What happened
On February 18, 2012, a Safari helicopter was conducting flight testing maneuvers at the Lahr Airfield. The pilot had been performing hovering exercises and had completed one circuit involving an autorotation landing in a nearby field. During a subsequent takeoff, while climbing at an altitude of approximately 40 to 50 meters, the aircraft suddenly began to rotate around its vertical axis. The nose of the helicopter dipped, and the aircraft struck the runway, immediately catching fire.
Witnesses observed the aircraft at an altitude of roughly 20 to 30 meters before a component appeared to fall away, triggering the rapid rotation and subsequent crash. The impact caused significant damage to the airframe, including the destruction of the tail boom and the loss of a tail rotor blade. The pilot, a 61-year-old experienced helicopter pilot, sustained fatal injuries.
The investigation
The BFU investigation focused on the structural integrity of the tail rotor assembly. Examination of the wreckage revealed that the tail rotor spindle had fractured. Metallurgical analysis conducted by the Institute of Materials Science at the Technical University of Braunschweig confirmed that the failure was a fatigue fracture. The fracture occurred at the outer radius of the tail rotor blade bearing, a location where a structural stiffness change coincided with maximum operational bending moments.
Furthermore, the investigation found that the microstructure of the spindle's base material was unfavorable for fatigue resistance. While the tail rotor had been dynamically balanced prior to the flight, the manufacturer's analysis of the weights used suggested that the rotor assembly may have had inherent manufacturing imbalances that required significant correction.
Findings
- The primary cause of the accident was the failure of the tail rotor spindle, which led to the loss of a tail rotor blade and subsequent loss of directional control.
- The fatigue fracture was facilitated by an unfavorable material microstructure in the spindle.
- The aircraft was operating under a temporary permit for flight testing as a single-unit experimental aircraft.
- The pilot's flight experience on this specific model was relatively low, though he was a licensed helicopter pilot.