What happened
On August 21, 2009, a Robinson R22 Beta helicopter, registration HB-XZN, was conducting a VFR training flight near Weienbrunnen, Switzerland. The flight was being conducted by a flight instructor in training, who had taken control of the aircraft to allow the student pilot a brief rest during a series of intensive maneuvers.
While performing a turn at an altitude of approximately 20 to 25 meters above the ground, the instructor attempted to execute a left-hand turn near a wooded area. During the maneuver, the aircraft's forward airspeed dropped rapidly, and the helicopter entered an unintended descent. As the pilot attempted to correct the situation by increasing collective pitch, the engine power was insufficient to maintain rotor RPM, leading to a low RPM warning. The aircraft subsequently struck the ground with its landing gear, causing significant damage to the airframe and landing gear.
Despite the impact, the pilot managed to maintain enough control to prevent the helicopter from rolling over and decided to fly the damaged aircraft back to Beromünster airfield.
The investigation
SUST examined the flight data, aircraft wreckage, and statements from both the instructor and the student. The investigation confirmed that the aircraft was within its weight and center of gravity limits and that no mechanical failures contributed to the accident. The investigation also reviewed the meteorological conditions, noting a light northwest wind and favorable visibility.
Findings
- The pilot underestimated the aerodynamic demands of performing a low-altitude turn under the prevailing wind conditions.
- The aircraft experienced a rapid loss of airspeed and an increase in bank angle to approximately 45 degrees.
- The attempt to increase collective pitch to arrest the descent caused the rotor RPM to drop below safe limits.
- The spatial constraints of the training area limited the pilot's ability to execute a safe escape maneuver once the descent began.
- The landing gear absorbed much of the impact energy, preventing a more catastrophic rollover.