History of the Flight
The pilot collected the helicopter from Thruxton Aerodrome the day before the accident, where it had undergone an annual maintenance check. The helicopter needed three to four hours of flight before a torque check on the main rotor mast assembly. The pilot flew it uneventfully from Thruxton to a private site near Peldon, Essex, a flight of 56 minutes. The helicopter was parked overnight and refuelled.
On the day of the accident, the pilot intended to fly to Wellesbourne Mountford Aerodrome to meet a passenger for a sightseeing trip, then return to Thruxton. The weather was clear, temperature about 28°C, with a light easterly breeze. A photograph taken before the first flight showed no visible oil leak.
Before departure, the pilot completed a walk-around, including checking fluid levels; the engine oil sight glass showed full. The flight from Peldon to Wellesbourne (55 minutes) was uneventful. Before the second flight, the pilot again checked the oil sight glass, which still showed full. Fuel onboard was 620 lbs.
Accident Sequence
The pilot and passenger departed Wellesbourne at 1039 hrs. Two witnesses observed the helicopter in flight. One witness, south of Bidford-on-Avon, saw a "contrail" from above the cabin but below the rotor. Another witness near Dorsington saw "white smoke," heard a "popping noise," saw the smoke turn grey, and the helicopter descend near Long Marston.
In the cockpit, the first indication was an amber FADEC fault light. The pilot noted NR at 100% and NP at 90%. Concerned by reduced power, he briefly switched to manual FADEC mode and confirmed engine response, then returned to automatic. A few seconds later, an amber FADEC degraded light illuminated. About 27 seconds later, a "mechanical snapping noise" occurred, a violent left yaw, the red engine out warning illuminated, torque dropped to 3%, and a horn sounded. The pilot lowered the collective, slowed to 60 kt, established autorotation, selected a field, and made a MAYDAY call.
During the autorotation, the pilot focused on NR, airspeed, and the field. He flared and raised collective, touching down then skipping a few feet. Both occupants exited through their doors. The pilot saw an "off white coloured" liquid on the windscreen. Flames appeared below the rotor. Photos taken by the pilot show the helicopter burning; neither occupant was injured.
Accident Site and Damage
The helicopter landed upright in a crop field with no evidence of sliding. The tail boom separated and lay in four sections to the right, covered in oil and not fire-damaged. The main wreckage was destroyed by fire. One main rotor blade had witness marks consistent with striking the tail boom.
Investigation Findings
The engine suffered an uncontained failure of the gas producing turbine disc due to insufficient oil reaching the bearings as a result of an oil leak. Due to extensive damage, the cause of the oil leak could not be determined.
Two Safety Recommendations were made regarding the Failure Mode and Effects Analysis for the engine, and the fire resistance and crashworthiness of aircraft components. The helicopter manufacturer undertook two Safety Actions regarding advice to pilots and one Safety Action regarding analysis of the airframe fuel filter.