What happened
On 8 May 2003, a Piper PA-3/4-200T Seneca II, registration G-ROLA, was involved in a ground accident at Sherburn-in-Elmet Aerodrome in Yorkshire. The flight was a private training session for a type conversion and multi-engine instrument rating renewal, with the pilot in the left seat and an instructor in the right seat.
After completing necessary pre-takeoff checks, the pilot taxied the aircraft toward Runway 29. While moving at a groundspeed of approximately 5 to 7 kt, the nose landing gear suddenly collapsed. The aircraft slid roughly 30 feet before coming to a halt with the nose and both propellers in contact with the ground. There were no injuries to the two occupants, who evacuated the aircraft via the main door.
The investigation
The AAIB investigation focused on the mechanical state of the nose gear assembly. The aircraft had a history of recent maintenance, including repairs following a previous accident in 2001. Investigators found that the drag link had been over-tightened during reassembly, which created enough friction to prevent the gear from moving freely into the over-centre position. This friction had been noted during previous flight tests where the gear failed to lock properly during free-fall tests.
Further examination of the downlock spring link revealed that the adjustment lock-nut was loose and the slot through which the cross-pin passed had been enlarged. This enlargement prevented the spring from applying the necessary force to maintain the link's length. While the microswitch incorrectly indicated the gear was 'down and locked', the physical geometry of the drag link remained in an under-centre condition, making the gear vulnerable to collapse under load.
Findings
- The primary cause of the nose gear collapse was a mis-rigged downlock spring link.
- The drag link assembly had been over-tightened, hindering the gear's ability to reach the over-centre position.
- The downlock spring link was not adjusted to the correct length, and the loose lock-nut indicated improper installation.
- The enlargement of the slot in the spring link prevented the spring from effectively maintaining the required tension.