What happened
On 9 March 1998, a Robinson R22 Beta, registration G-BUIW, was conducting a private flight from Thruxton Airfield. The pilot, who had recently obtained his Private Pilot's Licence, had planned a local flight to practice circuit flying. After departing Thruxton, the helicopter flew towards an area northwest of Andover.
Witnesses in the villages of Amport and Monxton observed the aircraft flying normally before the engine appeared to fail, with some noting a spluttering sound. Shortly after, the helicopter was seen descending with the main rotor blades significantly bent upwards, a condition typically indicating a loss of rotor RPM. The aircraft struck a ploughed field on a hilltop, resulting in 1 fatality and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and found that the aircraft had remained upright during its vertical descent. While the engine and fuel systems were too damaged for full testing, the investigation noted that the carburettor hot air selector valve was in the cold position. The engine's cooling fan and shroud showed no signs of rotation, suggesting the engine had ceased running prior to impact.
Technical analysis of the engine revealed low compression in two cylinders. Although some issues were attributed to impact-related debris, the investigation also noted that the engine had been running with a very weak mixture. Furthermore, the magnetic chip detector in the main rotor gearbox was heavily contaminated with metallic particles. While the low rotor RPM warning light was functional, the debris on the detector might have prevented the warning light from illuminating during the flight.
Medical examinations of the pilot revealed no pre-existing diseases that would have contributed to the accident, though traces of cannabis were found in the blood and urine. The levels suggested recent ingestion, though not necessarily on the day of the flight.
Findings
- The engine suffered a loss of power, likely due to the engine failing to maintain sufficient power during the flight.
- The pilot was flying outside the standard 30-day currency requirements.
- The main rotor RPM decreased to an unrecoverable level, evidenced by the upward bending of the blades.
- Metallic debris was present in the main rotor gearbox chip detector.
- The pilot's recent ingestion of cannabis was noted, though its direct impact on flight performance was not quantified.