What happened
On July 5, 2014, a Socata Rallye 235GT, registration D-EVKL, was performing its fifth and final glider tow of the day at the Puimoisson aerodrome. During the landing roll on runway 08, the pilot experienced significant shimmy. This vibration caused the nose landing gear wheel spindle to fracture. As a result, the aircraft veered to the left, departing the paved portion of the runway. The impact of the failure caused the nose gear leg to break, and the aircraft eventually came to a halt on the grass portion of the runway. There were no injuries reported.
The investigation
The BEA investigation focused on the structural integrity of the nose gear and the maintenance history of the aircraft. Investigators determined that the wheel spindle had failed due to fatigue cracking, although the specific origin of the crack could not be identified.
During the inspection of the aircraft's maintenance records, it was discovered that the shock absorber installed on the landing gear was not the model recommended by the manufacturer. While the maintenance facility had identified this discrepancy during a previous inspection in March 2014 and advised the owner to replace it, the change had not been implemented. Furthermore, while a service bulletin (BS150-32 rev2) required inspections of the spindle every 500 flight hours to prevent fatigue failure, the aircraft had only completed 164 hours since its last inspection. The investigation also noted that the pilot had experienced shimmy in this specific aircraft previously, and a visual inspection of the anti-shimmy system conducted a few days prior to the accident had shown no abnormalities.
Findings
- The primary cause of the failure was a fatigue fracture of the nose gear wheel spindle.
- The installation of an unauthorized shock absorber, which differed from the manufacturer's specifications, may have negatively impacted the mechanical behavior of the spindle under repeated stress.
- The existing maintenance program did not sufficiently account for the high number of landing cycles associated with glider towing operations. An adaptation of the inspection intervals would have better addressed the increased fatigue caused by frequent landings per flight hour.