Swiss Investigation of Robinson R44 II Accident at Giirebad (HB-ZJG)

Incident Overview and Aircraft Details On 25 August 2010, a Robinson R44 II helicopter, registered as HB-ZJG, was involved in an accident near Giirebad, Pfyn, in the canton of Thurgau, Switzerland. The aircraft was owned and operated by Swiss Jet AG, based at Zurich Airport. The flight was a visual flight rules (VFR) training exercise involving a flight instructor and a student pilot. The helicopter was a four-seat, conventional design equipped with a semi-rigid two-blade main rotor system. ## Flight Sequence and Emergency Situation The flight began at approximately 15:55 local time from the Swiss Jet AG base. The crew conducted radio navigation procedures and confined area approaches before practicing autorotations in a forest clearing. During a planned autorotation from a height of more than 500 feet above ground level, the instructor closed the throttle. The student pilot initiated the autorotation, but the instructor observed that the manifold pressure remained at approximately 29 inches, the oil pressure was zero, and the oil pressure warning light was illuminated. The instructor took control of the aircraft at approximately 1,000 feet above ground level. ## Accident Mechanism and Damage During the flare phase of the autorotation, the instructor attempted to store energy in the main rotor. The helicopter made initial ground contact with the rear of the landing skids, which caused a forward pitch moment. The instructor reacted by pulling the cyclic stick backward. As the helicopter decelerated, a main rotor blade struck the tail boom, causing severe damage to the tail assembly. The crew did not notice the damage until after they had exited the aircraft. The helicopter was classified as substantially damaged, and there was no third-party damage. ## Personnel and Contributing Factors Both the flight instructor and the student pilot were unharmed. The instructor, a Swiss citizen born in 1981, held a commercial pilot license for helicopters and had 778 hours of helicopter experience. The student pilot, a Swiss citizen born in 1982, had 108 hours of helicopter experience. The investigation concluded that the accident was caused by inappropriate control inputs during the final phase of the autorotation, which led to the main rotor blade colliding with the tail boom. The loss of engine power during the exercise, resulting from a technical problem in the injection block, was a primary contributing factor. The instructor's experience with fixed-wing aircraft may have also contributed to the inappropriate control behavior.