What happened
On August 2, 2015, a Mooney 20F, registration F-BOLV, was performing a local flight from Avignon Caumont aerodrome with the pilot and one passenger. During the return portion of the flight, the pilot realized the aircraft's radio was no longer functioning. To maintain communication, the pilot set the transponder to 7600 and utilized a handheld backup radio.
As the aircraft approached for landing, air traffic control requested an aborted approach because the landing gear had failed to extend due to a total electrical failure. The pilot entered the airfield circuit and attempted the emergency manual extension procedure. However, upon touchdown, the landing gear collapsed, causing heavy damage to the aircraft.
The investigation
The investigation focused on the electrical system and the execution of the emergency gear extension. Examination of the wreckage revealed that the battery voltage was below nominal operating levels. The investigation established that the dynamo brushes were heavily worn, preventing proper contact with the commutator. Consequently, the dynamo was not charging the battery or the aircraft's electrical circuit.
Records showed that the pilot had previously experienced electrical issues in June 2015 and had replaced the battery upon returning to Avignon. Although a maintenance check on July 22, 2015, had identified that the dynamo was not charging, the aircraft was flown without the issue being rectified. The most recent 100-hour inspection in January 2015 had checked the generator and accessories but did not reveal any abnormalities because the dynamo was not removed during the inspection.
Regarding the emergency procedure, the pilot performed approximately 50 turns of the manual hand crank. The pilot observed a specific visual indicator between the front seats, which he believed signaled a successful extension. However, the pilot did not recognize the specific alignment marks required by the procedure and did not confirm the gear was locked by cranking the handle until it reached its usual stopping point.
Findings
- The aircraft's electrical system was running solely on battery power, which eventually depleted due to a failure of the dynamo to charge the circuit.
- The landing gear remained unlocked because the pilot performed an incomplete emergency extension procedure, failing to verify the alignment of the visual indicators as required.