What happened
On the night of November 5, 2003, a Socata TB 20 operated by a flight school was returning from a VFR instructional flight. As the trainee pilot prepared to land on runway 22 at Merville, the landing gear was deployed; however, only the nose gear and the right main gear successfully locked in the down position.
Upon realizing the gear was not fully locked, the instructor attempted to retract and then redeploy the gear normally. During this process, the aircraft's alternator failed, prompting the instructor to shed electrical loads and attempt the emergency manual extension procedure via gravity. Despite performing several maneuvers under load to encourage the gear to lock, the instructor could not confirm the status of the left main gear. After consulting with the Merville tower controller, who noted that only the nose gear appeared fully extended, the crew diverted to Lille-Lesquin to access better emergency services.
During the final approach to runway 20 at Lille-Lesquin, the instructor shut down the engine, disconnected the battery, and closed the fuel valve. The aircraft touched down approximately 100 meters past the threshold on the nose gear and the tail skid. The aircraft slid roughly 300 meters along the runway centerline before coming to a halt. There were no fatalities or injuries among the three occupants.
The investigation
The investigation focused on why the left main landing gear failed to lock despite the use of emergency procedures. Examination of the aircraft's mechanical components revealed that the main landing gear drag braces were seized.
Findings
- The primary cause of the gear failure was an omission during a recent maintenance operation.
- During the aircraft's last major inspection, the main landing gear drag braces had been replaced.
- The required lubrication of these new components had been neglected, causing the braces to seize and preventing the gear from locking in the down position.