What happened
On 28 October 1999, a Piper PA-34-200-2, registration G-EXEC, was performing a private positioning flight when it landed at Stapleford Airfield. The aircraft touched down on the tarmac section of Runway 2BB with full flaps and full aft elevator applied. While the main wheels made a soft contact, the nosewheel subsequently lowered into contact with the runway surface.
Following the impact, the pilot immediately shut down both engines and the electrical system, closing the fuel cocks to secure the aircraft. The aircraft slid along the runway before coming to a stop. There were no injuries to the single occupant on board.
The investigation
Investigators examined the nose landing gear and found that the upper, adjustable, eye end of the lower downlock link assembly had broken at its threaded portion. The investigation revealed that the failure occurred during a single bending overload event. Evidence of high compressive axial loading was also present, characterized by severe bearing crushing on the upper edge of the link's aperture and a bent cross-pin.
Analysis of the landing gear geometry showed that the mechanism is susceptible to high compressive loads. The investigation noted that the downlock link had been newly installed only five flights prior to the accident, making it difficult to determine the exact pre-collapse rigging state. However, the findings highlighted that the failure of the downlock link assembly was consistent with high compressive loads being applied to the mechanism.
Findings
- The nose landing gear collapsed due to a bending failure of the upper eye end of the lower downlock link.
- The investigation identified that the PA 34 Seneca type has a statistically higher rate of nose landing gear collapses compared to similar light twin aircraft.
- The downlock mechanism is vulnerable to "hammering" loads, particularly when operating on rough surfaces, which can cause crushing damage to the downlock link slot.
- Inconsistencies and ambiguities were noted in the manufacturer's service manual regarding the rigging procedures and the required over-centre travel measurements.