What happened
On June 23, 2003, a Cessna 172 RG, registered as HB-CGR, departed from the Gruyères aerodrome for a flight to Langenthal. Shortly after takeoff from runway 17, the aircraft failed to gain sufficient altitude and struck trees on the northwest spur of the Dent de Broc at approximately 10 meters above ground level. The impact caused the aircraft to catch fire, and all four fatalities occurred as a result of the crash.
Prior to the accident, the pilot had arrived at Gruyères from Langenthal. Witnesses at the aerodrome noted that the pilot had been warned about significant crosswind gusts. During the takeoff roll, observers noted the aircraft drifting toward the left side of the runway and observed that the landing gear retraction process appeared slower than usual.
The investigation
The investigation established that the engine was operating at full power at the moment of impact, and the aircraft's weight and center of gravity were within prescribed limits. Technical analysis of the propeller blades and wreckage ruled out mechanical failure as a cause.
The investigation focused on the environmental conditions and the pilot's operational profile. At the time of the accident, the temperature was 32°C, resulting in a high density altitude of 4,750 feet. Additionally, the region was experiencing turbulent conditions caused by shifting lateral, upward, and downward winds.
Findings
- The primary cause of the accident was the aircraft's inability to climb or maneuver effectively to avoid obstacles due to the chosen flight attitude.
- The pilot possessed limited flight experience, with only 172 total hours and very little recent training. The pilot was unfamiliar with performing takeoffs from mountain aerodromes or grass runways.
- Reduced aircraft performance was caused by a combination of high density altitude, a relatively high takeoff mass, and severe turbulence from shifting winds.
- The aircraft's flight path showed a descending trajectory of approximately 19 degrees just before the collision.