What happened
On the evening of 30 August 2001, a Hughes 369E helicopter, registration SE-HN and HNZ, was conducting a private training flight near Klimpfjäll, Sweden. After completing his scheduled flight duties for the day, the pilot initiated a series of emergency training exercises. The flight sequence involved an initial autorotation with power application, followed by a second attempt at a complete autorotation intended to end with a landing on a nearby bog area.
During the second maneuver, the pilot descended to approximately 150 feet. At this altitude, the pilot noted that the airspeed was relatively high, at roughly 70 knots. In response, the pilot began the recovery process earlier and at a steeper angle than in the previous exercise. As the aircraft reached the ground, the contact was heavy and accompanied by forward momentum. Immediately following the touchdown on the soft, wet terrain, the pilot observed an object flying past the cockpit and felt a distinct imbalance in the rotor system. Upon inspecting the aircraft, it was discovered that the main rotor blades had struck the tail boom, severing a section of it.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the flight history and the mechanical state of the aircraft. The investigation established that the pilot had been on duty for over ten hours prior to the accident, having completed 30 takeoffs and landings during his commercial duties. The investigation focused on the execution of the autorotation maneuver and the physical interaction between the rotor blades and the tail boom during the hard landing.
Findings
- The primary cause of the accident was a miscalculation during the recovery phase of the autorotation, which led to the main rotor RPM being too low at the moment of touchdown.
- The resulting hard impact caused the main rotor blades to flex downward with enough force to sever the tail boom.
- The pilot's fatigue, resulting from a long workday, may have contributed to the error in judgment during the maneuver.