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
737.3The Boeing Company
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
737.4The Boeing Company
Leading Edge DevicesLeading Edge Devices
• 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
737.5The Boeing Company
Leading Edge DevicesLeading Edge Devices
• 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
737.6The Boeing Company
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
737.7The Boeing Company
Trailing Edge FlapsTrailing Edge Flaps
• 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
737.8The Boeing Company
Trailing Edge FlapsTrailing Edge Flaps
• 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
737.9The Boeing Company
Trailing Edge FlapsTrailing Edge Flaps
• 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
737.10The Boeing Company
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
737.11The Boeing Company
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
737.12The Boeing Company
Leading Edge Flap TransitLeading Edge Flap Transit
737.13The Boeing Company
Leading Edge Flap TransitLeading Edge Flap Transit
737.14The Boeing Company
Leading Edge Flap TransitLeading Edge Flap Transit
737.15The Boeing Company
Trailing Edge Flap AsymmetryTrailing Edge Flap Asymmetry
737.16The Boeing Company
Trailing Edge Flap AsymmetryTrailing Edge Flap Asymmetry
737.17The Boeing Company
Trailing Edge Flap DisagreeTrailing Edge Flap Disagree
737.18The Boeing Company
Trailing Edge Flap DisagreeTrailing Edge Flap Disagree