What happened
On May 25, 1999, a Piper PA-24-260, registration HB-OTF, departed from the Les Eplatures airfield for a flight instruction session focused on autopilot transitions. Shortly after takeoff, the crew, consisting of a pilot and an instructor, experienced a total electrical failure. Due to the loss of power, the crew decided to divert to the Yverle-les-Bains aerodrome, where the aircraft's maintenance provider was located.
During the approach, the instructor took responsibility for the emergency landing gear deployment using the manual backup system, while the pilot maintained control of the aircraft. Although the instructor believed the manual deployment procedure had been completed according to the checklist, they suspected the gear might not be locked and chose not to alert the pilot to avoid increasing cockpit stress. During the landing roll, the landing gear retracted under the weight of the aircraft, causing the plane to slide on its belly for approximately 50 to 60 meters. There were no injuries to the occupants.
The investigation
Investigators examined the aircraft's electrical system and the landing gear mechanism. The investigation found that the onboard battery was completely discharged and could no longer be recharged. While a minor defect was found in the alternator's diode, it was determined that this would not have caused the total battery depletion. The electrical system showed no signs of short circuits.
Regarding the landing gear, the investigation focused on the manual release mechanism located between the front seats. The procedure requires the pilot to decouple the electric motor-driven screw jack by pushing a decoupling lever fully forward before manually extending the gear with a hand crank. Physical examination of the gear assembly revealed that the electric drive jack had not been properly decoupled, which allowed the gear to collapse upon impact.
Findings
- The primary cause of the accident was the incomplete manipulation of the emergency landing gear release system.
- The manual deployment was necessitated by a total electrical failure caused by a depleted or defective battery.
- The instructor failed to push the decoupling lever sufficiently forward, likely because the final stage of the lever's travel requires significant physical effort.
- The failure to fully decouple the electric actuator prevented the gear from locking in the down position, leading to the gear-up landing.