What happened
On April 17, 1977, a private VFR flight involving a Cessna 150 L, registration HB-CDX, experienced a complete engine failure while maneuvering near Lausanne, Switzerland. After a flight from Lausanne to Gruyères and back, the pilot was executing a right-hand turn to join the airfield circuit at 3,500 feet when the engine began to misfire, followed by a total loss of power three seconds later.
Recognizing the danger of attempting to reach the airfield due to numerous obstacles along the route, the pilot opted for an emergency landing in a nearby field at Manloud. During the approach, the aircraft encountered overhead power lines and a telephone line. While attempting to avoid houses in the final approach, the aircraft's right wing struck an electrical line. The aircraft struck the ground on its left wing and nose gear, eventually flipping onto its back. The two occupants sustained minor injuries, but the aircraft was destroyed.
The investigation
The investigation focused on the engine failure and the subsequent impact with ground obstacles. Investigators examined the fuel levels, noting that the pilot had checked the gauges prior to departure and found the tanks to be mostly full. At the time of the accident, the aircraft had been flying for four hours since its last refueling. Post-accident analysis of the fuel remaining in the tanks indicated an average consumption rate of approximately 22 liters per hour.
Findings
- The primary cause of the accident was a fuel exhaustion resulting from an unsuccessful forced landing in an area with high obstacle density.
- The fuel gauges on the aircraft provided imprecise readings, which led to an inaccurate assessment of the remaining fuel.
- The pilot's pre-flight preparation was insufficient, as the actual fuel remaining was lower than anticipated due to the duration of the flight since the last refueling.
- The presence of telephone and electrical lines, which were difficult to see in the late afternoon light, contributed to the loss of control during the final approach.