What happened
On July 29, 2015, a Pilatus B4-PC11AF glider, registered F-CINH, was performing an aerobatic demonstration during the Lorraine Mondial Air Ballon airshow at the Chambley-Bussières aerodrome. After being towed to an altitude of 1,450 meters, the pilot released from the tow plane and began a series of maneuvers, including a roll and a half followed by a half-loop.
Following a recovery from a descending flight path, the pilot attempted to initiate a half-loop. During this maneuver, a loud noise was heard and the cockpit canopy shattered. The pilot quickly realized the aircraft was uncontrollable, jettisoned the canopy, and successfully deployed a parachute. During the descent, the pilot observed that the right wing had separated from the fuselage. The pilot landed hard on a paved area of the aerodrome, where the wind dragged them several meters across the ground. The accident resulted in one injury and the destruction of the aircraft.
The investigation
The investigation focused on the structural integrity of the wreckage and flight data recovered from an onboard electronic accelerometer. Examination of the wreckage revealed that the upper spar cap of the right wing had ruptured approximately 100-150 mm from the wing root. The lower spar cap had also detached due to rivet failure, with deformations indicating upward and rearward bending loads. No evidence of fatigue cracking or corrosion was found, suggesting a sudden structural failure.
Data from the accelerometer provided a precise record of the flight loads. While the initial maneuvers remained within safe limits, the data showed that the aircraft''s speed increased significantly during the sequence. The investigation compared these loads against the aircraft's flight manual, which specifies a maximum positive load factor of +7.0 G and a never-exceed speed (VNE) of 240 km/h.
Findings
- The aircraft was operating well beyond its structural design limits during the final maneuver.
- The accelerometer recorded a peak load factor of +9.7 G at the moment of failure.
- The aircraft's speed had reached 270 km/h at the start of the final loop, exceeding the VNE of 240 km/h.
- The structural failure of the right wing was caused by exceeding both the maximum allowable speed and the maximum permissible load factor.