History of Flight
The aircraft, a Piper PA-34-200T Seneca registered G-BNEN, was scheduled for a training flight from Oxford Kidlington Airport. After taxiing to the runway and receiving takeoff clearance, the aircraft entered the runway, lined up, and stopped. The pilot advanced the throttles to achieve 2,000 rpm on each engine, at which point the nose landing gear collapsed. The collapse caused significant damage to both propellers and shock loading of both engines. Both occupants, who were uninjured, evacuated the aircraft through the forward and rear doors.
Damage and Investigation
The lower section of the nose landing gear moved aft during the collapse, damaging the bulkhead and the lower nose landing gear mount behind it. Significant disassembly of the lower forward fuselage was required to access the mount. Examination revealed that all rivet heads on the lower mount were sheared off. The shank sections of the lower rivets indicated they had failed during this collapse, but discoloration of the remnants of the upper four rivet shanks suggested they had failed earlier.
The upper crossplate exhibited a crack through all four rivet holes, with forward-most holes showing deformation. The right side keel beam had cracked between its web and lower flange, extending 18 cm aft from its forward edge. The landing gear support frame and drag links showed no deformation, though the downlock link had some cross-pin slot deformation.
Analysis
The cracking and discoloration indicated that damage to the mount and supporting structure likely originated from a previous nose landing gear collapse on 22 February 2003. After the aircraft was returned to service, the damage probably progressed progressively, overloading further rivets and causing crack propagation in the upper crossplate and right keel beam. This increased flexibility in the lower mount may have affected the downlock mechanism, allowing the drag link to move from its over-center position and leading to the collapse.
A review of the Piper Seneca maintenance manuals revealed no data highlighting the possibility of damage behind the bulkhead or requiring inspection of that area after a nose gear collapse. An access panel in the area allowed visual inspection of the lower mount's lower fasteners, but the upper fasteners could not be readily viewed. Tests on another aircraft confirmed that the condition of the upper fasteners could not be assessed through the access panel.
Conclusions
It is likely that the nose landing gear collapse resulted from the progression of undetected and undetectable damage to the fasteners securing the landing gear lower mount, precipitated by the previous collapse in February 2003. The condition of the internal structure after the earlier collapse gave no indication of damage to the lower landing gear fasteners, and no specific requirements existed to dismantle the structure for inspection.
Safety Action
In response to the findings, New Piper Aircraft Incorporated confirmed they would publish amendments to all PA-34 Seneca series aircraft maintenance manuals, introducing in-situ inspection procedures for damage to the lower nose landing gear mount, surrounding structure, and fasteners following a nose gear collapse. No formal safety recommendations were considered necessary.