What happened
On June 7, 2008, an AutoGyro MT03 Turbo with registration 31-HK departed from the Bois-de-la-Pierre airfield in France. The pilot, who was transporting the aircraft to a new owner at Luchon, was flying in a straight line at a low altitude when witnesses observed pieces of the aircraft's tail detaching and falling. Following the structural failure, the aircraft rolled onto its back and struck the ground in a field near Marignac-Lasclares with high intensity, resulting in a post-impact fire. The pilot, a 46-year-old man with extensive experience in high-performance fixed-wing aircraft but limited hours on this specific autogyro type, sustained fatal injuries.
The investigation
Investigators examined the wreckage and debris field, which stretched approximately 150 meters. The debris included sections of the horizontal and vertical stabilizers, the propeller, and the pilot's helmet visor. Technical analysis by CETIM focused on the composite tail structure to determine if manufacturing defects were present. The investigation established that the vertical stabilizer had undergone at least two successive impacts from the rotor blades. Furthermore, the presence of red paint from the tail on the rotor blades confirmed the interaction between the blades and the tail assembly. The investigation also looked into the aerodynamic phenomenon of rotor flapping and how sudden control inputs might influence the load factor.
Findings
- The primary cause of the accident was the in-flight failure of the tail assembly caused by the rotor blades striking the vertical stabilizer.
- This structural failure was triggered by rotor flapping, a phenomenon where the rotor speed decreases and the blades move vertically due to a reduction in the load factor.
- The reduction in the load factor was likely caused by sudden, large-amplitude control inputs on the pitch axis.
- It is suspected that the pilot may have made an instinctive, abrupt movement on the cyclic control following the unexpected detachment of his helmet visor during flight.
- The pilot's extensive background in aerobatic fixed-wing flight may have contributed to the accident, as the reflexive, high-intensity control techniques used in aerobatics differ significantly from the smooth, subtle inputs required for safe autogyro operation.