What happened
On February 9, 2006, a Morane Saulnier MS-893-E, registration EC-CUK, was performing a local flight for aerial photography at Cuatro Vientos Airport in Madrid. The flight was operated by Alfonso Galán and carried a crew of two, consisting of the pilot and a photographer.
During the takeoff roll, shortly after the nose wheel had lifted off the ground, the pilot was notified by the control tower that a component, likely a wheel, had detached from the aircraft. The pilot returned to the airfield and performed a low pass over the runway to confirm the loss of the nose wheel. The pilot subsequently executed a standard approach and landed the aircraft, maintaining the main landing gear on the runway until the final moments of the landing roll, at which point the nose gear strut made contact with the asphalt.
The aircraft sustained minor damage concentrated on the nose gear strut. The two occupants evacuated the aircraft on their own and sustained no injuries.
The investigation
The investigation focused on the assembly of the nose wheel and its connection to the landing gear. The assembly included the tire, two half-rims, a coupling element, and various fasteners such as bolts, self-locking nuts, and washers.
Physical examination of the recovered nose wheel revealed that while the tire and rim remained intact and pressurized, the bolt holes in the rim had become ovalized. The investigation found that the nose wheel axle and the support structure had suffered abrasive damage from sliding on the runway surface.
Analysis of the bolts showed that the fracture surfaces were perpendicular to the bolt axis. While the bolts met manufacturer specifications, microfractographic analysis could not determine the exact nature of the fractures due to surface damage. Crucially, the investigation determined that two of the four nuts on the inner side of the rim remained in place, but the two nuts on the outer side were lost, and no outer nuts were recovered.
Findings
- The loss of the nose wheel was caused by the loss of the fastening nuts connecting the rim to the landing gear coupling.
- The ovalization of the bolt holes in the rim was uniform across all four holes, suggesting that the nuts lost their required torque in a progressive and similar manner.
- The loss of the nuts was likely caused by either the application of inadequate torque during assembly or the repeated reuse of the self-locking nuts, which can degrade their ability to remain secure after multiple assembly/disassembly cycles.