What happened
On the morning of May 4, 2001, a Robinson R22 Beta helicopter, registration HB-XTZ, crashed near Gossau, Switzerland. Shortly after takeoff, the aircraft experienced a sudden loss of engine power. The pilot, who was flying solo, was unable to successfully execute an autorotation maneuver. As a result, the rotor system experienced a stall and came to a complete stop before the aircraft impacted a field. The pilot sustained serious injuries, including severe head and spinal trauma.
Prior to the flight, the pilot had removed the left passenger door to facilitate aerial photography for a passenger. The aircraft had been fueled from a 200-liter drum of AVGAS stored in a local garage.
The investigation
The investigation examined the aircraft's mechanical condition, the pilot's training, and the prevailing meteorological conditions. Technical analysis of the engine performed on a test bench showed no functional defects, and the engine operated normally during testing. Investigators found that the main and tail rotors had stopped spinning before impact, evidenced by specific deformation patterns on the blades known as "coning."
Regarding maintenance, the investigation revealed that the required 25-hour inspection intervals had not been maintained. Additionally, the aircraft's Airplane Flight Manual (AFM) had not been updated with recent manufacturer revisions concerning carburetor icing precautions.
Findings
- The primary cause of the accident was the failure to maintain control during an autorotation following an engine failure.
- The engine failure was most likely caused by carburetor icing.
- Contributing factors included a failure to recognize high-risk meteorological conditions; although no visible moisture was present, there was a very narrow spread between the temperature and the dew point.
- The pilot did not utilize the carburetor heat effectively.
- The pilot's recent training in "Low RPM Recovery" and autorotation procedures was insufficient, as the last such training had occurred seven months prior to the accident.
Safety action
- The investigation noted that the aircraft was not in an airworthy state due to missed 25-hour maintenance intervals and an outdated flight manual.