What happened
On April 26, 1972, a pilot operating a Cessna 150, registration HB-CTD, departed from La Côte airfield for a solo VFR flight. After traversing Lake Geneva and flying along the French coast toward Bex, the pilot turned toward Montreux with the intention of overflying a specific building in Caux at an altitude of approximately 1,150 meters.
As the aircraft began its ascent from 200 meters above ground level, the pilot attempted a wide right turn to clear a ridge northeast of Caux. During this maneuver, the aircraft's airspeed dropped from an initial 60 mph to between 40 and 50 mph. Fearing a stall, the pilot opted to continue a direct climb rather than executing a corrective turn. During the ascent, the right wingtip struck a tree branch at an altitude of approximately 5 to 6 meters. Despite the impact, the pilot maintained control and successfully returned the aircraft to the departure airfield.
The investigation
The investigation focused on the aircraft's performance and the pilot's flight path. The Cessna 150 was found to be in airworthy condition, with the weight and center of gravity remaining within prescribed limits. No mechanical failures were identified as contributing factors. The investigation also reviewed the pilot's credentials, noting a private pilot license with radio extensions and approximately 300 total flight hours, including 14 hours on this specific type.
Investigators reconstructed the flight path and determined that the aircraft's climb performance was marginal for the intended trajectory. Meteorological conditions on the day of the event included a moderate north wind (bise), which frequently generates turbulence near the local terrain.
Findings
- The aircraft's climb performance was insufficient for the chosen flight path through the mountainous terrain.
- The pilot's attempt to increase the climb angle by pulling back on the elevator likely increased the angle of attack, which may have led to a miscalculation of the actual climb gradient.
- The reduction in airspeed during the turn indicated that the aircraft was operating at the edge of its performance capabilities.
- The flight path between Montreux and Caux lacked an adequate safety margin for mountain flying.