What happened
On July 1, 2019, a Robinson R22 helicopter, registration HB-XZN, was conducting a training flight near Kaltbach, Switzerland. The flight, which was part of a student pilot's training for a Private Pilot Licence (PPL(H)), involved practicing autorotations. Before the maneuver, the crew had performed a reconnaissance flight over the intended landing area to check for obstacles.
During the training session, the student pilot performed an autorotation into a field southwest of Kaltbach. As the aircraft approached the ground, the instructor initiated a go-around at an altitude of approximately 3 to 5 meters. During this maneuver, the helicopter struck a thin wire. The crew initially suspected a bird strike, but the instructor immediately took control of the aircraft and performed an emergency landing in a nearby field, shutting down the engine.
The investigation
The investigation established that the aircraft had collided with a thin, low-diameter wire, similar to those used for livestock fencing, which was stretched across the field at a height of roughly 4 meters. This type of wire is often used to allow agricultural machinery to pass under it while maintaining field boundaries. The investigation confirmed that the aircraft sustained scratches to the main rotor mast cover, the control rods, and both sides of the windscreen. There were no fatalities, though the student pilot sustained minor scratches.
Findings
- The primary cause of the incident was the collision with a low-altitude wire that was difficult to detect.
- The wire was positioned at approximately 4 meters above the ground, making it nearly invisible during the initial reconnaissance flight.
- Weather conditions were favorable, with good visibility and calm winds at 25°C.
- The use of thin wires to allow agricultural access to fields is a common practice but presents a significant hazard for low-altitude operations.