What happened
On 30 March 2004, a Piper PA-34-200T, registration G-BEJV, was conducting a training flight at Oxford Airport when the nose landing gear collapsed during the final approach. The flight was following an NDB let-down procedure in conditions featuring a 10 kt crosswind.
As the aircraft touched down slightly left of the runway centerline, the nose continued to drop until the underside of the aircraft contacted the runway surface. The impact caused both propellers to strike the ground, which subsequently stopped the engines. The crew, consisting of a commander and a student, managed to bring the aircraft to a halt using the wheelb/brakes. There were no fatalities and no injuries to the two crew members or the single passenger on board.
The investigation
The AAIB examined the aircraft and found that the damage was primarily concentrated on the fuselage front bulkhead and the nose wheel area. Specifically, the investigation identified cracks and distortion in the bulkhead near the actuator attachment point, along with sheared rivets on the mounting structure. This damage indicated that an excessive load had been transmitted through the actuator, a phenomenon that typically only occurs if the drag link is not properly secured in its over-centre position.
Investigators ruled out a hydraulic system failure, as the hydraulic pump, pressure switch, and reservoir were all found to be functioning correctly. Furthermore, the crew had reported the 'three greens' indication, confirming the gear appeared locked in the cockpit. The investigation then focused on the mechanical downlock assembly.
Findings
- The investigation established that the downlock link had suffered distortion at its upper eye end.
- This distortion caused the internal slot to elongate, creating a burr at the upper edge.
- The presence of this burr caused the spring-end washer to rest on the burr rather than the pin shank, compromising the stability of the mechanism.
- The failure of the downlock mechanism to maintain the over-centre position was the primary cause of the gear collapse.