Section 14 - Autopilot

7/27/2019 Section 14 - Autopilot

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Section 14

Autopilot

This chapter provides a general introduction to the standard 3-axis autopilot system fitted to themajori ty of BHL AS332Ls. Further reference to BHL FM supp lement No. 12 is necessary forinformation on RNAV coupling and co-pilot mode selection.

For information on the 4-axis system fit ted to a small number of company machines, refer to theFM supp lement 10.15 (section 10). Note that the 4-axis Autopi lot is fundamentally different inseveral respects and a specific EOP checklist is i ssued to each 4-axis aircraft.

Section 14 Autopilot1 of 23


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(After reading this chapter, the look on your face will be)

INTENTIONALLY BLANK


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INTRODUCTION

The SFIM Type 155 Autopilot (AP) is fitted as standard in the Tiger. It is a 3-axis system that providesstability in pitch, roll and yaw each axis being controlled by two mutually monitored lanes. Theprovision of two lanes gives a layer of redundancy in normal operation Lane 1 (the Governing lane)providing inputs to the flying controls and Lane 2 (the Shadowing lane) is used as a comparison toverify integrity of the AP computer signal. In certain failure conditions, one lane alone can provideappropriate inputs.

The Autopilot acts through the autopilot hydraulics unit which provides control inputs in series to the flightcontrol linkages the system having approximately 5% mechanical control authority in pitch and roll, butup to 100% authority in yaw. The hydraulics unit is housed at the base of the broom cupboard (in thebulkhead behind the right-hand pilots seat) and joins the control run immediately downstream of thelower bellcranks. Hydraulic pressure is provided by the left-hand hydraulic system to give assistance tothe pilot in moving the controls. The pressure is reduced from 175 bar to 103 bar and 4.3 bar by the APhydraulic power unit. An isolation (NORMAL-OFF) control is provided via a switch on each pilotscollective lever. The Autopilot control panel is located on the top right corner of the centre console.

The following functions are provided by the SFIM 155 Autopilot:

1. Stability around the Pitch and Roll axes.

2. Gradual variations around the Pitch and Roll axes by use of the 4-way Beep trim switch (alsoknown as the coolie hat) located on each cyclic.

3. Major attitude reference changes in one cyclic axis only (either Pitch or Roll) by Stick and Beeppilot action.

4. Major attitude reference changes in both cyclic axis simultaneously (both Pitch or Roll) by StickTrim Release pilot action.

5. Stability around the Yaw axis.

6. Co-ordinated turns by action of the cyclic stick in roll (airspeed above 60 knots and bank angleabove 4).

7. Directional Attitude Hold and Pedal-controlled turns. (Heading reference will be maintained whenmovement in yaw axis reduces to less than 1 per second.)

8. Fly-through piloting available at all times so that the pilot retains aircraft control, even with thesystem engaged.

In addition, the following higher functions are also available:

(i) Altitude Hold: Aircraft maintains altitude at time of selection.

(ii) Airspeed Hold: Aircraft maintains airspeed at time of selection.

Note - As both these holds are functions of the Pitch channel, only one can be selected at a time.

(iii) Selected Heading Hold: Controlled by heading bug on pilots and co-pilots HSI. The aircraft

will turn (20 bank maximum) onto and will then maintain the heading selected.

The autopilot has two modes of operation: ASE and SAS, depending on the position of a selector switchon the control panel. In SAS mode (Stabilisation Augmentation System), the system ensures short termdamping of aircraft oscillation, without returning the aircraft to its original attitude. In ASE mode(Automatic Stabilisation Equipment) both short term damping and long term attitude stabilisation areensured: the aircraft is returned to the pilots desired attitude.

Note - The higher functions listed above are only available in ASE mode.


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A Note on Stabi li ty & Damping

The helicopter, by nature, is a dynamically unstable machine. Whilst the designer will try to produce anaircraft that will fly with the minimum amount of effort from the pilot, external forces (e.g. turbulence) willaffect the flight path and attitude of the helicopter throughout its flight. Without appropriate assistanceand correction, the pilots workload would be significantly increased.

A helicopter without a stabilisation system will be hard work to fly since all aerodynamic forces acting onthe aircraft will affect its attitude and will need to be corrected manually by the pilot. Since the pilot musttry not to over- or under compensate for the required control input, the workload is high and the flightpath variable.


A helicopter that has an SAS-based stabilisation system will damp out any external aerodynamic forces

that tend to deviate the aircraft from the intended flight path. The rate of that deviation is minimised andcorrective inputs are made by the Autopilot computer to maintain the pilots chosen attitude. Such anaircraft flying in a wings-level attitude, which is affected by turbulence, will be returned to a similarattitude, but in a position offset from the original flight path.

A helicopter that has an ASE-based stabilisation system can be flown so that specific flight parameters(such as altitude, airspeed etc) are corrected for and maintained even though external forces causedeviations from the flight path.

Figure 1 Autopi lot Damping

Intended flightpath

Intended flightpath


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PRINCIPLES OF OPERATION

Each of the three channels (pitch, roll and yaw) constitutes a slave control based on the followingphilosophy. The Autopilot tries to maintain the aircraft attitude selected by the pilot. This datumattitude is stored as a result of where the pilot positions the cyclic stick or yaw pedals. A sensor detectsaircraft movement away from the datum position and sends an electrical signal based on the amplitudeand rate of change of that movement to the AP computer. This deviation information is compared to thememorised information (i.e. the attitude desired by the pilot the datum) and a corrective output signalrelative to the detected deviation is sent to the servo-controls in the AP hydraulics unit. This outputactuates the flying controls, attempting to re-establish the aircraft at its initial attitude.

AP Computer

DatumReference

FlightServoComparatorSensor

ControlsControls


Feedback loop

Figure 2 Schematic of Autopilot Philosophy

The system assumes that the desired attitude (the datum) is unchanged as long as the pilot makes nophysical input to the cyclic stick or yaw pedals. When an input is made to either of these controls by thepilot, the computers memory goes into synchronisation and waits until a new attitude is selected andthen stores this attitude as the new datum.

The following notes describe the system in the AS332L and then show how they relate to the abovephilosophy.


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System Contro l

The Auto Pilot control panel on the central pedestal is the main interface with the AP system for the pilot.The system can be engaged, disengaged and monitored via buttons and indicating lights on the controlpanel. In the event of malfunction, various functions of the system may be deselected via switches onthe same panel in order to allow continued use. A number of system controls are also located on thecyclic sticks and collective levers.

Figure 3 illustrates the Autopilot control panel and the table opposite gives a description of the functionsavailable on the control panel. The red numbers on the Autopilot panel relate to the numbers in the key.


Figure 3 Autopilot Control Panel

Item Descript ion Function

P R Y

YdP R

Lane

Lane

TEST

RUN

A.S.E. AUTO-TRIM NORM COLL LINK CYCL TRIM

S.A.S. PITCH RELEASEDROLL TURB OFF

6

81

7

OFF

2 9

13

18

17 14 12 10

16 15 11

P

19 20

21 22

543

Individual Button


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1 & 2Push button Lane 1 and Lane 2 Activates Lane 1 and Lane 2 (Pitch, Roll and Yaw)

3Two position push buttons(push-in, push-out)

Activates PITCH channel on Lanes 1 and 2 respectivelywhen lane is engaged


Activates ROLL channel on Lanes 1 and 2 respectivelywhen lane is engaged


Activates YAW channel on Lanes 1 and YAW DAMPERon Lane 2 when lane is engaged

6TEST display window Displays defective sequence numbers after running pre-

flight test

7Red light Flashes during test running sequence

8TEST switch When set in RUN position it actuates a self-test sequence

9

Lighting rheostat Adjusts indicator lighting brightness on control panel

10CYCLIC TRIM RELEASE switch Simultaneously releases trim on pitch and roll channels

when in RELEASED position

11COLLECTIVE LINK switch Inhibits the collective pitch/roll coupling when selected

OFF

12Amber warning light Indicates a malfunction in collective link system Switch

OFF collective link switch

13NORM/TURB switch In TURB assists the elimination of dutch roll by sending

correcting yaw and roll signals

14Amber warning light Indicates a malfunction in the automatic roll trim system

Switch OFF automatic trim roll switch

15AUTO TRIM ROLL/OFF switch Allows engagement of automatic trim function via roll trim

actuators

16AUTO TRIM PITCH/OFF switch Allows engagement of automatic trim function via pitch

trim actuators

17Amber warning light Indicates a malfunction in the automatic pitch trim system

Switch OFF automatic trim pitch switch

18 Two position switch Selects piloting mode. Mode ASE to maintain attitude andstability. Mode SAS to provide stability alone.

19Button Identifier

20Mechanical Indicator Indicates white if the button is depressed (engaged)

21Green Engaged Light Indicates that the channel in engaged and operating

correctly

22Amber Fault Light Indicates that a fault has occurred in that channel.


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DIRECT VERTICAL VERTICAL DIRECTGYRO 1 GYRO 1 GYRO 2 GYRO 2

OFF OFF OFF OFF

ON ON ON ON

FAST SLAVE FAST SLAVE

Figure 4 Autopilot Component Location in the Cockpi t

Central Warning Panel

A.P. A.P. HT

YROG

HigherFunction

HSIHSI

HSI & Rotary Selectorfor setting heading bug in

conjunction with heading hold

IAS ALT HDG RNAV

IAS ALT HDG RNAV

HigherFunction

AP.HTTES

Lane 1

Lane 2

RUN

A.S.E. AUTO-TRIM NORM COLL LINK CYCL TRIM

S.A.S. PITCH ROLL TURB OFF RELEASEDOFF

Autopilot Controland Monitoring

Autopilot HeatSelector


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Other controls found on the pilots and co-pilots cyclic and collective levers are illustrated below.


Figure 5 Flight Control Autopilot Switches

4-Way Beep Trim Swi tch (Coolie Hat)Used to modify pitch and roll reference positions

Stick Trim Release Push-ButtonTemporarily releases the stick force trim Anchoring point

Autopi lo t Disengagem ent Push-Button When pressed both Lane 1 and Lane 2 will be disengaged

To re-engage the autopilot, both Lane 1 and Lane 2push-buttons on the control pane must be pressed.

Autopilot Hydraul ics Isolation Swi tch(Normal =Forward and OFF =Rearwards)

Autopilot BARAN ReleaseTemporarily Releases BARAN reference for Altitude

or Airspeed Hold when button is pressed


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System Components

The Autopilot system comprises several other components, which are illustrated below:

1

2

3

4

5

6


7

8

9

11

10

Figure 6 Location of Autopilot System Components

1. Gyroscope control unit : operating andslaving switches for vertical anddirectional gyros

2. Collective pitch potentiometers ANTICIPATOR (These supplycollective/cyclic channel precontrolsignals to prevent attitude variations dueto collective pitch modifications

3. AP hydraulic servocontrol unit

4. Yaw channel microswitch actuator link

5. Roll channel microswitch actuator link

6. Pitch channel microswitch actuatorlink

(The microswitch contacts open to permitfly-through manual override controlwhilst retaining reference attitudeinformation)

7. No 2 vertical gyro unit(VG2)

transmits pitch and roll attitude data toAP lane 2

8. Autopi lot computer- Receives data inputsfrom peripherals shown here and processesoutput signals to the auxiliary servocontrols inthe AP hydraulic unit. Also houses yaw rategyro which transmits signals to yaw damperlane 2 and a lateral accelerometer

9. No 1 vertical gyro uni t (VG1) transmits pitchand roll attitude data to AP lane 1

10. No 2 gyro magnetic compass (DG2) -Transmits heading data to AP yaw channel lane1

11. Ai r data module (BARAN unit) - Monitorspitot and static pressures from co-pilotssystems and transmits airspeed and barometricaltitude signals to AP computer

12. Flux valve (in tailboom) NOT SHOWNHERE. Senses magnetic north and sendssignal to compass control unit to align DG1 andDG2


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Rear View Front View

54 10

6

Pressure3 9 4.3 Bar

7

2

Pressure


1

4.3 Bar91

8

Figure 7 Components of the Autopilot Servo Pack

Key to Figure 6

1. Servovalves where AP computer makes automatic input to controls.

2. Collective servocontrol output rod (connects to collective/yaw coupler and anticipator)

3. Pitch servocontrol output rod (connects to phasing unit)

4. Pitch channel beeper valve

5. Roll channel beeper valve

Items 4 and 5 operate together when cyclic trim release is pressed and operate independently whenlarge attitude change is required and demanded through the 4-way beep trim switch - coolie hat

6. Roll servocontrol output rod (connects to phasing unit)

7. Yaw servocontrol output rod (connects to collective/yaw coupler)

8. Yaw channel open loop system allows large scale inputs to yaw controls

9. Servocontrol bypass valves isolate servocontrols in the event of hydraulic pressure failure

10. Yaw channel damper


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The Autopilot hydraulic unit contains four auxiliary servocontrols (pitch, roll, yaw and collective) insertedin series in the flight control linkages. They actuate by amplifying the pilots control loads in manualoperation (rather like power steering in a car), and converting AP electrical signals into hydrauliccommands when the autopilot is operating.

Note - There is no servovalve or electrical input to the collective channel in the standardautopilot.

In the absence of hydraulic pressure, the bypass valves (9) in Figure 7 operate and the servocontrols actas simple mechanical relays in the flight control linkage, directly actuated by the pilots control inputs.The controls operate normally, but will feel very heavy to the pilot. (Refer to EOP checklist 5/7) APHYDRAULIC FAILURE.

The AP hydraulic unit does not use full left-hand hydraulic system pressure. A hydraulic power unit(found in the base of the broom cupboard) reduces left-hand pressure from 175 bar to 103 bar for theservocontrols. A further reduction to 4.3 bar is made for the supply to the beeper trim valves (4) and(5)in Figure 7.

The servovalves require extremely pure hydraulic fluid so a 15-micron filter is fitted to the hydraulicpower unit. The filter includes a pop up clogging indicator which is visible through an inspection windowjust above the cockpit floor behind the right-hand pilots seat.

Components & Functions of the Cyclic (Pitch & Roll) Servocontrols

Beeper Valve ElectricalControl Signal

21

Main Rotor InputR

3

103 BarSafety Pin

Servo Valve ElectricalControl Signals

A

4

103 Bar

14

5

B13

6

R12

R

Input Play

P11


78

910Input Play

Pilots Control Input

CFigure 8 Pitch and Roll Servo Control


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Manual Operation with Hydraulic Assis tance.

The numbers in the following text relate to Figure 8. Hydraulic pressure separates the bypass pistons(12) and (14): power actuator chambers (A) and (B) are isolated, and the roller (11) is free within thelimits of the input play. Initially, the distribution slide valve (6) is centred, shutting off the pressure inletlines to the actuator chambers (A) and (B), and the output rod (9) is stationary.

A pilot control input at (P) pivots the input lever (10) around point (C). The motion is transmitted by the

link (8) to the stirrup (7) controlling the distributor slide valve (6). The slide valve pressurises oneactuator chamber and opens the second to the hydraulic fluid return line (The figure shows chamber (A)pressurised and (B) open to the fluid reservoir.)

The power actuator piston moves accordingly. The piston movement tends to re-centre the slide valveby means of lever (10), link (8) and stirrup (7). When the pilot action ceases, the slide valve re-centresand the actuator stops moving. Note that the operation of the auxiliary servocontrols in the AP hydraulicunit is similar to the main servocontrol operation covered in the Flight Controls chapter. Also note that inthe absence of an electrical control input signal, servo valve (5) is inoperative (control vane (4) iscentred).

Manual Operation without Hydraulic Ass istance

In the event of an autopilot hydraulic system failure, the pilot closes off the autopilot cut-off solenoidvalve, simultaneously opening the hydraulic unit supply circuits to the return line. The bypass piston (14)is moved by spring pressure (no longer opposed by hydraulic pressure), locking roller (11) andinterconnecting power chambers (A) and (B). In this configuration, a pilot control input at (P) istransmitted directly with out play by lever (10) to the output rod (9), which is driven with minimum effort inthe absence of opposing pressure in chambers (A) and (B).

In the trim actuator (13) the lower chamber is open to the return line, but the upper chamber is isolatedby the beeper valves. The trim actuator is thus hydraulically immobilised: it cannot move downwardsince cavitation phenomena prevent any increase in the upper chamber volume. This arrangementmaintains the initial anchoring point and the simulated trim loads.

Automatic Operation

The electrical control signal actuates the servo valve (5): the vane (4) moves according to the signaldirection and amplitude. The movement of the vane creates differing pressures either side of thedistributor slide valve (6). The slide valve moves, pressurising one actuator chamber and opening theother to the return line. (The figure shows chamber (A) pressurised and chamber (B) open to the fluidreservoir). The movement of the output rod (9) tends to re-centre slide valve (6) by means of stirrup (7).The output rod motion is not felt by the pilot. When the electrical input signal disappears, the vane (4) re-centres, as does slide valve (6): the servo control stops moving.

Note - For a high amplitude electrical input signal, the Autopilot computer causes a beeper valve to open,moving the cyclic stick and modifying the stick anchoring point.


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Components & Functions of the Yaw Servocontrol

1 2

103 Bar

Control Signal

Servo Valve

DistributorSlide ValveR

7

9

C10P

Input play (a)

12

6

5

4

A

B

103 Bar

Figure 9 Yaw Servo Control



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Manual Operation wi th Hydraulic Assistance

A pilot control input at (P) causes lever (10) to pivot around point (C), since the servocontrol actuator isinitially immobilised. Lever (10) first moves freely moving roller (6) within the limits of the open loop play(a), then compresses spring (4), causing the pilot to feel a control load inversely proportional to theaircraft turning radius (i.e. a tight turn produces a heavy control load). The remaining operation sequenceis the same as for the cyclic servo channels: stirrup (7) moves the distributor valve off centre,pressurising one actuator chamber and opening the other to the return line. The movement of the output

rod (9) tends to re-centre the slide valve and the open loop system (4). The yaw damper (1) slows theinput action of rod (P) in the event of excessive yaw pedal movement.

Automatic Operation

The servo valve drives the power actuator in the same way as the cyclic channel servocontrols. As longas the actuator travel does not eliminate the play (a) in the open loop, the yaw pedals are not affected. Ifthe actuator travel exceeds the input play, the input rod (P) is driven and the yaw pedals follow themotion through the damper action. This input rod (P) movement reinforces the servo valve action byslowing the re-centring action of the distributor slide valve.

Manual Operation without Hydraulic Ass istance

Chambers (A) and (B) are interconnected by the bypass valve piston (12). Roller (6) is hydraulicallylocked. Slide valve (2) is pushed by spring pressure, interconnecting the two chambers in the damper.This allows the pilot to move the power actuator with no input play and with minimal yaw pedal loads.

Note in this configuration the yaw damper protection is removed.


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SUMMARY OF SYSTEM OPERATION IN BRISTOW AS332L


Figure 9 Summary of Pitch and Roll Channel Operation.

How are the required functions of the autopilot provided?

(1) Stability in pitch and roll Vertical gyro signals provide sensing signals to the Autopilotcomputer, which are compared with the datum reference.

(2) Gradual variations in pitch and roll A 1 second input to the 4-way coolie hat changes the pitch

attitude by 2 or the roll attitude by 4 (via the servovalve). This function is known as BEEP TRIMand is available whenever lane one is operating. If the input is of a high magnitude, theservovalve may run out of authority and the AP computer operates the beeper valves in order tomake its input more effectively. (NB - The cyclic will move.) A new datum is generated.

(3) Major changes to pitch and roll attitudes (one axis only) The cyclic should be positioned to the

desired attitude in pitch or roll (the beeper trim actuator spring will provide artificial feel). Thespring pressure can be released by operating the 4-way coolie hat in the direction of theattitude change. This method is known as Stick and Beep. A new datum is generated.

(4) Major changes to pitch and roll attitudes (both axes simultaneously) The Trim Release buttonon the cyclic should be depressed, the cyclic repositioned and the Trim Release button released.All 4 beep valves open during the control input. A new datum is generated.

(5) Collective/Pitch coupling and collective/roll coupling is achieved through the Collective Linkfunction. As the collective is raised, the aircrafts nose tends to want to pitch up and roll left(down and right when collective is lowered). The AP computer sends corrective signals to thepitch and roll channels whenever the collective is moved.

TRIMLOAD

SPRING

SERVOVALVE

VERTICAL GYRO 1 VERTICAL GYRO 2(Normally Governing) (Normally Shadowing)

CYCLICSTICK

MICROSWITCHLINK

TRIMACTUATOR

(100% control authority)SERIES

ACTUATOR(Limited authority)

BEEPVALVE

MAINSERVOCONTROL

Hydraulic Unit

AUTO AP APTRIM LANE 1 LANE 2


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(6) Fly-through piloting The micro switch actuator links operate whenever the pilot makes a controlinput (the beeper trim actuator provides artificial feel) and the beeper trim actuator function istemporarily inhibited. The servocontrol moves the control linkages. The old datum ismaintained.

(7) Stability in yaw The Pilots compass (supplied by DG2) and the yaw rate gyro provide sensingsignals to the AP computer that are compared with the datum reference.

(8) Heading hold and pedal controlled turns The heading provided by DG2 is maintained unless

the aircraft is yawing at a rate of more than 1.5 per second.

(9) Co-ordinated turn function Above 60kts, operation of the cyclic leading to more than 4 rollresults in the aircraft performing a balanced turn. The AP computer uses a lateral accelerometerto calculate the amount of yaw input required. The pilot should leave his feet off the pedals. Ifhe places his feet on the pedals, the yaw micro switch actuator operates and a co-ordinated turnis not performed. The pilot must keep the aircraft in balance himself.

(10) Turbulence function In cases of bad turbulence, external forces may be felt on the tail fin,inducing a roll movement. Selecting the NORM-TURB switch to TURB sends the yawcorrection signal to the roll channel to counter this effect.

(11) Altitude Hold The datum is the altitude at the time of engagement of the ALT hold (sensed inthe BARAN unit) and can be changed by adjusting altitude whilst depressing the BARAN releaseswitch on the collective. The datum altitude is maintained by making corrections via the pitchservovalve, or if large corrections are required, via the beep trim actuator (and the cyclic moves)if the AUTO TRIM is functioning in pitch. ALT hold gives a warning if altitude varies more than150 feet from the datum.

(12) Airspeed Hold - The datum is the airspeed at the time of engagement of the A/S hold (sensedin the BARAN unit) and can be changed by adjusting airspeed whilst depressing the BARANrelease switch on the collective. The datum airspeed is maintained by making corrections via thepitch servovalve, or if large corrections are required, via the beep trim actuator (and the cyclicmoves) if the AUTO TRIM is functioning in pitch. ASI hold gives a warning if airspeed varies bymore than 15kts from the datum.

(13) Selected Heading Hold The datum is the heading set on the HSI bug. Either pilot may selectHeading Hold and the aircraft will respond to the most recent selection. (i.e. control will flip-flopbetween the two pilots if each engages this function in turn.) This function should not be usedbelow 60kts as the co-ordinated turn function will not be available. If a heading correction of

more than 2 is required, the aircraft performs a co-ordinated turn onto the required heading.

For a required heading change of less than 2, the AP corrects the heading by slewing theaircraft in yaw.


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Autopi lot Heating

In order to maintain viscosity of the hydraulic fluid in the AP hydraulic unit, the unit should be kept warmwhen flying in the colder temperatures of the normal operating range. This will maintain normal speed ofoperation of the beeper trim valves and prevent build up of pressure in the yaw damper.

Heating is achieved in two ways:

1: A hot air supply is ducted from P2 bleed heating system into the base of the broomcupboard. It comes on whenever the heater is selected on in the cockpit or cabin.

2: An electrical heating system for the hydraulic power unit, beep trim valves and yawdamper. The heaters take the form of resistors embedded in mats wrapped around theappropriate sensitive components. The resistors are powered by 115V AC and areselected ON via a guarded switch on the centre console marked AP HEAT. Whilst thesystem is selected on and functioning correctly, a green light illuminates in the switch.

Heating is controlled to not exceed 80C. A red warning lightAP.HTis locatedon theCWP to warn of a malfunction.

The electrical heating system is operated in the following way.

Prior to each start-up, the AP HEAT is selected ON.

After start:

a) If the OAT is above 0C, AP HEAT is deselected.

b) If the OAT is between 0C and -5C, AP HEAT should remain ON for 20 minutes.

c) If the OAT is less than -5C on the ground or in flight, AP HEAT should be selected ON.

Heating Resistorsfor


Figure 10 Autopilot Heating System

Heating Beeper valves

Hot Air fromCabin Heating System for

Heating Yaw Damper & Trim Actuator

P2 Air Manifold


19/23


Electrical Power Supplies

A number of different electrical supplies are involved in the AP system. A CB on the appropriate panelprotects each supply.

1XP2B - 115v ac for AP heater resistors

1XP2C - 115v ac for powering VG1 and DG1

2XP2C - 115v ac for powering VG2 and DG2

1XP4 - 26v ac for powering AP Lane 2

2XP4 - 26v ac for powering AP Lane 1

1PP6 - 28v dc for system selection, lighting, beeper trim valve operation and mode selection

1PP5 - 28v dc for system selection and mode selection


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Normal Operating Procedures (NOPs)

Pre-start, the AP HYD switches on each collective lever should be checked in the NORM position. Onthe AP control panel, all 6 channels should already have been selected with the white indicatorsshowing. All switches on the panel should be forward.

The autopilot is engaged immediately prior to flight by pushing the Lane 1 and Lane 2 buttons on the APcontrol panel. Six green lights should illuminate (one in each channel button).

The higher functions (Altitude Hold, Airspeed Hold and Selected Heading Hold) can be selected bypressing the appropriate button. A green light in the button (ALT, ASI or HDG) shows that the modehas been selected. If the mode drops out or is deselected by the pilot (using the same button) an amberMode Warn light flashes in the button for 10 seconds.

The autopilot, when fully operational in flight, is a Hands Off system and will fail passive, i.e. if one lanefails there will be no major loss of control.

The autopilot is normally disengaged as soon as the aircraft has landed and is stable on the ground.The system is disengaged by the button the either pilots cyclic. Any time the autopilot is engaged withthe aircraft on the ground the pilot must keep hands and feet on the controls in order to prevent the

autopilot making corrective inputs to the main and tail rotors.

Pre-flight Tests

Prior to the first flight of the day, the AP system test should be performed. The aircraft should not be ona moving platform.

The autopilot should be engaged via Lane 1 and Lane 2 buttons on the AP control panel. AP hydraulicsshould be selected OFF and the test switch on the AP control panel moved to the RUN position.The test takes about one minute, during which time the lights on the control panel illuminate in sequenceand a red dot flashes in the L.E.D. window. (The test sequence may be inhibited if the nose wheel is not

central.)

At the end of the test, a 0 should appear in the L.E.D. window. The test switch should be reset, the APhydraulics reinstated and the AP released.

If a figure other than a 0 appears then the pilot should take the appropriate action as listed in the FlightManual FM (Section 3).

Prior to every flight, the Beep Trim test should be performed. With Lane 1 engaged, the pilot shouldmake an input on the 4-way coolie hat in each direction (fore and aft, left and right). The input shouldbe large enough to saturate the series actuator and operate the beep trim actuator in the appropriatedirection. The cyclic should move. Movement is cancelled by pressing the Trim Release button on thecyclic.


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Emergency Operating Procedures (EOPs)

With any degradation of the autopilot, the pilot must fly the aircraft with hands and feet on the controlsand should limit collective pitch to 15.5 (see FM section 3). Refer to FM section 2 for IMC FlightEnvelope limitations, which are affected by the serviceability of the AP.

Note - With the Autopilot inoperative all manoeuvres must be made gently.

Visual warnings:

CWP (32) panel warnings: Illuminates for 10 seconds in the event of anautopilot system fault or if the autopilot isdisengaged.

A P

Illuminates in the event of gyro malfunction (inassociation with an amber light on the gyropanel).

GYRO

Illuminates in the event of AP heating unit

overheating (>120C) or resistor short circuit.A.P. HT

Hydraulic sub-panel warning: Illuminates when hydraulic pressureA.P. H.P.at the autopilot hydraulics unit is less than 70bar.

For diagnosis of amber warning lights or other indications of a malfunction on either the AP control panelor the overhead gyro control panel, read the following notes and refer to Section 7 of the EOPs whichoutlines the necessary remedial action.

(See also EOP checks 5/7 AP HYDRAULIC FAILURE and 5/9 J AMMED YAW PEDALS from theHydraulics Section of the checklist.)

Notes on the nature of Autopi lot Failures

General

If a channel input fails, the pilot should deselect that channel on the control panel if is not capable ofbeing restored.

Individual Lane Failures:

When a whole Lane fails, the remaining Lane continues to provide stability, however the input to thisLane is no longer being compared with anything. Pitch, Roll and Yaw channels should be deselected inthe failed Lane. Because of the mechanical authority given to the Yaw channel, pilots must also deselectthe remaining Y or YD channel since it is unchecked and has the ability to move the yaw pedals through100% of their range. The unchecked Pitch and Roll channels have only a limited mechanical authority

and single channels may be left engaged to provide normal stability.

Depending on which Lane fails, certain functions of the AP will be lost.

VG and DG Failures:

Failure of a vertical gyro results in the loss of pitch and roll inputs to one Lane (VG1 for Lane 1 and VG 2for Lane 2). The appropriate VG should be switched off. Certain functions of the AP are lost.

Loss of DG2 means that Lane 1 Y has no input. HEADING HOLD is lost and the pilots compass is nolonger supplied with heading information. DG2 should be switched off. Lane 1 Y should be deselectedand, for reasons given above, so should Lane 2 YD.

A failure of DG1 has no effect on the AP since it only provides heading information to the co-pilots HSI.



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Channel Discrepancies

Remember that when both Lanes are operating, Lane 1 is the governing lane and Lane 2 isshadowing providing comparisons and verifying the Lane 1 input. It is the input to Lane 1 that istranslated into aircraft movement.

If the Pitch or Roll inputs from VG1 and VG2 differ, a warning light appears in the pitch or roll channelselector buttons. The rogue channel must be deselected and the remaining channel allowed tocontinue to provide stabilisation. The EOPs method for diagnosing the rogue channel can beconfusing. Instead, you might consider the following.

By definition, both lanes must be operating for a discrepancy to occur. A rogue signal in Lane 1 willimmediately translate itself into aircraft movement away from the desired trimmed attitude. Deselectionof the appropriate channel in Lane 1 should restore the aircraft to the desired attitude as Lane 2 takesover.

If a rogue signal occurs in Lane 2, no attitude change will be seen at the time of the warning, but if theLane 1 channel is subsequently deselected, the rogue signal from remaining Lane 2 channel will causean aircraft attitude deviation.

A channel discrepancy in Yaw requires no diagnosis since, for reasons stated earlier, both yaw channelsmust be deselected.

BE AWARE: AFTER ANY FAILURE THAT RESULTS IN THE AIRCRAFT BEING FLOWN AP OUT ORIN SAS MODE, AN EXTREMELY POWERFUL YAW/ROLL COUPLE IS GENERATED BY EVENSMALL AMOUNTS OF RIGHT PEDAL INPUT. AFTER A SHORT DELAY, THE AIRCRAFT CAN ROLLVIOLENTLY TO THE RIGHT AND COULD BE DISASTROUS SHOULD THE PILOT NOT REGAINCONTROL OF THE AIRCRAFT IMMEDIATELY.


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How to use the Autopilot and Trim system

If you take nothing else away from this chapter, at least use the following maxims asyou develop your flying technique on the AS 332L.

Provided the Autopilot is engaged and fully serviceable, it is recommended to fly withhands and feet away from controls.

The handling pilot should keep hands and feet on the controls when the aircraft is onthe ground anyway, but especially when the Autopilot is engaged.

When handling the aircraft:

Always trim to required pitch attitude.

Make gradual pitch and roll attitude changes via the 4-way switch on the cyclic.

Major large pitch and roll attitude changes using Stick and Beep method.

It is recommended that the aircraft is trimmed to wings level in roll - especially IMC.

Any turns should be made against the artificial feel springs so that if the pilot becomesdisoriented, letting go of the cyclic should result in the aircraft righting itself to wingslevel again.

Documents

Section 14 - Autopilot