What happened
On July 21, 2021, at approximately 11:48 AM, an AutoGyro MTOsport gyrocopter was performing circuit training at Hildesheim airfield. The flight, which was part of a student pilot's training, involved a flight instructor and a student. After completing 11 successful circuits, the aircraft was transitioning from the crosswind leg to the final approach for runway 25 when a rotor blade suddenly detached from the rotor head.
The structural failure caused the aircraft to disintegrable in mid-air. The instructor was thrown from the wreckage, and the aircraft struck the ground near the airfield perimeter. The accident resulted in 2 fatalities (the pilot and the student) and the destruction of the aircraft. The impact also caused damage to nearby property.
The investigation
The BFU investigation focused on the rotor blade design, maintenance records, and the airworthiness inspection process. Investigators examined the wreckage and found that the rotor blade had detached at the outermost attachment bolt. Metallurgical analysis conducted by the Technical University of Braunschweig revealed that the failure was a fatigue fracture.
Key findings during the physical examination of the rotor head included significant corrosion on the blade attachment bolts, the rotor hub bolts, and the mast bolts. No traces of lubrication were found on these components. Furthermore, the investigation revealed that the aircraft's total operating time was approximately 3,940 hours, significantly higher than the 1,250 hours indicated by the cockpit hour meter, which had been replaced in 2017 without proper documentation of the total accumulated time.
Findings
- The primary cause of the accident was the detachment of a rotor blade due to a fatigue fracture.
- The rotor blade had exceeded its recommended service life, having been operated for approximately 1.6 times the manufacturer's recommended duration.
- There was a critical failure in maintenance oversight; essential periodic inspections for cracks in the blades and corrosion on the hub bolts were not documented or performed.
- The aircraft was being operated above its maximum allowable takeoff mass due to the combined weight of the occupants and the aircraft's empty weight.
- Inaccurate tracking of the total airframe hours led to a false sense of the component's remaining life and wear level.