What happened
On 12 January 2007, a BAE Systems Jetstream 4100, registration G-MAJI, was performing a commercial air transport flight departing from Durham Tees Valley Airport. Following a standard takeoff, the crew advanced the engine condition levers to the flight position and applied takeoff power. The aircraft rotated normally and the landing gear was retracted.
While climbing at approximately 400 feet, the co-pilot reported difficulty maintaining pitch control, specifically noting an inability to push the nose down using the control column. The commander took control but encountered similar difficulties. To manage the aircraft's pitch attitude, the crew resorted to varying engine power. After climbing to 7,000 feet, the crew notified air traffic control of the control difficulties and requested vectors for a return to the airport. The aircraft subsequently performed a safe landing with no injuries to the three crew members or three passengers, and no damage was sustained by the aircraft.
The investigation
Engineers from the operating company examined the aircraft and discovered that the elevator manual trim wheel and the engine condition lever friction wheel had become jammed together. Additionally, the electrical elevator trim was non-functional. The investigation established that the friction wheel, which rotates on a common shaft with the manual trim wheel, had made contact with the trim wheel.
Testing revealed that rotating the condition lever friction wheel in the 'tighten' direction caused the two mechanisms to lock. When the wheels were freed, both the manual and electrical trim mechanisms functioned correctly. The investigation also looked into whether a displaced circlip—a known issue addressed in a 1999 manufacturer bulletin—was responsible, but no such displacement was found on G-MAJI.
Findings
- The primary cause of the control difficulty was the mechanical jamming of the elevator manual trim wheel and the engine condition lever friction wheel.
- The jam was triggered when the crew tightened the condition lever friction lock, which caused the friction wheel to move along the shaft and contact the trim wheel.
- The crew's initial belief that the aircraft was simply out of trim led them to avoid using elevator inputs, instead relying on power adjustments to control pitch.
- The investigation concluded that the friction lock had been tightened with more force than normal, causing the physical interference.