What happened
On August 22, 1994, a Robin DR 400-140B, registered HB-KDI and operated by the Motorfluggruppe Thurgau, was conducting a private visual flight from Lommis, Switzerland, to Innsbruck, Austria. The aircraft carried one pilot and three passengers. After landing in Innsbruck, the pilot prepared for the return journey, seeking detailed weather advice with a specific focus on the Stubai and Ötztal regions, where he had previously skied.
The aircraft departed Innsbruck at 12:38 UTC, flying over the Meldepunkt Sierra 2. Witnesses observed the aircraft maneuvering in the Gschnitztal valley at low altitude near steep terrain, performing sharp turns with significant bank angles. The flight path then led over the Lisenser Ferner glacier. At an altitude of approximately 10,000 feet, the aircraft entered a stall condition and slipped over its right wing. Due to the low altitude above the ground, recovery was impossible. The aircraft crashed vertically into a glacier crevasse at roughly 9,600 feet. All four occupants died instantly, and the aircraft suffered total damage.
The investigation
The Austrian Federal Ministry for Public Economy and Traffic led the inquiry, assisted by technical experts and Tirol police. The wreckage was recovered from the crevasse due to impending bad weather. A technical examination revealed no evidence of mechanical failure or pre-impact fire. The engine cylinders showed corrosion on one spark plug and water intrusion in another, but valves were free-moving. The propeller had minor bends likely caused by recovery efforts. The aircraft's weight and balance were within limits at departure.
The pilot was a 39-year-old Swiss citizen holding a valid Private Pilot License (PPL) issued in 1993. While he held a total flight experience of roughly 2,946 hours since his first license in 1974, his recent activity was minimal, with only about 13 hours logged in the three months prior to the accident. The aircraft had approximately 625 flight hours.
Findings
The investigation determined that the primary cause of the accident was the pilot's failure to maintain minimum flying speed, resulting in a stall and loss of control. This error was exacerbated by several factors:
- High Density Altitude: The aircraft operated at high gross weight (near maximum takeoff weight) in high altitude (approx. 10,000 ft) and high temperature conditions, creating a density altitude of approximately 11,800 feet. This significantly degraded performance.
- Low Altitude Maneuvering: The aircraft was flying at low altitude near steep terrain before entering the glacier area, leaving no margin for error during recovery.
- Environmental Conditions: Light downdrafts associated with the northwesterly weather pattern and glacier winds likely contributed to the stall.
- Pilot Experience: Although licensed, the pilot had very low recent flight experience (approx. 15 hours per year average), which may have impacted his ability to manage high-performance flight regimes in challenging conditions.
Safety action
No specific safety recommendations were issued by the investigation commission for this accident.