What happened
On July 2, 1973, a Piper PA28-180, registration HB-OLK, departed from Birrfeld airfield for a private VFR sightseeing flight. The flight was intended to travel over Lake Constance to Rapperswil and back. The aircraft was carrying the pilot and three passengers.
During the flight near Stein am Rhein, several witnesses observed the aircraft performing unusual maneuvers. Some observers noted changes in engine noise, while others described the aircraft performing steep dives and climbs. One witness reported seeing the aircraft enter a steep dive, followed by an abrupt transition into a climb at an angle of approximately 45 degrees. As the aircraft climbed, it appeared to lose speed significantly, eventually reaching a near-stall condition before banking sharply and entering a descent into the wooded terrain of the Öhninger Büel.
Upon impact with a 35-degree slope, the aircraft was destroyed. All four fatalities occurred at the scene.
The investigation
An investigation was conducted by the Swiss Transportation Safety Investigation Board in conjunction with the Schaffhausen Cantonal Police. Investigators examined the wreckage and the flight history of the aircraft. The engine was disassembled, and while some evidence of overheating on the exhaust valve petals was found, no pre-existing technical failures were identified that could explain a total engine failure. The aircraft's weight and center of gravity were found to be within permissible limits.
Witness accounts were analyzed to understand the aircraft's final moments. While some witnesses believed the maneuvers might have been intentional aerobatics, others noted the engine noise fluctuated. Investigators also considered whether the unusual flight path was caused by the pilot's maneuvers, or if a passenger had interfered with the dual controls.
Findings
- The aircraft was airworthy and properly registered.
- The pilot held a valid private pilot license and was medically fit.
- Meteorological conditions were favorable, with clear summer weather and no significant weather-related hazards.
- The pilot's blood alcohol level was within legal limits and not a contributing factor.
- The aircraft fell below its minimum flying speed during a steep climb, and the remaining altitude was insufficient to recover the flight path.