What happened
On May 1, 1971, an Agusta Bell 204 B helicopter, registration HB-XCQ, was conducting training maneuvers near Domat-Ems, Switzerland. The flight was organized by Heliswiss to allow a newly joined trainee pilot to practice full autorotative landings.
After successfully completing four landings under normal conditions, the crew attempted a fifth exercise. While descending to 1,000 feet, the pilot established a 60-knot approach speed. As the aircraft neared the ground, the trainee pilot applied a flare by pulling back on the cyclic control to reduce forward speed. During this maneuver, the rear of the helicopter struck the ground with significant force. The impact caused the aircraft to lose its tail rotor and damaged the transmission mechanism, though the crew managed to maintain control until the aircraft came to a halt on its skids.
The investigation
Investigators examined the flight crew's qualifications, the aircraft's maintenance history, and the environmental conditions at the time of the accident. The investigation confirmed that both pilots held valid licenses and that the aircraft possessed all necessary airworthiness certificates. Maintenance records showed the engine and airframe were within their service intervals, and no mechanical deficiencies were found in the aircraft's systems. Weather conditions were found to be favorable, with good visibility and light winds.
Findings
- The primary cause of the accident was a pilot error in the timing and execution of the flare maneuver during the autorotation.
- The pilot either delayed the reduction of forward speed for too long or executed an excessively aggressive flare.
- The resulting high pitch attitude caused the tail of the helicopter to strike the terrain before the aircraft could be leveled.
- The impact resulted in the destruction of the tail rotor and damage to the fuselage and transmission, though there were no injuries to the crew.