The National Transportation Safety Board last week recommended to the FAA that Boeing be required to develop a method to protect the elevator power control unit input arm assembly on 737-300 through -500 series airplanes from foreign object debris.
The action was the result of a 2009 near loss-of-control incident aboard a Turkish 737-400 operated as Tailwind Airlines, while on approach to Diyarbakir Airport Turkey. At 20 feet above the ground, the crew experienced an uncommanded pitch-up that required significant column force to control the aircraft during the ensuing go-around. The aircraft also required full nose-down stabilizer trim and thrust to control. The aircraft landed safely. While no passengers or cabincrew were injured, the two pilots did.
The NTSB determined the cause to be debris from an elevator bearing that lodged itself in the left elevator power control unit (PCU). During its investigation, the NTSB identified safety issues relating to the protection of the elevator PCU input arm assembly and design of the 737 elevator control system.
In addition to developing a method to prevent this type of elevator jam, the Board also developed guidance and training for Boeing to create recovery strategies for pilots of 737s that do not have a mechanical override feature for a jammed elevator system.