b737 flight controls-design_change

737.1

Flight Controls Design Changes and ChecklistsFlight Controls Design

Changes and ChecklistsTerry Sheehan

737NG Procedures ManagerBoeing Commercial Airplanes

May 2004

Terry Sheehan737NG Procedures Manager

Boeing Commercial AirplanesMay 2004

737.2The Boeing Company

Flight Controls FailuresFlight Controls Failures

• Flight crews have experienced flight control failures in which the leading edge devices or trailing edge flaps fail to move to the commanded position

• Lockout of leading edge devices generally occurs during retraction after takeoff

• Lockout of trailing edge flaps generally occurs during extension while on approach to landing

• Flight crews have experienced flight control failures in which the leading edge devices or trailing edge flaps fail to move to the commanded position

• Lockout of leading edge devices generally occurs during retraction after takeoff

• Lockout of trailing edge flaps generally occurs during extension while on approach to landing

BackgroundBackground


Leading Edge DevicesLeading Edge Devices

• Leading edge device lockouts occur due to excessive fluid flow

– The system sets hydraulic fuses and stops further motion

• Leading edge device lockouts occur due to excessive fluid flow

– The system sets hydraulic fuses and stops further motion

LockoutsLockouts



• Three known causes have been identified: – Debris in the system holds the LE slat pressure

relief valve in the open position – O-ring extrusion in the slat actuator cylinders

allows fluid flow between cylinders– Metallic debris in the auto slat valve (introduced

during valve production) allows fluid to flow to the hydraulic return

• Three known causes have been identified: – Debris in the system holds the LE slat pressure

relief valve in the open position – O-ring extrusion in the slat actuator cylinders

allows fluid flow between cylinders– Metallic debris in the auto slat valve (introduced

during valve production) allows fluid to flow to the hydraulic return

LockoutsLockouts



• The leading edge slat actuator has been redesigned to remove the internal pressure relief valve and to prevent separation of the O-ring

– New design introduced in January 2002– Service Bulletin issued for in-service airplanes

• Production procedures have been changed to significantly reduce the possibility of metal fracture during manufacturing

• The leading edge slat actuator has been redesigned to remove the internal pressure relief valve and to prevent separation of the O-ring

– New design introduced in January 2002– Service Bulletin issued for in-service airplanes

• Production procedures have been changed to significantly reduce the possibility of metal fracture during manufacturing

Design ChangesDesign Changes


Trailing Edge FlapsTrailing Edge Flaps

• Trailing edge flap lockouts occur due to – Sticking position transmitters– Inadvertent torque brake actuation

• Trailing edge flap lockouts occur due to – Sticking position transmitters– Inadvertent torque brake actuation

LockoutsLockouts



• Position transmitters stick due to contamination in the synchronization bearings caused by the improper mixing of two types of lubricants

• The difference in the position information between the left and right indicators results in an asymmetry shutdown

• Position transmitters stick due to contamination in the synchronization bearings caused by the improper mixing of two types of lubricants

• The difference in the position information between the left and right indicators results in an asymmetry shutdown

LockoutsLockouts



• Torque brake activates inadvertently and prevents further movement of the trailing edge flaps

– Occurs with flaps under high load (Flaps > 15)

• A number of failures can be attributed to momentary activation of the flap load relief function

• Torque brake activates inadvertently and prevents further movement of the trailing edge flaps

– Occurs with flaps under high load (Flaps > 15)

• A number of failures can be attributed to momentary activation of the flap load relief function

LockoutsLockouts



• Position transmitters have been reworked by supplier– Warranties have been extended

• Torque brake has been redesigned– New torque brake design was introduced in

production at Line Number 696– “Toothed” torque brake design results in less

internal drag

• Position transmitters have been reworked by supplier– Warranties have been extended

• Torque brake has been redesigned– New torque brake design was introduced in

production at Line Number 696– “Toothed” torque brake design results in less

internal drag

Design ChangesDesign Changes


Flight Crew ImpactFlight Crew Impact

• These design changes have significantly reduced the number of flight control lockouts, but have not entirely eliminated them

– Flight crew must continue to accomplish non-normal checklists

• These design changes have significantly reduced the number of flight control lockouts, but have not entirely eliminated them

– Flight crew must continue to accomplish non-normal checklists


Checklist ChangesChecklist Changes

• Input from operators indicate flight crews were often confused about the proper checklist to use in the event of a flight control failure

• Boeing has worked to delete unnecessary checklists, combine checklists where possible and provide additional clarification

• Input from operators indicate flight crews were often confused about the proper checklist to use in the event of a flight control failure

• Boeing has worked to delete unnecessary checklists, combine checklists where possible and provide additional clarification


Leading Edge Flap TransitLeading Edge Flap Transit


Trailing Edge Flap AsymmetryTrailing Edge Flap Asymmetry


Trailing Edge Flap DisagreeTrailing Edge Flap Disagree

b737 flight controls-design_change

Education

leading edge slat actuator

new torque brake design

new design

open position

position information

valve production

high load flaps

slat pressure relief