What happened
On the afternoon of December 13, 1973, a Cessna 150 (registration HB-CTO) departed Ecuvillens for Lausanne. The flight was intended to be a routine trip, with the pilot flying alongside an experienced instructor in a second aircraft. During the flight, the weather conditions rapidly deteriorated due to an approaching low-pressure system, bringing low cloud ceilings, heavy mist, and icing.
As the flight progressed, the pilot's visibility dropped significantly. Radio transmissions from the aircraft tracked a path through various locations, including Orbe, Echallens, and Moudon. By 16:35, the pilot reported being near Cheyres at 3,700 feet. However, shortly after announcing a heading of 300 degrees, the pilot stated that visibility had been lost entirely. The aircraft failed to respond to further radio calls from Ecuvillens, and the flight disappeared into the night.
Following the disappearance, extensive search operations involving helicopters from the Swiss Air Force and civilian organizations were conducted. While the main wreckage was never recovered, the nose wheel and the right main landing gear of the HB-CTO were discovered washed up on the shore at Cudrefin approximately ten days later.
The investigation
Investigators examined the flight's progression, the meteorological data, and the pilot's last known communications. The investigation established that the aircraft was well-maintained, with valid certificates and a weight and balance within prescribed limits. The pilot held a valid private pilot license and showed no signs of impairment or distress in his final radio transmissions.
Analysis of the pilot's radio positions revealed a significant navigational error. While the pilot's reported locations initially followed a logical route, his later descriptions—such as being near a lake along mountains—did not align with the actual geography of the intended path, suggesting he had become disoriented.
Findings
- The primary contributing factors were the worsening meteorological conditions, specifically the low cloud ceiling and heavy mist, combined with the onset of darkness.
- The pilot experienced a total loss of orientation during the flight.
- The flight preparation was deemed insufficient for the deteriorating weather conditions encountered.