What happened
On January 29, 1999, a McDonnell Douglas MD 520N helicopter, registration HB-XGQ, departed from Schindellegi at approximately 16:30 for an avalanche prevention mission in the Hoch-Ybrig ski area. The pilot was accompanied by three piste patrollers carrying approximately 68 kg of explosive charges. After picking up the crew at the mountain station around 16:50, the aircraft proceeded toward the slopes.
While flying at a low altitude to prepare for the controlled release of explosives, the helicopter struck steep, heavily snow-covered terrain in a couloir near the Weglosen slope. The impact occurred at approximately 17:05. All four occupants—the pilot and three passengers—sustained fatal injuries. The aircraft was destroyed in the collision.
The investigation
The investigation, conducted by the Swiss Transportation Safety Investigation Board (SUST) in collaboration with various authorities, examined the wreckage and the flight conditions. Investigators located the wreckage the following morning. Technical examinations of the engine and the rotor components, performed in conjunction with the manufacturer, found no evidence of mechanical failure prior to impact. The engine was confirmed to be operational at the time of the crash.
Medical examinations of the deceased revealed that the injuries were consistent with a sudden, high-impact force, suggesting the occupants had no opportunity to take protective measures. Furthermore, toxicology reports confirmed that the pilot was not under the influence of alcohol or drugs, and all required rest periods had been respected.
Findings
- The aircraft was properly maintained and airworthy.
- The pilot was fully qualified, experienced, and medically fit for the mission.
- The crew and passengers were properly trained for the specific task of avalanche prevention.
- The primary cause of the accident was the loss of visual reference to the terrain due to diffuse lighting conditions and low-altitude flight over deep snow.