What happened
On July 27, 2018, a DR 40 and/180 aircraft, registration HB-KEE, crashed into the north slope of the Col Durand ridge in the Val d'Anniviers, Switzerland. The flight, operated by Aéro-Club du Valais, was a private VFR mission intended to show passengers the Matterhorn region. After successfully completing a first flight earlier that day, the pilot departed Sion for a second leg carrying three passengers.
During the flight, the pilot attempted to gain altitude by performing several large orbits over the landscape. While navigating the area near the Glacier Durand, the aircraft was flying at a high density altitude due to warm temperatures. While executing a right-hand turn toward the Col Durand, the aircraft struck a rocky slope at approximately 72 knots. The impact destroyed the cockpit, and all four occupants were killed.
The investigation
Investigators examined Flarm electronic records, passenger testimony, and photographic evidence to reconstruct the final moments of the flight. The investigation focused on the aircraft's performance capabilities under specific environmental conditions. The DR 400/180 was operating at a high mass of approximately 1050 kg, near its maximum allowable limit.
Technical analysis of the wreckage showed that the engine was providing high power at the moment of impact. The investigation also reviewed the pilot's experience, noting an average annual flight time of only 7.5 hours over the previous decade. Environmental data confirmed that while the weather was sunny, the high temperature (ISA +15 °C) significantly increased the density altitude, which reduced the aircraft's climb performance.
Findings
- The primary cause of the accident was a high-risk mountain flight tactic that led to a collision with terrain.
- The pilot's low level of flight training contributed to the accident, particularly when managing an aircraft at its performance limits.
- The high aircraft mass and high density altitude significantly degraded the aircraft's ability to climb.
- The pilot attempted to clear the Col Durand with very little vertical margin and insufficient airspeed.
- The decision to attempt the pass without sufficient altitude reserves placed the aircraft in a precarious position during the final turn.