What happened
On April 14, 2002, at approximately 12:45 local time, a Morane Saulnier MS-880-B, registration EC-FLL, departed from Reus Airport in Tarragona, Spain, for a local pleasure flight. During the takeoff roll, the pilot noticed a slight vibration, which was initially suspected to be a tire puncture or contact between the main gear fairing and the runway.
After approximately 30 minutes of flight, the pilot returned to Reus Airport to land on runway 25. Upon touchdown, the pilot realized the nose wheel was missing. To mitigate the impact, the pilot maintained a high nose attitude, shut down the engine, and allowed the aircraft to taxi without braking until the nose gear assembly made contact with the ground. The pilot sustained no injuries, and the aircraft suffered only minor damage to the nose wheel bearing.
The investigation
An inspection of the detached nose wheel revealed that the tire had shifted approximately 35 degrees relative to the rim, nearly shearing the valve. While low inflation pressure may have caused this displacement, it was not considered the cause of the detachment. The investigation focused on the studs connecting the rim to the bearing, which showed signs of wear and sheared thread remnants.
Technical analysis of the studs and nuts suggested two possible failure mechanisms related to improper torque during maintenance:
- Excessive torque: If the nuts were over-tightened, the threads may have been damaged during assembly, leading the nuts to loosen and eventually fall off during taxiing.
- Insufficient torque: If the nuts were under-tightened, the rim could have wobbled against the nuts during taxiing, creating axial loads that degraded the threads until failure.
Additionally, the investigation noted that the threads on the nuts sheared rather than the threads on the studs. This suggests that the nuts may have possessed mechanical properties inferior to the required specifications, meaning even correct torque could have caused the failure.
Findings
- The nose wheel detached from its housing during the takeoff roll due to improper maintenance or assembly of the wheel components.
- The failure was likely caused by either the application of incorrect torque to the fastening nuts or the use of nuts with substandard mechanical properties.
- The investigation concluded that the wheel had likely been loose for several flight cycles prior to the incident, a condition that could have been identified during a proper pre-flight inspection.