What happened
On April 27, 1967, at approximately 11:45 AM, a Piper Cherokee-Six, registration HB-OMB, departed Zurich Airport for a scheduled commercial sightseeing flight. The aircraft was carrying the pilot and five passengers. Shortly after takeoff, while the aircraft was climbing and executing a prescribed right turn, the engine power dropped rapidly.
In an attempt to maintain altitude, the pilot applied power and manipulated the throttle, but the engine could not sustain flight. The pilot subsequently performed an emergency landing in a meadow outside the airport perimeter. While the landing itself was successful, the aircraft struck the airport's perimeter fence, which was difficult to see due to its dark, oxidized condition. The impact caused heavy damage to the Piper Cherokee-Six, though all occupants escaped the wreckage without injury.
The investigation
The investigation focused on the fuel system and the sequence of events leading to the power loss. Investigators examined the fuel levels in all four tanks—two wing tanks and two main tanks—following the accident. A post-accident inspection revealed that the wing tanks were empty, while the main tanks remained nearly full.
Technical examinations of the fuel quality and the engine's mechanical condition ruled out contaminated fuel or mechanical failure of the engine or fuel delivery system. Testing on a similar aircraft model indicated that switching fuel tanks during flight can cause a temporary loss of engine power for several seconds. Additionally, investigators looked into the pilot's pre-flight checks and the accuracy of the cockpit fuel gauges.