What happened
On April 17, 2011, at 16:30 local time, a Socata Rallye MS 893 A, registration F-BRKT, was involved in a ground accident at Itxassou aerodrome. Following the completion of the thirteenth glider tow of the day, the pilot landed on the unpaved runway 26. While taxiing across the paved acceleration strip of runway 08 to reach the fuel pump, the nose gear failed. The aircraft's nose collapsed, causing the plane to travel several meters before coming to a stop in the grass. The incident resulted in damaged propeller and structural damage to the nose gear assembly.
The investigation
The investigation focused on the structural integrity of the nose gear and the airfield conditions. It was noted that the airfield, used primarily for gliding and service aircraft, features a 600 m x 50 m unpaved runway. A physical step or irregularity exists where the unpaved runway meets the paved acceleration strips. The pilot's routine involved landing mid-runway and taxiing across these strips to access the refueling station.
Metallurgical examinations of the broken stay wires revealed welding defects. These defects, combined with corrosion and operational stresses, led to progressive cracking and embrittlement of the gear. The aircraft, which had been in service since 1969, had accumulated approximately 7,500 flight hours. While a dye penetrant inspection in 2004 had not detected cracking, and a 50-hour periodic inspection in January 2011 showed no visible corrosion, the structural failure was traced to the underlying weld flaws.
Findings
- The primary cause of the failure was excessive repetitive stress applied to the nose gear as the aircraft crossed the terrain irregularity between the unpaved runway and the paved strip.
- Metallurgical analysis identified welding defects in the stay wires.
- Corrosion within these weld defects contributed to the progressive cracking and subsequent fatigue failure of the gear components.