Flight Data Recorder - 10 · DCA13FA131 FDR Factual Report, page 1 NATIONAL TRANSPORTATION SAFETY BOARD Vehicle Recorder Division Washington, D.C. 20594 October 27, 2014 Flight Data

DCA13FA131 FDR Factual Report, page 1

NATIONAL TRANSPORTATION SAFETY BOARD Vehicle Recorder Division Washington, D.C. 20594

October 27, 2014

Flight Data Recorder - 10

Specialist’s Factual Report By Sean Payne

1. EVENT SUMMARY

Location: Flushing, NY Date: 07/22/2013 Aircraft: Boeing 737-700 Registration: N753SW Operator: Southwest Airlines NTSB Number: DCA13FA131

On July 22, 2013 about 1740 EDT, N753SW, Boeing 737-700, operated by Southwest Airlines as flight 345, landed hard and sustained a collapsed nose gear on runway 04 at LaGuardia International Airport (LGA), Flushing, New York. Visual meteorological conditions prevailed at the time and an instrument flight plan was filed. Of the 145 passengers and 5 crewmembers, there were 9 minor injuries. The airplane was substantially damaged and there was no fire. The flight was operating under the provisions of 14 Code of Federal Regulations Part 121 as a regularly scheduled passenger flight from Nashville International Airport (BNA), Nashville, Tennessee.

2. FLIGHT DATA RECORDER GROUP

A flight data recorder (FDR) group was not convened.

3. FDR Carriage Requirements

The accident aircraft, N379SW, was manufactured on February 22, 1994, and was operating such that it was required to be equipped with an FDR that recorded, at a minimum, 34 parameters, as cited in 14 CFR Part 121.344(d). 4. DETAILS OF FLIGHT DATA RECORDER INVESTIGATION

The Safety Board’s Vehicle Recorder Division received the following FDR:

Recorder Manufacturer/Model: ALLIED SIGNAL SSFDR 256 WPS Recorder Serial Number: 2472


4.1. ALLIED SIGNAL SSFDR 256 WPS Description

The Allied Signal Solid State Flight Data Recorder (SSFDR) records airplane flight information in a digital format using solid-state flash memory as the recording medium. The SSFDR can receive data in the ARINC 573/717/747 configurations and can record a minimum of 25 hours of flight data. It is configured to record 256 12-bit words of digital information every second. Each grouping of 256 words (each second) is called a subframe. Each subframe has a unique 12-bit synchronization (sync) word identifying it as either subframe 1, 2, 3, or 4. The sync word is the first word in each subframe. The data stream is "in sync" when successive sync words appear at proper 256-word intervals. Each data parameter (e.g. altitude, heading, airspeed) has a specifically assigned word number within the subframe. The SSFDR is designed to meet the crash-survivability requirements of TSO-C124.

4.1.1. Recorder Condition

The recorder was in good condition and the data was extracted normally as per the manufacturer’s procedures.

4.1.2. Recording Description

The FDR recording contained approximately 27 hours of data. Timing of the FDR data is measured in subframe reference number (SRN), where each SRN equals one elapsed second. The event was the last flight of the recording and its duration was approximately 1 hour and 54 minutes. The parameters evaluated for the purpose of this report appeared to be in accordance with the federal FDR carriage requirements. 4.1.3. Engineering Units Conversions

The engineering units conversions used for the data contained in this report are based on documentation from the aircraft operator and manufacturer. Where applicable, the conversions have been changed to ensure that the parameters conform to the NTSB’s standard sign convention that climbing right turns are positive (CRT=+).1

Appendix A lists the FDR parameters verified and provided in this report.

4.2. Time Correlation

Correlation of the FDR data from SRN to the event local time, Eastern Daylight Time (EDT), is referenced in the ‘Cockpit Voice Recorder – Factual Report’.

Accordingly, the time offset for the event flight data from SRN to local EDT is the following: EDT = SRN – 34,066. Therefore, for the rest of this report, all times are referenced as EDT, not SRN.

1 CRT=+ means that for any parameter recorded that indicates a climb or a right turn, the sign for that value

is positive. Also, for any parameter recorded that indicates an action or deflection, if it induces a climb or right turn, the value is positive. Examples: Right Roll = +, Pitch Up = +, Elevator Trailing Edge Up = +, Right Rudder = +.


4.3. Determination of Pilot Flying (PF)

The values for four parameters recorded on the Flight Data Recorder (FDR), Control Column Force Local and Foreign as well as Control Column Position Local and Foreign, were examined to determine the Pilot Flying (PF) while the aircraft was on approach to Runway 04 at KLGA, Flushing, NY. In order to perform this study, two factors must be resolved. First, the active Flight Control Computer (FCC) in use must be determined and second, the column forces and column position data recorded to the FDR must be baselined. Once a determination was made about which FCC computer was in use, the parameters for Foreign and Local column forces could then be defined to either the Captain’s or First Officer’s side. Looking at the corresponding FCC in use, the “local” force data represents the on-side (Captain’s) position and the “foreign” force data represents the First Officer’s side. The values for Control Column Force and Control Column force were then baselined. This was accomplished by studying values for both column force and column position data that were recorded while the aircraft was on the ground prior to departure from KBNA, Nashville, TN. A column neutral position for Control Column Pos-L (Captain) and Pos–R (First Officer) were identified between the time the flight control check was completed (15:37:25 EDT) and prior to the Captain or First Officer touching the controls during takeoff roll (15:49:12 EDT). During this time, the control column remains in a neutral untouched state. The readings for Control Column Pos-L (Captain) and Pos-R (First Officer) during this time interval remain steady at -0.47 and 0.58, respectively. These biases were then offset in the plotting software to return the values to a neutral position of 0. During this time frame (707 seconds), readings for the force transducer varied between -2.88 lbs. and 0.75 lbs for the Captain and -4.69 lbs. and -1.00 lbs. for the First Officer. The average force reading to the each transducer was calculated, -0.84 lbs. for the Captain and -3.03 lbs. for the First Officer, and an offset was applied in the FDR plotting software.

The design of the flight control system provides an interconnected system that allows

movements to be transferred between the Captain’s control column and the First Officer’s control column via a mechanical linkage. There are two control column force transducers for both the Captain’s and First Officer’s control column that allow the applied column force by the PF to be transmitted along the two linkages that connect the columns. After the biases in the parameters were determined and offset (removed) as shown above, the PF can be determined by looking for higher force displacement values in both the Pull (positive direction) and Push (negative direction). A higher reading on either scale would indicate which flight deck officer was actively manipulating the flight controls.

4.4. FDR Plots and Corresponding Tabular Data

Figures 1 to 4 contain FDR data recorded during the 07/27/2013 event. All the parameters plotted are listed in table A-1.

These figures are configured such that right turns are indicated by the trace moving toward the bottom of the page, left turns towards the top of the page, and nose up attitudes towards the top of the page.


Both values for ILS Glideslope Deviation (ILS GS Dev L+R) and ILS Localizer Deviation (ILS Loc Dev. L+R) were converted from DDM to DOTS as per Boeing aircraft documentation. For ILS Glideslope Deviation, a positive sense indicates the aircraft is above glideslope which is translated as a “Fly Down” command. For ILS Localizer, a positive sense indicates the aircraft is left of glideslope which is translated as a “Fly Right” command.

The corresponding tabular data used to create figures 1 to 4 are provided in electronic comma separated value (*.csv) format as Attachment 1 to this report.

Figure 1 describes the aircraft as it begins to intercept the ILS for Runway 04 at LGA through touchdown and rollout. The plot begins at 17:41:00 EDT. The autopilot was engaged and the auto throttles were engaged in Auto Throttle MCP Speed Mode with a selected airspeed of 210 knots as the aircraft’s heading intercepts the LGA Runway 04 localizer. The aircraft begins its descent from the initial approach fix step down altitude of 2,700 feet MSL. At 17:41:14, the MCP Airspeed Select was decreased to a selected value of 180 knots as the aircraft continues to descend on glideslope. The MCP Airspeed Select was then changed two more times, first at 17:41:54 to a value of 150 knots and later at 17:42:36 to 134 knots. The MCP Airspeed Select would remain at 134 knots for the rest of the approach until the Auto Throttle was disengaged for the remainder of the flight at 17:43:49. One second later at 17:43:50, the data shows the autopilot being disengaged and the autopilot is displayed as “not select”. At this moment, the Radio Altimeter shows the aircraft as somewhere between 385 and 361 feet above the ground and a pressure altitude of roughly 470 feet MSL. The aircraft continues the approach as it descends tracking the runway heading of around 044 degrees. Control Column Position data shows the Pilot Flying (PF) actively manipulating the flight controls after the auto pilot was disengaged. Control Column Position Forces describe the First Officer’s column force transducer readings being of a greater value than that of the Captain side in both the push (negative) and pull (positive) directions. Around 17:44:11 EDT, the ILS Glideslope Deviation readings show the beginning of a “Fly Down” trend (aircraft above glideslope) which reaches a maximum at 17:44:23 just before touchdown. Just prior to the maximum recorded glideslope deviation, Control Column Force readings for both the Captain and First Officer appear to have become close in alignment. At 17:44:36, Engine 1 and 2’s throttle resolver angles (TRA) have been decreased to a value of around 35 degrees. The recorded values for Engine 1 and 2 % RPM N1 start to follow a decreasing trend during this time. The aircraft’s pitch has begun to enter a negative (nose down) trend which continues to decrease to a minimum airborne value of -3.87 degrees. Just prior to touchdown, Control Column Position for Captain and First Officer remain near zero. Touchdown occurs at approximately 17:44:27 where the readings for vertical acceleration peaks at 3.18 Gs. Data shows the aircraft coming to rest at 17:44:46.

Figure 2 is an expanded version of Figure 1 and shows the aircraft on approach from a radio altitude of roughly 500 feet through touchdown and rollout. The plot begins at 17:43:40 and shows approximately 75 seconds of recorded data. Specific excerpts from the CVR transcript are overlaid on the plot according to the times in which they were recorded. The time alignment was made in accordance to the values presented in section 4.2 of this report.


Figure 3 shows the movement of the flight controls as the aircraft is on approach below 3,000 Feet. Gear Extension, Touchdown and Runway heading are shown as notes on the plot.

Figure 4 shows the movement of the flight controls as the aircraft is on approach below 500 feet.


APPENDIX A

This appendix describes the parameters provided and verified in this report. Table A-1 lists the parameters and table A-2 describes the unit abbreviations used in this report.

Table A-1. Verified and provided FDR parameters.

Parameter Name Parameter Description

1. AT Engage Auto Throttle Engaged/Disengaged

2. AP Cmd-A Auto Pilot Command Switch - Captain

3. AP Cmd-B Auto Pilot Command Switch – First Officer

4. Accel Vert (g) Vertical Acceleration

5. Ctrl Col Force – Local (Lbs) Control Column Force – Captain Side

6. Ctrl Col Force – Foreign (Lbs) Control Column Force – First Officer Side

7. Pitch-L (deg) Pitch

8. ILS GS Dev-R (dots) ILS Glideslope Deviation – F/O Side

9. ILS GS Dev-L (dots) ILS Glideslope Deviation – Captain Side

10. Eng1 N1 (% RPM) Engine 1 % RPM N1

11. Eng2 N1 (% RPM) Engine 2 % RPM N1

12. Eng1 Throttle Res (deg) Engine 1 Throttle Resolver Angle

13. Eng2 Throttle Res (deg) Engine 2 Throttle Resolver Angle

14. Heading-L (deg) Heading

15. ILS Loc Dev-L ILS Localizer Deviation – Captain Side

16. ILS Loc Dev-R ILS Localizer Deviation – First Officer Side

17. Airspeed Comp (kts) Computed Airspeed

18. Airspeed Sel (kts) Auto Throttle MCP Selected Airspeed

19. Altitude Press (ft) Pressure Altitude

20. Altitude Radio-L Radio Altitude – Left Side

21. Altitude Radio-R Radio Altitude – Right Side

22. Gear WOW-L Weight on Wheels – Left Main Gear

23. Gear WOW-R Weight on Wheels – Right Main Gear

24. Gear WOW-N Weight on Wheels – Nose Gear

25. Flap Handle Pos Flap Handle Position

26. Elevator-L Elevator Position – Left Side

27. Elevator-R Elevator Position – Right Side

28. Time (sec) Time

Table A-2. Unit abbreviations.

Units Abbreviation Description

%RPM percent revolutions per minute

Kts knots

deg degrees

ft feet

g g

DCA13FA131 FDR Factual Report, page A-1

Figure 1. Pitch Control 3000 Feet and Below on Approach


Figure 2. Pitch Control 500 Feet and Below on Approach


Figure 3. Flight Controls 3000 Feet and Below on Approach.


Figure 4. Flight Controls 500 Feet and Below on Approach.

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Flight Data Recorder - 10 · DCA13FA131 FDR Factual Report, page 1 NATIONAL TRANSPORTATION SAFETY BOARD Vehicle Recorder Division Washington, D.C. 20594 October 27, 2014 Flight Data