What happened
On June 23, 2015, an ELA 07 gyroplane, registration 34-ACG, departed from the Millau Larzac aerodrome for a local flight. Shortly after takeoff, while climbing and turning left toward the downwind leg, the aircraft experienced a sudden structural failure. Witnesses observed the gyroplane returning rapidly toward the threshold of runway 32, noting that the tail boom appeared partially detached and the aircraft was making an unusual noise. Moments later, the aircraft struck the ground with high impact force, resulting in the death of the pilot and the destruction of the aircraft.
The investigation
The investigation focused on the wreckage located near the start of the paved runway. The debris field was concentrated, with the furthest light component found only eleven meters from the impact point. Investigators found that the engine was still delivering power at the moment of impact.
Detailed examination of the airframe, which consisted of stainless steel square sections welded together, revealed that the rear boom had broken in two distinct locations. Analysis of the welds showed significant manufacturing defects, including irregularities, excessive penetration, lack of penetration, and surface projections. Metallographic testing confirmed that fatigue cracks had initiated at the root of these internal weld defects and propagated outward due to standard operational stresses such as vibration, bending, and torsion. The final separation at the identified break points was caused by structural overload.
Findings
- The primary cause of the accident was manufacturing weld defects within the rear boom of the aircraft.
- These defects led to progressive fatigue cracking under normal flight loads.
- The structural integrity of the tail boom was compromised, leading to a partial separation of the tail assembly during flight.
- Evidence suggested that similar welding flaws were present in other ELA 07 aircraft, including a separate incident involving registration 32-MO in July 2015.
Safety action
Following the investigation, the DGAC issued an airworthiness directive in July 2017 mandating specific inspections of the tail booms for ELA 07 aircraft.