What happened
On the morning of September 22, 2016, a pilot operating a Robinson R2-BETA, registration HB-ZOG, departed from Raron airfield for a flight toward the Zermatt region. The flight was conducted under visual flight rules (VFR) in clear skies with light easterly winds. After flying south toward the Mattertal valley, the pilot performed two low-level passes over the mountain landing site at Äschhorn.
During the second, lower pass at approximately 09:15 local time, the helicopter disturbed approximately 30 cm of fresh snow, creating a whiteout condition that threatened the pilot's visual reference to the ground. Attempting to abort the low pass, the pilot initiated a go-around by climbing in a descending direction. However, the aircraft was operating at its performance limits. As the pilot attempted to gain forward airspeed, the main rotor RPM began to decay, triggering the low RPM warning horn.
During the maneuver, the helicopter's skids struck a snowdrift, causing a significant deceleration. Realizing that insufficient power remained for a successful go-around, the pilot pulled back on the cyclic stick to reduce airspeed. This resulted in the tail of the Robinson R22 BETA striking the snow, causing the tail boom to break off. The aircraft then struck the ground heavily on the left skid and overturned. The impact was cushioned by the deep snow, and the pilot was able to exit the wreckage without fire. The pilot sustained light injuries.
The investigation
SUST examined the performance capabilities of the aircraft relative to the environmental conditions at the time of the accident. The investigation focused on the altitude of the landing site compared to the aircraft's operational limits.
Findings
- The landing site at Äschhorn is situated at approximately 11,600 ft AMSL.
- Based on the aircraft's weight and the atmospheric conditions (ISA +8 °C), the maximum altitude for hovering out of ground effect (HOGE) was approximately 10,500 ft AMSL.
- The landing site was approximately 1,000 ft above the aircraft's maximum HOGE capability, meaning the aircraft was operating beyond its performance limits for a stable hover or transition during the maneuver.