History of Flight
On the evening before the accident, the pilot flew the Robinson R22 Beta (registration HB-XTZ) to Gossau, Switzerland, and stored the helicopter overnight in a garage workshop. He refueled from a 200-liter drum of AVGAS, though the precise amount was not recorded. On the morning of May 4, 2001, shortly before 07:00 local time, the pilot, with the assistance of the garage owner, prepared the helicopter for departure. The left (passenger) door was removed because the pilot intended to pick up a passenger with a camera in nearby Arnegg. No one observed the pilot taking fuel samples from the three drains before flight.
Shortly after takeoff from Gossau, heading north parallel to a highway access road, the engine power output ceased. According to witness statements, the helicopter descended from an unspecified height and crashed. The pilot was seriously injured.
Injuries and Damage
The pilot, the only person on board, sustained serious injuries. The helicopter was destroyed. There was no fire. A small amount of fuel spilled into the grass, but no third-party property damage occurred.
Meteorological Information
Conditions at the accident site around the time of the accident, as reported by the Swiss Meteorological Institute, were: clouds 3-4/8 at approximately 4800 ft MSL and 3-5/8 at 6200 ft MSL; visibility about 15 km; wind 100° at 1-3 knots; temperature +10°C, dew point +8°C; QNH 1007 hPa. The lowest temperature during the preceding night was +9°C with dew point +7°C. Weak showers were noted on a line from Winterthur to Frauenfeld, Konstanz, and Ravensburg.
Wreckage and Impact
The helicopter struck a flat meadow about 80 meters south of the highway. The impact had a slight left and rearward attitude, breaking the left rear skid. The helicopter, traveling north, overturned after impact and came to rest on its right side, facing south. There was no evidence of in-flight contact with obstacles, birds, or objects, nor any indication that rotor blades struck the cabin or tail boom. The main and tail rotors came to a stop before impact, as confirmed by multiple witnesses. All damage resulted from the impact.
Medical and Pathological Information
No evidence of foreign substances that could have negatively affected the pilot's mental or physical functions at the time of the accident was found. The pilot survived but sustained severe back and head injuries. The report notes that wearing a helmet might have prevented or reduced the head injuries.
Tests and Research
Fuel samples from the crash site corresponded to commercial AVGAS 100 LL. Examination of the main rotor blades showed no signs of rotation during ground contact; coning marks were present, indicating reduced rotor rpm. The tail rotor blades were found separated, with fracture characteristics consistent with a stationary rotor. The engine-driven cooling fan showed no evidence of rotating contact with the cowling. The tail rotor shaft, pulleys, and Thomas couplings displayed no marks from rotation. The engine was removed and tested on a test stand, where it performed perfectly; carburetion, compression, ignition, and power were normal. No direct link between engine condition and the accident was found.
The helicopter's flight manual had not been updated to include a mandatory revision (HB1998-262) issued by the Federal Office for Civil Aviation, which contained operational changes related to carburetor icing. The owner had not incorporated this revision.
Organizational and Procedural Information
The pilot had chartered the helicopter from Airport Helicopter Basel and flown it from Zurich-Kloten to Gossau the day before. He had previously conducted private sightseeing flights in the Gossau/St. Gallen area, storing the helicopter overnight in a garage. Fuel for these flights came from the same 200-liter drum of AVGAS. The R22 flight manual contains safety notices, including SN-25 on carburetor ice, which covers symptoms, prevention techniques, and proper use of carburetor heat.
Probable Cause
The accident resulted from the pilot's failure to maintain control during autorotation after an engine failure. The engine failure was most likely caused by carburetor icing. Contributing factors were: lack of awareness of weather conditions (no visible moisture but a very small temperature-dew point spread), improper use of carburetor heat, and insufficient recent training in low rpm recovery and autorotations.