What happened
On October 9, 1970, a Piper J3C, registration HB-OUO, was conducting a training flight near Bad Ragaz when the engine experienced a sudden failure shortly after takeoff. The flight, which included a flight instructor and a student pilot, had just completed a circuit of the airfield. Following the takeoff, the student pilot reduced power to reach the required climb RPM, at which point the engine RPM dropped significantly and failed to recover despite the instructor's attempts to increase throttle.
Due to the low altitude and the presence of obstacles—including a row of poplar trees and high-voltage power lines directly in the flight path—the instructor initiated an emergency maneuver to the right toward an adjacent meadow. During this attempt to avoid the power lines, the aircraft's right wing strut struck a tree canopy, causing the plane to yaw sharply to the right. The aircraft subsequently struck the ground with significant force.
The investigation
The investigation examined the aircraft's mechanical condition, the weather, and the pilot's actions. Investigators found that the engine's fuel system and ignition components were functional up to the carburetor. While carburetor icing was considered a possibility, the rapid nature of the power loss and the lack of symptoms during previous flight segments made this unlikely.
Crucially, the investigation noted that the aircraft's fuel tanks lacked drain valves, which prevented the pilot from checking for water contamination during pre-flight inspections. The investigation also noted that the aircraft was slightly overweight at the time of the accident.
Findings
- The primary cause of the accident was a failed emergency landing in difficult terrain following an engine failure.
- The engine failure was most likely caused by water contamination in the fuel.
- The presence of water in the fuel could not be ruled out as a result of refueling at the airfield, as the lack of fuel tank drains prevented a pre-flight check for water.
- The aircraft's right wing strut struck a tree during the maneuver to avoid power lines, leading to the final impact.
Safety action
No specific safety recommendations were recorded in the final report.