a regularly scheduled passenger flight from Trenton, NJ to Richmond. There were 48 passengers, 2 pilots and 3 flight attendants on board. There were no injuries or damage to the airplane as a result of the incident. At the time of the event the airplane's airspeed was about 250 knots and at 4,000 feet MSL.

The captain reported that he was hand flying the airplane and he felt a slight rudder "bump" to the right. He asked the first officer if he had felt the bump, then the airplane suddenly rolled to the right. He reported that he applied opposite rudder but that the rudder felt stiff. He stated the he applied opposite aileron and used asymmetric power to keep the airplane upright. He stated that after he declared an emergency to the approach controller, he and the first officer performed the emergency checklist. The captain reported that as part of the checklist they turned off the yaw damper. He reported that the airplane became controllable, but was not certain if the problem when away at the same time that the yaw damper was turned off.

It is reported that the airplane has previously had problems with uncommanded rudder deflections. Previous reports have been of "rudder bumps" during departure and that the airplane would not trim properly. The FDR was removed from the airplane for examination.


China Eastern Airlines MD-11 at Shemya, AK on April 6, 1993(pasted verbatim from NTSB web site—obvious typos corrected)

SEE NTSB BLUE COVER FACTUAL ACCIDENT REPORT - NTSB/AAR- 93/07

NTSB Identification: DCA93MA037 . The docket is stored on NTSB microfiche number 48295.

Scheduled 14 CFRPart 129 operation of Foreign CHINA EASTERN AIRLINES Accident occurred Tuesday, April 06, 1993 at SHEMYA, AK Aircraft:MCDONNELL DOUGLAS MD-11, registration: B2171 Injuries: 2 Fatal, 60 Serious, 96 Minor, 97 Uninjured.

FLIGHT 583 WAS LEVEL AT 33,000 FEET WHEN THE LEADING EDGE SLATS DEPLOYED INADVERTENTLY. THE AUTOPILOT DISCONNECTED AND THE CAPTAIN WAS MANUALLY CONTROLLING THE AIRPLANE WHEN IT PROGRESSED THROUGH SEVERAL VIOLENT PITCH OSCILLATIONS AND LOST 5,000 FEET. THE SAFETY BOARD DETERMINED THAT THE INADVERTENT DEPLOYMENT OF THE SLATS WAS THE RESULT OF AN INADEQUATELY DESIGNED FLAP/SLAT HANDLE THAT ALLOWED THE HANDLED TO BE EASILY AND INADVERTENLY DISLODGED FROM THE UP/RET POSITION, THEREBY CAUSING SLAT EXTENSION.

The National Transportation Safety Board determines the probable cause(s) of this accident/incident as follows.

THE NATIONAL TRANSPORTATION SAFETY BOARD DETERMINES THAT THE PROBABLE CAUSE OF THIS ACCIDENT WAS THE INADEQUATE DESIGN OF THE FLAP/SLAT ACTUATION HANDLE BY THE DOUGLAS AIRCRAFT COMPANY THAT ALLOWED THE HANDLE TO BE EASILY AND INADVERTENTLY DISLODGED FROM THE UP/RET POSITION, THEREBY CAUSING EXTENSION OF THE LEADING EDGE SLATS DURING CRUISE FLIGHT. THE CAPTAIN'S ATTEMPT TO RECOVER FROM THE SLAT EXTENSION, GIVEN THE REDUCED LONGITUDINAL STABILITY AND THE ASSOCIATED LIGHT CONTROL FORCE CHARACTERISTICS OF THE MD-11 IN CRUISE FLIGHT, LED TO SEVERAL VIOLENT PITCH OSCILLATIONS. CONTRIBUTING TO THE VIOLENCE OF THE PITCH OSCILLATIONS WAS THE LACK OF SPECIFIC MD-11 PILOT TRAINING IN RECOVERY FROM HIGH ALTITUDE UPSETS, AND THE INFLUENCE OF THE STALL WARNING SYSTEM ON THE CAPTAIN'S CONTROL RESPONSES. CONTRIBUTING TO THE SEVERITY OF THE INJURIES WAS THE LACK OF SEAT RESTRAINT USAGE BY THE OCCUPANTS.


American Airlines A300 at West Palm Beach, FL on May 12, 1997(Pasted verbatim from NTSB web site)

NTSB Identification: DCA97MA049 . The docket is stored in the (offline) NTSB Imaging System.

Scheduled 14 CFR Part 121 operation of Air Carrier AMERICAN AIRLINES Accident occurred Monday, May 12, 1997 at WEST PALM BEACH, FL Aircraft:Airbus Industrie A300B4-605R, registration: N90070 Injuries: 1 Serious, 1 Minor, 163 Uninjured.

The flight was assigned an airspeed of 230 knots and cleared to descend from FL240 to 16,000 feet in preparation for landing at Miami. The FDR indicated that while the autopilot was engaged in the descent, the power levers moved from the mechanical autothrottle limit of 44 degrees to the manual limit of 37 degrees. As the aircraft leveled at 16,000 feet the airspeed decreased. The F/O began a right turn to enter a holding pattern and added some power, which stabilized the airspeed at 178 knots. However, the right bank and the resultant angle of attack (AOA) continued to increase, despite left aileron input by the autopilot. As the autopilot reached the maximum input of 20 degrees, bank angle increased past 50 degrees, and the AOA increased rapidly from 7 degrees to 12 degrees. At this point the stick shaker activated, the autopilot independently disconnected, the power was increased, and full left rudder was used to arrest the roll. The bank angle reached 56 degrees, and the AOA reached 13.7 degrees at 177 knots. The aircraft then pitched down, and entered a series of pitch, yaw, and roll maneuvers as the flight controls went through a period of oscillations for about 34 seconds. The maneuvers finally dampened and the crew recovered at approximately 13,000 feet. One passenger was seriously injured and one flight attendant received minor injuries during the upset. According to wind tunnel and flight test data the A300 engineering simulator should adequately represent the aircraft up to 9 degrees AOA. Unlike the accident aircraft; however, the simulator recovered to wings level promptly when the lateral control inputs recorded by the FDR were used. The roll disagreement between the simulator and accident aircraft began at 7 degrees AOA, and it appears that some effect not modeled in the simulator produced the roll discrepancy. Just prior to the upset the accident aircraft entered a cloud deck. The winds were approximately 240 degrees, 35 knots, and the ambient air temperature was approximately minus 4 degrees C. An atmospheric disturbance or asymmetric ice contamination were two possible explanations considered, but unproven.


The flightcrew's failure to maintain adequate airspeed during level off which led to an inadvertent stall, and their subsequent failure to use proper stall recovery techniques. A factor contributing to the accident was the flightcrew's failure to properly use the autothrottle.


Continental Airlines DC-10 at Los Angeles California on May 21, 1998(Pasted verbatim from NTSB web site)

NTSB Identification: LAX98FA169 . The docket is stored in the (offline) NTSB Imaging System.

Scheduled 14 CFRPart 121 operation of Air Carrier CONTINENTAL AIRLINES Accident occurred Thursday, May 21, 1998 at LOS ANGELES, CA Aircraft:McDonnell Douglas DC-10-10, registration: N68043 Injuries: 4 Serious, 5 Minor, 289 Uninjured.

The aircraft was climbing in smooth air about 500 feet per minute with the No. 1 autopilot engaged. The captain reported that the aircraft began a sudden and hard uncommanded 2g pull-up, with the control yoke moving rapidly aft. He immediately grabbed the control yoke, disengaged the autopilot, and leveled the aircraft. Three flight attendants in the aft galley and one passenger in an aft lavatory sustained serious injuries. The aft galley flight attendants described the onset of the event as 'being pulled to the floor by what felt like a strong pull of gravity.' The force suddenly reversed and the three were 'thrown up into the ceiling.' Another force reversal followed and the three were 'slammed down against the floor.' The flight attendants said that a 'roller coaster' type movement then occurred, which quickly damped into a steady state. Review of the aircraft's maintenance records for the year preceding the accident revealed over 50 discrepancies for autopilot system uncommanded disconnects, uncommanded pitch-ups, and failures to engage. Review of the DFDR data revealed that as the aircraft passed through 29,200 feet, four pitch cycles were recorded over a 15-second time period and were accompanied by vertical accelerations, the most severe of which was between 1.84 and -0.12 g's. The initial uncommanded nose pitch-up was preceded by an autopilot controlled movement of the left inboard elevator. The subsequent elevator movements and resultant pitch excursions were due to the pilot's control inputs. With the exception of the captain's and first officer's control wheel sensor units, all autopilot systems passed functional checks. Postaccident test of the first officer's control wheel sensor unit showed an out of tolerance and drifting null signal for the strain gage which provides pitch signal input to the No. 1 autopilot. After about 3 minutes, the signal became noisy and jumped to values of up to 4 volts several times. Many spikes were also observed at values under 3.5 volts (signals over 3.5 volts trigger an automatic disengagement of the autopilot). Subsequent examination of the pitch strain gages by optical magnification found a foreign black-gray metallic-like substance bridging the terminal lug ends. Analysis showed the material was a silver based conductive substance, lying below a factory applied sealing layer, which was introduced during manufacture. The solder on the lugs and the wire used between the lugs and terminals was found not to be consistent with the manufacturer's specifications.


The contaminated strain gage, which resulted in shorting of the strain gage's terminal lugs which lead to excessive autopilot initiated elevator movement, and excessive elevator actuation during recovery by the captain. Contributing factors were the failure of the airline maintenance department to diagnose and correct a historical problem with the autopilot system and the manufacturer's inadequate quality assurance program.


American West B757 at Agua Caliente, AZ on September 20, 1999

(Pasted verbatim from NTSB web site)

NTSB Identification: LAX99FA315. The docket is stored on NTSB microfiche number DMS.

Scheduled 14 CFRPart 121 operation of Air Carrier AMERICA WEST AIRLINES, INC. Accident occurred Monday, September 20, 1999 at AGUA CALIENTE, AZ Aircraft: Boeing 757-2S7, registration: N904AW Injuries: 2 Serious, 2 Minor, 173 Uninjured.

During a Ground Proximity Warning System (GPWS) warning escape maneuver at 27,100 feet, 4 flight attendants (FA's) were injured, 2 of them seriously with fractured leg bones. The injured FA's were standing in the aft galley securing from the meal service when the event occurred and the passengers were seated with belts fastened. In response to an ATC instruction, the flight was descending to maintain 27,000 feet; the controller had told the crew to maintain a good rate of descent (the airplane was descending about 4,000 feet per minute), and an indicated airspeed of 300 knots or greater. The flight was in instrument meteorological conditions at the time and had no outside visual reference. The controller advised the flight of opposite direction traffic at 26,000 feet and a traffic alert symbol was being displayed on the crew's TCAS indicator. As the flight was leveling off at 27,000, the opposite direction traffic passed almost directly beneath the flight. Immediately, the GPWS annunciated the warning, "terrain, whoop, whoop, pull-up." In accordance with the mandatory provisions of the company flight operations manual, the crew executed the proscribed escape maneuver, which, in part, calls for an aggressive application of thrust and a rapid nose pitch up to a 20-degree attitude. Later analysis of the DFDR data showed that the crew only rotated the nose to an 8-degree nose up attitude during the maneuver. During the maneuver, the g-loads generated on the airplane varied between +2.5 and +0.5 over a 2-second time period, which was caused the FA's injuries. As part of the investigation, this flight's profile was flown in a Boeing 757 simulator four times. When flown according to operations manual instructions, the g-loads generated ranged from a low of+2.0 to a high of +4.0. It should be noted that the simulator computer computes the g-loads and can display them to the instructor; however, the simulator does not generate visceral feedback to the crew of the amount of g's being experienced. As early as 1988, Boeing became aware that the dash number model GPWS computer installed in the airplane was subject to issuing false warnings when the airplane overflew another airplane. In response, Boeing issued an all operators letter advising of the problem and issued a service letter in 1989 advising of an upgrade to the GPWS computer to prevent false nuisance warnings. Between 1987 and 1999, 3 service bulletins and 13 service letters were issued advising of modifications to the GPWS and Radio Altitude systems to prevent false warnings. None of these improvements were accomplished by the airline, and the GPWS unit installed in the accident airplane was three upgrades behind the current configuration. The company decision to do Service Bulletin upgrades was based applicability, priority, and budget availability. Service Letters were not routinely reviewed when received, but were filed for later review when discrepancy history patterns indicated a need. For the Boeing 757, the GPWS, TCAS, and Radio Altitude (RA) systems are all interrelated, with the captain's (left side) RA unit providing data input to the GPWS and the TCAS. Review of the maintenance records disclosed that in the 16 months prior to the accident, the GPWS and/or RA systems on this airplane were written up as erratic, providing false warnings, or inoperable 45 times, with 18 discrepancies written up in the 60 days prior to the accident. On three occasions, the GPWS system provided terrain warnings at high altitudes when flying a profile very similar to the accident flight. In accordance with the maintenance manual procedures, the corrective actions largely consisted of removal and replacement of the affected units or sub units. No evidence was found of any diagnostic trouble shooting procedures outside of those specified in the maintenance manuals undertaken by the airline. The airline's maintenance operations control has a system to track problematic airplanes for special maintenance attention, which requires three write-ups in the same ATA code within 10 days to trigger an alert; the accident airplane's discrepancy history pattern fell outside of this "3 in 10" trigger parameter. Flight crews have no ready access to this system and only see on a routine basis the last 10 log sheets where discrepancies are entered. In the 60 days systems was conducted three times in response to continued problems with these systems, with no conclusive hard faults identified. At the end of this 60-day period the RA units were being examined at the system's manufacturer due to a failure that could not be replicated in testing, the manufacturer told the airline that it was aware that the


system's central processors could become desynchronized during power transfers and cause erratic behavior in the units. Another cause of earlier (problem corrected before accident flight) erratic behavior in the airplane's RA system was the installation by maintenance of antennas that were incompatible with the computer units; this was due to the airline parts stocking system that carried all dash number models under the same part number.


the systemic failure of the airline's maintenance department to identify and correct the long standing history of intermittent faults, nuisance warnings, and erratic behavior in this airplane's GPWS system. Also causal is the airline's failure to perform the service bulletins and service letter upgrades to the system, which would have eliminated or greatly reduced the likelihood of this particular nuisance warning, a condition that was identified and corrected by the manufacturers 11 years prior to the accident, and was the subject of one or more of the SB/SL upgrades.


American Flight 587 at Rockaway, N.Y., November 12, 2001

Airbus A300-600 lost rudder, vertical fin, and one engine apparently as a result of attempts to recover from an upset caused by wingtip vortices

The NTSB accident report is not yet available.

Following paragraph cut and pasted from Avflash, Vol. 8, Issue 44b, Thursday, October 31, 2002:

HEAVY RUDDER USE BLAMED IN CRASH: Vigorous use of the rudder is being blamed for the crash of an American Airlines Airbus last November even though company officials and the NTSB may have known excessive rudder use could cause the airframe to fail. Documents released at the first day of the public hearing into the crash of Flight 587 revealed that both Airbus and American officials warned of the potential danger. The tail broke off and the plane crashed shortly after takeoff from Kennedy International Airport Nov. 12 last year killing all 260 on the plane and five more on the ground. Airbus said the tail was subjected to 1.9 times its rated stress load and was certified to take 1.5 times that. In February, the NTSB warned all airline pilots not to use too much rudder to recover from upsets.

More information on this accident is given earlier in these notes at the end of the section on Aerodynamics. In addition, visit


for NTSB, Boeing, and Airbus Industrie documents on this accident.



American Airlines Flight 191 at Chicago O’Hare, May 29, 1979

Information Collected from AirDisasters.com and Submitted by Andrew Sciami (Edited by R. Rogers)

American Airlines Flight 191, a DC-10, was cleared for take off at a weight of 379,000 pounds. Everything was normal during its run until, 6000 feet down the runway and just before rotation, the port engine (No.1) lost power and pieces of the pylon started to fall away from the aircraft. White vapor began to stream from the mounting, caused by fuel spilling from broken fuel lines. A few moments later the entire engine and pylon tore loose and toppled back over the wing and onto the tarmac behind the aircraft. As the DC-10 lifted off, the port wing dropped slightly, but this was soon corrected, and the aircraft climbed out steadily, seemingly unaffected by the loss of one of its engines.

Ten seconds later and at a height of around 300 feet the aircraft began to bank to the left. The bank quickly steepened, the nose dropped, and the aircraft started to lose height. Finally the wings went past the vertical and the aircraft was beyond recovery. The port wingtip struck the ground and the aircraft exploded in a mass fireball and disintigrated completely, 90 metres from a huge caravan park that was a few hundred metres from the end of the runway. Two residents of this park were killed in the carnage, along with the 271 on board the aircraft.

Under normal circumstances an aircraft losing an engine would be able to fly on the remaining power plants still functioning, so why was this accident

different? When the engine separated, it took a 3-foot section of the wing with it, ripping out vital hydraulic and electric lines in the process. The starboard slats stayed extended but the port slats retracted because of the leaking fluid, causing a stall. The crew was unaware of the retraction due to the fact that the no.1 generator powered the Captain's instrument panel, and thus the slat disagreement system. The stick-shaker had also been disabled.

On recovery of the engine/pylon assembly, it was discovered that there was a 10-inch fracture on the rear bulkhead on the pylon. Eight weeks before the accident, the aircraft went through a major check and the self-aligning bearings on the bulkhead to wing attachment joints were changed. Normal procedures would involve removing the engine and pylon from the wing separately, by use of a special cradle to lower the engine, but to save on time, a new idea was adapted using a forklift truck to take the whole assembly off


as one unit. This did not prove to be a good idea because of down travel on the forks. When the assembly was being put back on to the wing, a disagreement occurred between the mechanic and the forklift driver, and a sound like a gun shot was heard, which resulted in the flange on the pylon bulkhead fracturing. Unknown to the mechanics, the aircraft was put back into service with a weakened pylon assembly that seemed to be OK until that fateful afternoon when it failed under normal load conditions.

Readouts from the FDR showed that the No. 2 and 3 engines remained at a high RPM setting after the departure of the No. 1 engine and both right aileron and right rudder were being used to control the aircraft.

The aircraft accelerated to 172 knots before slowing to 159 knots at the time of beginning to roll left. The aircraft hit the ground banked to the left 112 degrees at a 21-degree nose-down attitude. Metallurgical examination of the No. 1 engine pylon showed a stress crack in the upper rear bulkhead flange.

This fracture at this crack would have imposed excess loads on the remaining bulkhead flanges, causing separation. The shape of the fracture resembled the radius of the wing clevis fitting to which it was fitted, suggesting that the flange had been cracked while the engine pylon was being removed or reinstalled on the wing during maintenance. Investigation showed that the No.1 engine and pylon had been removed eight weeks prior to the accident.

This finding caused the FAA to ground all US DC-10s for inspection, which revealed that six more aircraft had similar fractures, four of them belonging to American and the others belonging to Continental. McDonnell-Douglas recommended that the engine be removed first and then the pylon during servicing,

but both American and Continental had been removing and installing the unit as one piece.

Although investigators believed they had discovered the cause of engine separation, there was no reason why aircraft control should have lost with the loss of thrust from the missing No. 1 engine. However, in physical separation of the engine as opposed to an engine ceasing operation, the engine-driven systems associated with that engine are lost because the lines are severed. Upon losing the engine, 191 also lost it's No. 1 hydraulic system and No. 1 AC generator.

The engine separation further severed electrical wiring, resulting in loss of power to the captain's instrument panel and the stall warning system. In addition, four other hydraulic lines and two cables were severed, the hydraulic lines operating the port leading edge slat control valve and the actuating cylinders which push the slats out. The control valve was backed up by the No. 3 hydraulic system, but when the lines were severed, the fluid in the cylinders leaked out, allowing the slats to slowly retract. Because of the loss of electrical power, the slat disagreement system was also inoperative, giving the crew no alert that they were retracting. The loss of the leading edge slats on the port wing increased its stall speed to 159 knots, the speed at which the aircraft began its fatal left roll.

The irony of this accident is this: The crew was following engine-out procedures meticulously. The First Officer pitched the nose up to slow the aircraft to American's prescribed engine-out climb speed, V2+6,


159 knots. Had either the slat disagreement system or the stall warning system been operative, there is a chance they could have taken action to prevent the accident. Simulator tests showed that the aircraft could have been flown and returned safely at speeds above 159 knots.

On finding this fracture of the flange, the FAA took the step of grounding the DC-10 on U.S. registrations pending fleetwide inspections. The inspections revealed that no less than six supposedly serviceable DC-10s had fractures in the upper flanges on the rear of their pylon bulkheads; four American Airlines aircraft and two Continental aircraft.

The evidence showed similar problems in all of the cases found. All of these aircraft had recently had engines changed using the fork truck method. Both airlines had adapted this method as a way of saving time. McDonnell Douglas were advised

first about it, and they did not stop the method, but strongly advised against it. They recommended that an engine and pylon should be removed separately, and not as a whole unit. N110AA was one of the series 10 McDonnell Douglas aircraft whose entire structure had been thoroughly scrutinized and updated after a number of accidents involving the type in the early 1970s. The cockpit was fitted with every available electronic fail-safe mechanism, and all aircrew underwent hours of training in the simulator, learning to cope with any emergency with automatic fluency. So it was with bafflement that investigators from McDonnell Douglas and the FAA began sifting through the wreckage for a cause.

Accident Contributing Factors

The vulnerability of pylon attachment points during maintenence, and of the leading edge slat system that produced asymmetry.

Deficiencies in the FAA's surveillance and reporting systems in failure to detect improper maintenence procedures.

Deficiences in communication between the aircraft operators, McDonnell Douglas, and the FAA in failing to provide details of previous maintenence damage.

Crew procedures to cope with unique emergencies.

Reference: http://www.airdisaster.com/investigations/aacrash.shtml


http://www.airdisaster.com/investigations/aacrash.shtml

Trans World Airlines B727 near Saginaw, Michigan on April 4, 1979

(Verbatim from NTSB Accident Report)

Information Collected and Edited by Kevin Tesch

Bold text indicates verbatim transcription from NTSB report.

See NTSB-AAR-81-08: http://amelia.db.erau.edu/reports/ntsb/aar/AAR81-08.pdf

Scheduled 14 CFR Part 121 operation of Air Carrier TRANS WORLD AIRLINESAccident occurred April 4, 1979 near SAGINAW, MI

Aircraft: Boeing 727-31, registration: N840TWInjuries: 0 Fatal, 0 Serious, 89 Minor/None

Summary

On April 4, 1979, a Trans World Airlines, Inc., Boeing 727, operating as Flight 841, entered an uncontrolled maneuver at 39,000 feet pressured altitude near Saginaw Michigan due to an asymmetrical slat deployment. The aircraft descended uncontrolled to about 5,000 feet before the flight crew regained control. The cause of the asymmetrical slat condition was improper use of the controls by the flight crew, and roll recovery was only possible after the slat tore off the wing.

Analysis

The Safety Board concludes that the Nos. 2, 3, 6, and 7 slats were extended as a consequence of flightcrew action. Further, that when scheduled to retract by the flight crew, the No. 7 slat failed to retract probably because tensile forces created by aerodynamic loads combined with friction and side forces on the piston rod, caused by misalignment of the slat, exceeded the available retraction force.

The reason for the lack of controllability is the severe disruption of airflow and associated loss of lift that occurs over the wing area aft of the extended slat. The loss of lift creates a rolling moment that exceeds the countermoment the pilot can produce with full deflection of lateral controls. The aircraft will respond to the imbalance of the rolling moments by rolling uncontrollably toward the wing with the extended slat.

The captain in an attempt to neutralize the rolling moment deflected full aileron, and rudder. The captain probably induce a sideslip when the aircraft was at mach 0.79, an angle of attack of 5.7 degrees, and an angle of bank of about 35 degrees to the right. A sideslip angle of about 4.8 degrees to the right could have caused the aircraft to become laterally uncontrollable.

About 2148:25, the aircraft completed 360 degrees of roll while descending to about 21,000 feet. Shortly thereafter, the captain commanded landing gear extension which was accomplished by the first officer (helping to slow the aircraft, and the resulting decrease of control pressure broke the accelerated stall). The aircraft continued to descend rapidly, and it continued to roll until the No. 7 slat was torn from the wing and lateral control was restored (therefore if the slat did not separate from the aircraft control would never have been regained). About 2148:58, the captain regained control of the aircraft at an altitude of about 5,000 feet.

Analysis of the evidence indicated that the uncontrolled maneuver began about 2147:47 with isolation of the aircraft’s No.7 leading edge slat (on its right wing) in the extended or partially extended position. During the preceding 14 seconds, the aircraft had rolled slowly to the right about 35 (degrees) of right bank and was returned to near wings level flight. Thereafter, the aircraft rolled again to about 35 (degrees) of right bank in about 4 seconds. At that time, the aircraft reached a condition wherein mach number, angle of attack, and sideslip combined to reduce the aircraft’s


http://amelia.db.erau.edu/reports/ntsb/aar/AAR81-08.pdf

lateral control margin to zero or less, and the aircraft continued to roll to the right in a descending spiral. During the following 33 seconds, the aircraft entered a second roll to the right during which the No. 7 slat was torn from the aircraft. Control of the aircraft was regained about 2148:58 at an altitude of about 8,000 feet.

Flight 841’s flightpath angles during its descent were calculated from indicated airspeed and rate of descent values. These calculations indicated that the aircraft’s flightpath angle decreased from zero at 39,000 feet to 90 degrees vertically downward near 29,000 feet. The angle then decreased to about 30 degrees downward at 24,000 feet and then increased to 40 degrees downward as the aircraft descended through about 18,000 feet. The angle then increased further to about 80 degrees downward at 11,000 feet, decreased to zero during the recovery, and increased to about 55 degrees upward during the pullup following recovery. The angle decreased to about zero near 11,000 feet.

The Captain’s Report and Actions

The captain stated that he was flying the aircraft on autopilot with the Altitude-Hold mode selected. While he was sorting maps or charts, which were located in his flight bag on the left cockpit floor, he felt a buzzing sensation. Within 2 or 3 seconds, the buzzing became a light buffet, and he looked at the flight instruments. He noticed that the autopilot was commanding a turn to the left with the control wheel displaced accordingly, but he noticed that the attitude director indicator (ADI) showed the aircraft in a 20 to 30 degree bank to the right. The ADI showed that the aircraft was continuing to bank to the right at a slightly faster than normal rate of roll, so he disconnected the autopilot and applied more left aileron control to stop the roll.

According to the captain, the aircraft continued to roll to the right in spite of nearly full left aileron control, so he applied left rudder control in addition to the aileron control. He stated that in spite of the almost full deflection of the left aileron and full displacement of the left rudder pedal, the aircraft continued to roll to the right. He believed that the aircraft was going to roll inverted so he retarded the throttles to the flight idle position, and he stated “we’re going over,” or something to that effect. The aircraft rolled, completely and entered a second roll with the nose down.

After detecting no reaction to the speed brake extension, the captain moved the control handle to the retract position and back to the extend position. Meanwhile the: indicated airspeed needle was moving rapidly toward its limit and he could see only “black” on the ADI and bright areas in the windshield which he perceived to be the lights of towns shining through the undercast. The altimeter indicated such a rapid descent that it was difficult to read. However, he estimated that the aircraft was near 15,000 feet and descending rapidly when he commanded extension of the landing gear. The first officer immediately moved the gear handle to the “extend” position, and the flight crew heard a very loud sound similar to the sound of an explosion.

The captain stated that he applied full left aileron and full left rudder throughout the descent but the aircraft continued to roll to the right. Simultaneous with the gear extension, he relaxed some back pressure on the control column and some of the pressure on the aileron and rudder controls (effectively recovering from the accelerated stall). The airspeed began to slow, and he was able to roll the aircraft to a near wings-level attitude and to stop the aircraft’s descent, after which the aircraft pitched upward into a 30 to 50 degree climb. He saw the moon in the windscreen and used it as a visual reference to maneuver the aircraft. The aircraft slowed rapidly, and with guidance from the first and second officers, he leveled the aircraft near 13,000 feet.


NTSB Findings

The Safety Board determines that the probable cause of this accident was the isolation of the No. 7 leading edge slat in the fully or partially extended position after an extension of the Nos. 2, 3, 6, and 7 leading edge slats and the subsequent retraction of the Nos. 2, 3, and 6 slats, and the captain’s untimely flight control inputs to counter the roll resulting from the slat asymmetry. Contributing to the cause was a preexisting misalignment of the No. 7 slat which, when combined with the cruise condition airloads, precluded retraction of that slat. After eliminating all probable individual or combined mechanical failures, or malfunctions which could lead to slat extension, the Safety Board determined that the extension of the slats was the result of the flightcrew’s manipulation of the flap/slat controls. Contributing to the captain’s untimely use of the flight controls (full aileron and rudder control allowing the aircraft to enter a side slip) was distraction due probably to his efforts to rectify the source of the control problem.

See NTSB-AAR-81-08: http://amelia.db.erau.edu/reports/ntsb/aar/AAR81-08.pdf



Delta Flight 106 from JFK on 30 March 2000: Crewmember Disorientation

Information Collected from NTSB Documents and Submitted by Randall Ebersole

NTSB Identification: IAD00IA032 . The docket is stored in the (offline) NTSB Imaging System.14 CFR Part 121 operation of Air Carrier DELTA AIRLINES (D.B.A. COMMERCIAL AIRLINE)

Incident occurred Thursday, March 30, 2000 at NEW YORK CITY, NYAircraft:Boeing 767-332, registration: N182DN

Injuries: 225 Uninjured.

HISTORY OF FLIGHT

On March 30, 2000, about 2025 Eastern Standard Time, a Boeing 767-332, N182DN, operated by Delta Airlines as flight 106, was not damaged when it rolled to the right while climbing through 6,500 feet, 15 miles southeast of John F. Kennedy International (JFK) Airport, New York, New York. There were no injuries to the 13 crew members and 212 passengers. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the passenger flight conducted under 14 CFR Part 121. The flight departed JFK destined for Frankfurt, Germany.

The incident occurred during the hours of night over water at about 40 degrees north latitude, and 73 degrees west longitude.

In the cockpit were the certificated airline transport pilot rated captain, first officer (FO), and the international relief pilot (IRP). The FO was the flying pilot and was hand flying the airplane. The auto-pilot was not engaged. Air traffic control (ATC) had cleared flight 106 to fly a heading of 155 degrees after departure, and was then assigned to fly direct to BETTE intersection. BETTE intersection was located 35 nautical miles east-southeast of JFK.

The three crew members were interviewed on April 6, 2000, in Atlanta, Georgia, by a Safety Board investigator.

According to the captain, ATC instructed the crew to proceed direct to BETTE intersection. The captain entered BETTE into the Flight Management System (FMS), hit the "execute" button, and engaged the lateral navigation (L-NAV) mode on the flight director, which showed a left turn about 20-25 degrees. He then turned his attention to organizing his departure and en route charts.

Shortly after, the FO said something and the captain looked up and saw the FO "wrestling" with the airplane. The captain looked at the attitude director indicator (ADI) and it was "lying on its side" right wing down. The FO had the control wheel in the full left aileron position, attempting to level the airplane.

The captain stated there was a thin deck of clouds about 6,500 feet, and it was a dark night with no moon. He also reported that they were no traffic collision avoidance system (TCAS) alerts or engine indication and crew alerting system (EICAS) warnings

According to the FO, after BETTE intersection was entered into the FMS, he made a control input to follow the flight director, which indicated a left turn. He looked outside the airplane to scan for traffic as the turn was made. He then checked the instruments and the ADI indicated a 60 degree bank turn to the right. He responded with full left aileron followed by left rudder, which returned the airplane to level flight. He stated that from the time BETTE intersection was entered into the FMS, to the time he noted the right bank on the ADI, 5-6 seconds had elapsed.

The FO looked outside the captain's left forward window to scan for traffic. He stated there was no horizon, stars, or moon, and all he saw was darkness. He did not recall seeing any clouds

According to the IRP, he was sitting in the jump seat between the two pilots reviewing the flight plan, when he felt the airplane yaw then roll to the right. He looked up and saw the ADI pointer at 60 degrees right


wing down. At that time, he saw ground lights and a scattered cloud layer below out of the right window. He noted there was no discernable horizon. He saw the FO trying to level the airplane and suggested the use of left rudder to level the airplane.

The airplane was returned to level flight. The crew declared an emergency, dumped 20,000 pounds of fuel, and returned to JFK without incident.

FLIGHT RECORDERS

A Fairchild model A-100 cockpit voice recorder (CVR) was brought to the Safety Board audio laboratory on April 3, 2000. The 30-minute recording was found to have no data relating to the event's period of time; therefore, no transcript was prepared.

Raw data information from the Digital Flight Data Recorder (DFDR) was extracted by Delta Airlines at its playback facility in Atlanta, Georgia, and provided to the Safety Board. According to the Safety Board's DFDR Group Chairman's report:

From 20:24:59 to 20:25:28, the airplane's heading was maintained between 98 degrees and 100 degrees as the altitude increased from 5,100 feet to 6,300 feet.

At 20:25:29, the control wheel began a turn to the right. The right aileron was deflected and the airplane began a roll to the right. The control wheel input continued to increase to the right for the next 3.5 seconds until it reached a peak value of 63.7 degrees right wing down, at which time the bank angle reached 39.4 degrees right wing down. The other flight controls remained steady during this period.

At 20:25:33, the control wheel switched between right inputs and left inputs. The control wheel was manipulated from 63.7 degrees to the right at 20:25:32.5, to 20 degrees left at 20:25:33, then 34 degrees left at 20:25:33.5. At the same time, the elevator was moved to a 2 degree nose down position. The roll angle reached 48 degrees right at 20:25:33.5.

At 20:25:34, the control wheel was switched from a left to right position, and over the next 3-seconds the control wheel was moved between 18.8 degrees right to 40.7 degrees left, trending toward the left by the end of the period. During this 3-second period, the airplane's roll value increased from 62.9 degrees to 65.5 degrees right wing down.

The first indication of a left rudder application was recorded at 20:25:37.3. Over the next 6-seconds, rudder values changed from a steady value of 1.6 degrees right to 4.9 degrees left as the roll angles decreased from 65.5 degrees right wing down to approximately wings level. Also during this period, the control wheel values varied between 3.4 degrees and 34.1 degrees left wing down. With the application of nose up control inputs, the pitch attitude values increased from 5 degrees nose down to 0.9 degrees nose up and the decrease in altitude values stopped.

The DFDR parameters did not display any unusual or anomalous characteristics during the remainder of the flight.

ADDITIONAL INFORMATION

At the time of the event, Delta's B-767 flight operations manual (FOM) addressed unusual attitude recovery procedures in the avoidance and escape section of the manual. According to the unusual attitude recovery procedures, if an upset occurred, the pilot was instructed to roll the wings level. It did not address the use of rudder to assist in the recovery.

During the year prior to this event, Delta had developed a formalized unusual attitude training procedure for their B-767 training manual called Critical Aircraft Situational Training (CAST) maneuvers. This new category of training was implemented on April 1, 2000, and included a 14-minute CAST video, and for the


crews to practice simulated upset recoveries in the simulators. The training manual stated that the use of aileron and coordinated rudder should be used during upset recoveries.

A Federal Aviation Administration Advisory Circular (AC) 60-4A, "Pilot's Spatial Disorientation," conducted tests with qualified instrument pilots. The results indicated that it can take as long as 35 seconds to establish full control by instruments after a loss of visual reference of the earth's surface. AC 60-4A further stated that surface references and the natural horizon may become obscured even though visibility may be above visual flight rules minimums and that an inability to perceive the natural horizon or surface references is common during flights over water, at night, in sparsely populated areas, and in low-visibility conditions.

Source: http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X20649&key=1


http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X20649&key=1

Sky Train Air, Inc Gates Learjet 24 N44CJ on October 1, 1981 Felt, Oklahoma

NTSB #: AAR-82-4: 3 fatal Injuries

Information Collected and Submitted by Greg Craven

Source: http://amelia.db.erau.edu/reports/ntsb/aar/AAR82-04.pdf

Probable Cause: Loss of control, possibly initiated by an unexpected encounter with moderate to severe clear air turbulence, which caused the aircraft to depart the narrow flight envelope boundaries in which it was operating and from which recovery was not effected, the flight crew’s lack of adequate training and experience in the Learjet, and the aircraft’s marginal controllability characteristics near and beyond boundaries of its flight envelope. Contributing to the accident was the flight crew’s probably extension of the spoilers in an overspeed situation, a procedure that had been prescribed in the approved aircraft flight manual until 1 year before the accident.

Key Words: Clear air turbulence, overspeed, stall, buffet boundaries, controllability, mach tuck, aileron buzz, wing spoilers, nose down pitching moment, roll maneuver, high speed dive, spacial certification review.

Airspeed and Spoiler Information Relevant to Learjet 24:

These speeds shall not be deliberately exceeded in any flight condition except where higher speed is specifically authorized for flight tests or pilot training or in approved emergency procedures.

WARNING: Do not extend the spoilers, or operate the spoilers deployed, at speeds above Vmo or Mmo due to the significant nose down pitching moment associated with spoiler deployment.

RECOVERY FROM OVERSPEED

If Vmo or Mmo is inadvertently exceeded:1. Thrust levers – IDLE2. Level wings if required3. Rotate nose – up not to exceed 1.5 g’s

NOTE: If Mmo is inadvertently exceeded to the point where the airplane seems to be out of control, lower the landing gear. The landing gear doors may be lost or damaged, but the main concern is to facilitate recovery by using the extended gear to slow the forward speed of the airplane.

Flight History

On October 1, 1981, while on a return flight to their company headquarters in McAllen, Texas, from Thermopolis, Wyoming, the president of Sky Train Air Inc., the chief pilot, and another company pilot stopped in Casper Wyoming, for fuel. The lineman noted a fuel imbalance when 320 gallons of fuel were added to the left wing and only 260 gallons of fuel were added to the right wing tanks. According to the lineman, the crew was aware of the imbalence. A total of 585 gallons of Jet-A with Prist was supplied which filled the wing tanks to capacity. No fuel transferring was necessary during the refueling. The lineman stated that he believed the fuselage tank was full because the nosegear strut was extended 6 to 12 inches. He stated a ground power unit was used to start the engine and he did not notice any difficulties with the aircraft during the crew’s preflight checks.

Five witnesses at Felt, Oklahoma, located in the southwest portion of the Panhandle, heard an aircraft overhead at a very high speed. One witness stated that he heard a vibration sound which indicated to him the aircraft was overspeeding. Another witness stated that the aircraft was about to break the sound barrier. Of the five witnesses interviewed, only one saw the aircraft – and only momentarily – and he stated the aircraft was in about a 45 degree decent angle and the wings appeared to be rocking up and down. All the



witnesses stated that they heard an explosion and saw a mushroom cloud of black smoke erupt when the aircraft crashed to the ground. The accident occurred at approximately 1502.

The aircraft crashed 2.5 miles southwest of Felt, Oklahoma. This accident location is about 30 miles northwest of another crash site which involved a high altitude loss of control by a Learjet Model 25B.

Analysis

Although the president of the company and the chief pilot were experienced pilots, were rated in the Learjet, and were current to operate the aircraft, both were inexperienced in the Learjet. There was no evidence that indicated the pilot-in-command had any previous experience in turbojet aircraft, other than the 28.3 hours accrued in the Learjet. The chief pilot’s flight experience of 5,000 hours in the DC-8 would have equipped him with sufficient knowledge of high altitude, high speed flight. However, it is doubtful that he had ever operated in the flight regime at 45,000 feet in other aircraft he had previously flown. The third pilot was reportedly a passenger on board, and was not rated in the Learjet and did not have any turbojet experience.

Recommendations

Establish a requirement that manufacturers provide as part of the initial certification of a new general aviation turbojet airplane a training guide for pilot transition into the airplane. The training guide should encompass the entire flight envelope in which the airplane will be operating and any unique aspects of its systems design, handling characteristics, and performance, including the hazards of exceeding the flight envelope. The training guide should be an approved manual for use by appropriate inspectors, pilots, schools, flight instructors, and pilot examiners.

Source: http://amelia.db.erau.edu/reports/ntsb/aar/AAR82-04.pdf



China Airlines Flight 006 B747-SP Accident nearly 300 nautical miles Northwestof San Francisco, California on February 19, 1985

Information Collected and Submitted by Albert Y-Hsiu Chen

NTSB Report Identification: NTSB/AAR-86/03

Full NTSB Report is available at the ERAU Jack R. Hunt Memorial Library, or online at:

http://www.rvs.unibielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html

Scheduled Operations by Foreign Operator, China Airlines of TaiwanAccident occurred on Tuesday, February 19, 1985

about 300 nautical miles northwest of San Francisco, CaliforniaAircraft: Boeing 747-SP, Registration: N4522V

Injuries: 0 Fatal, 2 Serious, 272 Minor or Uninjured.

(Selected parts of the following are pasted verbatim from the NTSB Aircraft Accident Report)

NTSB Synopsis

About 1016 Pacific standard time, February 19, 1985, China Airlines Flight 006, a Boeing 747-SP, enroute to Los Angeles, California from Taipei, Taiwan, suffered an inflight upset. The flight form Taipei to about 300 nm northwest of San Francisco was uneventful and the airplane was cruising at about FL 410 when the No. 4 engine lost power. During the attempt to recover and restore normal power on the No. 4 engine, the airplane rolled to the right, nosed over, and entered an uncontrollable descent. The captain was unable to restore the airplane to stable flight until it had descended to 9,500 feet. After the captain stabilized the airplane, he elected to divert to San Francisco International Airport, where a safe landing was made. The airplane suffered major structural damage during the upset, descent, and subsequent recovery.

NTSB Conclusion

The National Transportation Safety Board determines the probable cause(s) of this accident / incident as follows:

The National Transportation Safety Board determines that the probable cause of this accident was the captain’s preoccupation with an inflight malfunction and his failure to monitor properly the airplane’s flight instruments which resulted in his losing control of the airplane.

Contributing to the accident was the captain’s over-reliance on the autopilot after the loss of thrust on the No. 4 engine.

Summary of the Accident

China Airlines Flight 006 was uneventful until about 300 nautical miles northwest of San Francisco, California. The Boeing 747 was cruising at FL 410 and was above a lower cloud layer whose tops were reported to be about 37,000 feet. The airplane’s autopilot was engaged and was operating in the Performance Management System (PMS), maintaining 0.85 Mach or 254 KIAS.

As the airplane encountered light clear air turbulence, the airspeed began fluctuating between about 0.84 and 0.88 Mach and the PMS began moving the throttles forward and aft to maintain cruise Mach. After several autopilot adjustments, the flight engineer realized the instrument gauges of the No. 4 engine did not indicate a corresponding acceleration as all three other engines were increasing its EPR. Shortly thereafter, the flight engineer told the captain that the No. 4 engine had flamed out. Under the captain’s command, the flight engineer took out the checklist to review the applicable engine out procedures and to ascertain the


http://www.rvs.unibielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html

three-engine enroute cruise altitude, and the first officer was contacting Oakland ATC for a lower altitude request in order to comply with the maximum engine restart altitude (30,000 feet).

When the captain found that the airspeed dropped through 240 KIAS and continued to decelerate, he disengaged the autopilot to lower the airplane’s nose manually in attempt to arrest the airspeed loss. The first officer noted that the airplane had banked slightly to the right, and he notified the captain. The captain said he then looked at his attitude director indicator (ADI) for reference after the airplane had entered the clouds, but he didn’t know what attitude it was in because the artificial horizon line rolled to the vertical position and he suspected the ADI was giving a false indication. The crews felt the airplane entered and abnormal and unfamiliar attitude, and the indicated airspeed continued increasing rapidly until it exceeded the airplane’s maximum operation speed (VMO). The captain started to pull the control column back and the airplane began to decelerate to between about 80 to 100 KIAS and, at that point, he lowered the airplane’s nose, the airplane accelerated and again exceeded VMO. The captain, then assisted by the first officer, pulled the control column back and the airplane decelerated. The captain lowered the nose smoothly, and the airplane began accelerating slowly and as it did so, it emerged from the clouds at about 11,000 feet. Finally, the captain then was able to stabilize the airplane at about 9,500 feet using the horizon as the reference.

According to the NTSB analysis, the captain did not disengage the autopilot in a timely manner, which led to the significant lost of airspeed. As the captain was attempting to regain airspeed by manually lowering the nose, he was concentrating on the airspeed indicator, and failed to detect the airplane’s increasing bank and yaw under the conditions of asymmetrical thrust below the airplane’s minimum controllable speed (VMC).



United Flight 232 at Sioux City, IA on 19 July 1989: Loss of Flight Controls

NTSB Identification: DCA89MA063 . The docket is stored on NTSB microfiche number 39915.14 CFRPart 121 operation of Air Carrier UNITED AIRLINES

Accident occurred Wednesday, July 19, 1989 at SIOUX CITY, IAAircraft:MCDONNELL DOUGLAS DC-10-10, registration: N1819U

Injuries: 111 Fatal, 47 Serious, 125 Minor, 13 Uninjured

Information Collected and Submitted by Tim Hernandez

What follow is for the most part copied verbatim from NTSB AAR90-06. Italics indicate ideas summarized from the AAR, but not quoted verbatim.

Executive Summary

On July 19, 1989, at 1516, a DC-l0-l0, N1819U, operated by United Airlines as flight 232, experienced a catastrophic failure of the No. 2 tail-mounted engine during cruise flight. The separation, fragmentation and forceful discharge of stage 1 fan rotor assembly parts from the No. 2 engine led to the loss of the three hydraulic systems that powered the airplane's flight controls. The flightcrew experienced severe difficulties controlling the airplane, which subsequently crashed during an attempted landing at Sioux Gateway Airport, Iowa. There were 285 passengers and 11 crewmembers onboard. One flight attendant and 110 passengers were fatally injured.

History of United Airlines Flight 232

United Airlines flight 232 a McDonnell Douglas DC-10-10 was a scheduled passenger flight from Denver, Colorado, to Philadelphia, Pennsylvania, with an en route stop at Chicago, Illinois About 1 hour and 7 minutes after takeoff, at 1516:10, the flightcrew heard a loud bang or an explosion, followed by vibration and a shuddering of the airframe. After checking the engine instruments, the flightcrew determined that the No. 2 aft engine had failed. While performing the engine shutdown checklist, the second officer observed that the airplane's normal systems hydraulic pressure and quantity gauges indicated zero. The first officer advised that he could not control the airplane as it entered a right descending turn. The captain took control of the airplane and confirmed that it did not respond to flight control inputs. The captain reduced thrust on the No. 1 engine, and the airplane began to roll to a wings-level attitude.

The captain directed the check airman who was deadheading to take control of the throttles to free the captain and first officer to manipulate the flight controls. The check airman attempted to use engine power to control pitch and roll. The captain stated that about 100 feet above the ground the nose of the airplane began to pitch downward. He also felt the right wing drop down about the same time. The check airman used the first officer's airspeed indicator and visual cues to determine the flightpath and the need for power changes. He continued to manipulate the No. 1 and No. 3 engine throttles until the airplane contacted the ground. He said that no steady application of power was used on the approach and that the power was constantly changing. He believed that he added power just before contacting the ground.

General Characteristics

All of the primary flight controls on the dc10-10 are hydraulically actuated. With the loss of all hydraulic fluid none of the primary flight controls worked. The electrically actuated trim also was not working. The only remaining control that the flight crew had was through the use of secondary flight controls such as differential engine power. A small change in power would typically result in a slight change in speed followed by the appropriate climb or decent and a return to approximately the same trim speed. For UAL 232, the trim speed was set by the airplane configuration and the damage resulting from engine failure and could not be reduced for landing, as is normally the case.


Differential thrust produces a yawing moment and a yaw angle where the airplane is pointed in a direction slightly left or right of the flight path. Because of the wing sweep and dihedral, a yaw angle produces a rolling moment and a roll angle. The roll angle produces the turn to a new heading. For a landing, the elevator and ailerons may produce the required maneuvers in several seconds, which allows for a precise approach to touchdown. For UAL 232, pilot-induced thrust variations were required to control the phugoid and the asymmetric rolling moments attributed to airframe damage, in addition to the maneuvers required for landing. The required maneuvers could be implemented, via thrust variations, with a delay of as much as 20 to 40 seconds. Thus, any thrust changes required for landing would have to be anticipated at least 20 to 40 seconds prior to touchdown, and any required changes within 20 to 40 seconds of landing could not be fully implemented.

Flight Simulator Studies

As a result of the accident, the Safety Board directed a simulator reenactment of the events leading to the crash. The only means of control for the flightcrew was from the operating wing engines. The application of asymmetric power to the wing engines changed the roll attitude, hence the heading. Increasing and decreasing power had a limited effect on the pitch attitude. The airplane tended to oscillate about the center of gravity in the pitch axis. It was not possible to control the pitch oscillations with any measure of precision. Moreover, because airspeed is primarily determined by pitch trim configuration, there was no direct control of airspeed. Consequently, landing at a predetermined point and airspeed on a runway was a highly random event. Overall, the results of this study showed that such a maneuver involved many unknown variables and was not trainable, and the degree of controllability during the approach and landing rendered a simulator training exercise virtually impossible.

Performance of UAL 232 Flightcrew

The primary task confronting the flightcrew was controlling the airplane on its flightpath during the long period (about 60 seconds) of the "phugoid." This task was extremely difficult to accomplish because of the additional need to use the No. 1 and No. 3 power levers asymmetrically to maintain lateral (roll) control coupled with the need to use increases and decreases in thrust to maintain pitch control. The flightcrew found that despite their best efforts, the airplane would not maintain a stabilized flight condition.

The results of simulator experiments showed that a landing attempt under these conditions involves many variables that affect the extent of controllability during the approach and landing. In general, the simulator reenactments indicated that landing parameters, such as speed, touchdown point, direction, attitude, or vertical velocity could be controlled separately, but it was virtually impossible to control all parameters simultaneously.

After carefully observing the performance of a control group of DC-10 qualified pilots in the simulator, it became apparent that training for an attempted landing, comparable to that experienced by UA 232, would not help the crew in successfully handling this problem. Therefore, the Safety Board concludes that the damaged DC-10 airplane, although flyable, could not have been successfully landed on a runway with the loss of all hydraulic flight controls. The Safety Board believes that under the circumstances the UAL flightcrew performance was highly commendable and greatly exceeded reasonable expectations.

Sources: United Airlines Flight 232 NTSB AAR NTSB Accident Report Summary


http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001213X28786&key=1

http://faculty.erau.edu/rogersr/as495/AAR90-06.pdf

VIII. ANNOTATED BIBLIOGRAPHY

Suggestions are invited for additions to this list, which is meager at present

Boeing Airplane Company. Aerodynamic Principles of Large-Airplane Upsets. Web published, n.d. (www.boeing.com/commercial/aeromagazine/aero_03/fo/fo01/story.html)Seminal document in airline upset training. Available at Boeing site and also at AS495L Course Web Site.

Davisson, Bud. “Aerobatics, Does it have a place in training?” Flight Training, July 1998. Not seen by course instructors.

Forsythe, Doug. Airplane Upset Recovery Training. FSF 50th IASS, IFA 27th International Conference and IATA. Washington D. C., November 1997.A conference paper in presentation graphics format discussing the causes and remedies of airplane upsets. Contains numerous figures and diagrams. At the time Forsythe was Manager of Flight safety Programs for the Boeing Commercial Airplane Group.

Goulian, Mike and Geza Szurovy. Advanced Aerobatics. New York: McGraw-Hill, 1997.Not seen by course instructors.

Robson, David. Skydancing Aerobatic Flight Technique. Newcastle, Washington: Aviation Supplies and Academics, 2000.Not seen by course instructors.

www.alliedpilots.orgAllied Pilot’s Association Union (American Airlines) website.

www.alpa.orgAir Line Pilot’s Association Union website.

See also documents &c. available at course web site



http://www.alpa.org/

http://www.alliedpilots.org/

http://www.boeing.com/commercial/aeromagazine/aero_03/fo/fo01/story.html