737.1 Flight Controls Design Changes and Checklists Terry Sheehan 737NG Procedures Manager Boeing Commercial Airplanes May 2004 The Boeing Company 737.2 Flight 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 Baacckkggrroouunndd The Boeing Company 737.3 Leading Edge Devices • Leading edge device lockouts occur due to excessive fluid flow – The system sets hydraulic fuses and stops further motion Loocckkoouuttss The Boeing Company 737.4 Leading 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 Loocckkoouuttss The Boeing Company 737.5 Leading 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 Deessiiggnn Chhaannggeess The Boeing Company 737.6 Trailing Edge Flaps • Trailing edge flap lockouts occur due to – Sticking position transmitters – Inadvertent torque brake actuation Loocckkoouuttss The Boeing Company 737.7 Trailing 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 Loocckkoouuttss The Boeing Company 737.8 Trailing 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 Loocckkoouuttss The Boeing Company 737.9 Trailing 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 Deessiiggnn Chhaannggeess The Boeing Company 737.10 Flight 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 nonnormal checklists The Boeing Company 737.11 Checklist 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 The Boeing Company 737.12 Leading Edge Flap Transit The Boeing Company 737.13 Leading Edge Flap Transit The Boeing Company 737.14 Leading Edge Flap Transit The Boeing Company 737.15 Trailing Edge Flap Asymmetry The Boeing Company 737.16 Trailing Edge Flap Asymmetry The Boeing Company 737.17 Trailing Edge Flap Disagree The Boeing Company 737.18 Trailing Edge Flap Disagree
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