What happened
On April 9, 2009, a Robinson R22 Beta II helicopter, registration HB-ZGR, was conducting a VFR training flight at Bern-Belp Airport. The flight, involving a flight instructor and a student pilot, was focused on practicing emergency procedures, specifically autorotations. After completing several standard straight-in autorotations, the instructor decided to perform a specialized demonstration maneuver involving a 180-degree turn at low altitude.
During this maneuver, the instructor reduced airspeed and initiated a turn. As the aircraft attempted to regain airspeed, the rotor RPM dropped to approximately 95%, triggering the low RPM warning. The instructor realized that the remaining altitude was insufficient to complete the maneuver safely. Despite attempting to maintain a horizontal attitude and applying full collective just before impact to cushion the landing, the helicopter struck the grass runway with significant force. The impact caused the landing gear to deform and the tail rotor shaft to break. Both occupants were able to exit the wreckage via the open cockpit; the instructor sustained one minor injury, while the student was uninjured.
The investigation
The SUST investigation examined the flight logs, GPS data, and statements from both the instructor and the student. The investigation focused on the flight dynamics during the specialized maneuver and the decision-making process regarding altitude and airspeed. Investigators also reviewed the aircraft's technical condition and the pre-flight briefing, which had explicitly discussed the risks of the planned maneuver.
Findings
- The primary cause of the accident was the helicopter striking the grass runway during a failed autorotation demonstration.
- The instructor failed to plan an adequate safety altitude for the combined maneuvers, initiating the second part of the exercise at only about 300 ft AGL, well below the manufacturer's recommended decision height of 500 ft AGL.
- The instructor did not abort the demonstration despite encountering unstable flight elements and insufficient energy.
- The instructor's attention was likely divided by the effort to verbally instruct and comment on the maneuvers during the complex flight phase.
- The aircraft's weight at the time of the accident was approximately 1310 lb, within limits.