AVIATION/ TAILWIND PITCH-UP PROMPTS NTSB ACTION

The June 2008 uncommanded pitch-up of a Boeing 737-400 operated by TAILWIND AIRLINES has resulted in 5 recommendations by the NTSB to the FAA focusing on elevator system redesign for 737-300/400/500 models. The aircraft, registration number TC-TLA, experienced the pitch-up 20ft above the ground on approach to Diyarbakir Airport in Turkey. The NTSB said that the flight crew performed a go-around and controlled the aircraft's pitch with significant column force, full nose-down stabilizer trim and thrust. During the 2nd approach, the crew controlled the aircraft and landed by using forceful control column inputs to maintain pitch control, and sustained injuries during the go-around. The NTSB determined the incident was caused by foreign object debris, a metal roller element from an elevator bearing, that jammed the power control unit on the left elevator. "During its investigation of this incident, the NTSB identified safety issues relating to the protection of the elevator input arm assembly, design of the 737 elevator control system, guidance and training for the 737 flight crews on a jammed elevator control system and upset recovery training," the agency said. Its 5 recommendations focus on those concerns. The NTSB has asked the FAA to require Boeing to develop a method to protect the elevator power control unit from foreign object debris, and mandate that operators modify their aircraft with that method of protection. The NTSB also believes a redesign of the -300-500 series elevator system to prevent a single point jam from restricting the movement of the system is necessary and that operators should be required to implement the new design. The NTSB pointed out that no override mechanism existed on the incident aircraft, and while the Pilots exerted enough force on the control columns to override the jam, the NTSB is "concerned that other jam scenarios may exist in which Pilot inputs would not be enough to successfully control the airplane". The NTSB also said that Boeing needs to develop recovery strategies - checklists or memory items - for 737 models lacking a mechanical override for a jammed elevator in the event of a full control deflection of the elevator system. The Tailwind flightcrew did not have time to reference the 737 flightcrew operations manual or the quick reference handbook, the NTSB said, and its review revealed no checklists or procedures from uncommanded elevator deflection or a jammed elevator control system in the manual. In addition, the NTSB said that the FDR from the aircraft indicated that once the flightcrew re-established minimum control over the pitching tendency, they turned off the hydraulic power to the flight controls. As a result, its final recommendation is within the recovery strategies it believes Boeing should develop, and that the consequences of removing all hydraulic power to aircraft as a response to any uncommanded control surface should be clarified.