What happened
On August 12, 1969, a Cessna 150 H, registration HB-CTG, departed Zurich-Kloten at 16:45 for a flight to Agno-Lugano. Despite receiving meteorological warnings at Zurich regarding deteriorating conditions and the high likelihood of cloud cover obstructing Alpine passes, the two pilots proceeded with the flight under Visual Flight Rules (VFR).
The flight path initially headed toward the Gotthard region, but the crew was forced to turn back near Amsteg due to worsening weather. The aircraft's progress became difficult to track after leaving Erstfeld, eventually being sighted near Sedrun. Seeking a way through the mountains, the pilots navigated toward the Oberalp Pass, which was already partially closed by clouds. After crossing the pass, the crew likely spotted a slight break in the clouds near the Witenwasser Valley and entered the area near Realp.
While attempting two tight left-hand turns within the valley, the aircraft lost airspeed and stalled. The Cessna 150 H struck a slope nearly vertically at approximately 19:00, slid onto a road, and was destroyed by a post-impact fire.
The investigation
The investigation examined the flight's progression, the meteorological conditions, and the pilots' decision-making. Investigators reviewed weather reports from Zurich and various Alpine stations, which confirmed that significant cloud cover and low ceilings were present across the Gotthard, Furka, and Simplon passes. The investigation also analyzed the aircraft's technical state, finding the Cessna 150 H to be airworthy and the fuel reserves sufficient for the flight duration. Post-impact analysis of the wreckage showed the aircraft hit the terrain at a steep angle, and medical examinations confirmed that neither pilot was under the influence of alcohol or carbon monoxide.
Findings
- The primary cause of the accident was the decision by the pilots to attempt an Alpine crossing under weather conditions that were entirely inadequate for VFR flight.
- The crew employed a flight tactic that led to the accident, specifically attempting tight maneuvers in a valley while struggling with low visibility and altitude constraints.
- The pilots failed to maintain a flight path that allowed for a safe return, as they proceeded toward the Oberalp Pass despite the high risk of being trapped by closing weather.
- The aircraft experienced a loss of airspeed during low-altitude turns, leading to the fatal stall.