What happened
On February 7, 2009, a Robinson R22 Beta helicopter was conducting a training flight at Donaueschingen airfield as part of a flight instructor rating course. The flight, operated by an instructor and a student pilot, consisted of several maneuvers, including normal approaches and various types of autorotations. During the fourth of several planned short-distance autorotations, the aircraft entered a critical state.
At approximately 1,000 ft, the student pilot initiated the autorotation while flying south toward the threshold of runway 18. The pilot then executed a left turn toward the east before attempting to curve back toward the intended landing point. During these turns, the student manipulated the collective pitch lever to control the main rotor RPM, which caused the airspeed to drop to approximately 50 kt. In an attempt to regain the required autorotation speed of 60 to 70 kt, the student pushed the cyclic forward. However, while this increased airspeed, it caused the main rotor RPM to decrease.
The instructor attempted to intervene by lowering the collective pitch and increasing engine power using the throttle. Despite these efforts, the aircraft's sink rate reached approximately 1,800 ft/min, which could not be sufficiently reduced. The helicopter struck the ground in a nose-up attitude and slid approximately 40 meters before coming to rest on its left side. Both occupants escaped the wreckage without injuries.
The investigation
The BFU investigation relied on statements from the pilots, as the aircraft was not equipped with flight data recorders and the accident site had been cleared and covered by new snow by the time investigators arrived. The investigation examined the physical condition of the Robinson R22 Beta, which showed significant structural damage, including bent main rotor blades, a broken swashplate component, and a severed tail rotor drive shaft. No mechanical failure was reported by the crew.
Findings
- The primary cause of the accident was the inability to maintain a stable descent rate and airspeed during the autorotation maneuver.
- The student pilot's control inputs—specifically pulling the collective to manage RPM—led to a dangerous reduction in airspeed.
- The subsequent attempt to regain airspeed by pushing the cyclic forward resulted in a loss of main rotor RPM.
- The descent rate of 1,800 ft/min exceeded the instructor's ability to recover the aircraft before impact.
- The manufacturer's safety notice (SN-38) specifically warns of the risks during training autorotations, recommending that the maneuver be aborted if airspeed, rotor RPM, or sink rates deviate from stabilized parameters.