What happened
On September 20, 1970, a Cessna F-150 J, registration HB-CUO, departed Agno for a local flight. While flying over Lake Locarno near the Maggia delta, the pilot observed the fuel gauges drop to zero. Believing the aircraft was running out of fuel, the pilot decided to perform an emergency landing at the nearby Ascona airport. During the approach, the pilot also reported irregular engine performance. After two unsuccessful landing attempts, the pilot initiated a third approach. During a left-hand descending turn, the aircraft entered a steep dive and struck the right edge of the runway, approximately 400 meters from the threshold. The impact caused damage to the engine compartment, nose gear, and propeller. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's electrical and mechanical systems following the incident. While the engine and fuel filters were found to be functioning normally, an expert noted that the right magneto was improperly calibrated and required replacement. The investigation focused on why the fuel indicators showed zero despite fuel being present in the tanks. It was determined that the aircraft's electrical master switch or specific circuit valves could be accidentally toggled due to their cockpit placement. Furthermore, the investigation reviewed the pilot's training, noting that while the pilot held a valid license, they lacked comprehensive knowledge of the specific systems and emergency procedures for the Cessna F-150 J.
Findings
- The primary cause of the accident was an early stall during a turning approach.
- The pilot's high level of stress, following the perceived fuel loss, likely contributed to two missed approaches and a lack of proper configuration on the final attempt.
- On the third approach, the pilot performed a left turn with the flaps retracted and the engine at low power, significantly increasing the stall speed.
- The pilot's lack of familiarity with the aircraft's electrical switch layout likely led to the accidental interruption of the fuel gauge circuit.
- The perceived engine malfunction was likely a subjective sensation caused by the high-stress environment rather than a mechanical failure.