What happened
On 24 November 2002, a Piper PA-28R-180 Cherokee Arrow, registration G-BAPW, was conducting a single circuit flight at Denham Aerodrome to verify the aircraft's condition following its annual inspection. The flight was a private operation with the pilot alone on board.
After an uneventful takeoff from Runway 24, the landing gear was retracted as planned. However, when the pilot selected the gear to the down position during the downwind leg, the three green indicators failed to illuminate. Despite attempts to cycle the gear lever and performing the prescribed emergency extension procedure, the gear failed to deploy. During a flypast of the control tower, air traffic personnel suggested the gear appeared to be down, prompting the pilot to proceed with a landing using full flaps.
Upon touchdown, the right main landing gear partially collapsed. As the aircraft continued its landing roll, the left gear also partially collapsed, causing the aircraft to veer off the left side of the runway. The aircraft eventually stopped approximately 40 metres from the runway edge. The pilot sustained no injuries.
The investigation
The investigation focused on the hydraulic and electrical systems responsible for gear operation. It was noted that the landing gear on this model is operated by a pump driven by a reversible electric motor, held in place by hydraulic pressure.
Upon inspecting the aircraft in a hangar, investigators found that the landing gear circuit breaker had tripped. After resetting the breaker and jacking the aircraft, the gear was cycled. During the third cycle, the electric motor stopped mid-extension. Further testing identified that the solenoid responsible for the landing gear motor was operating intermittently; the motor would only resume running when the solenoid was physically tapped.
Findings
- The primary cause of the failure was a faulty landing gear down solenoid that interrupted the electrical supply to the motor during the in-weight flight extension.
- An intermittent internal short within the solenoid likely caused the landing gear circuit breaker to trip.
- The emergency gravity-extension procedure was unable to overcome the electrical failure affecting the motor's operation during the flight.