What happened
On 12 August 2000, a Robinson R22 Beta, registration G-BYHD, was conducting a private flight near Callander, Scotland. After approximately 15 minutes of flight from a private landing site, the pilot noticed the low rotor RPM warning horn activating and observed a decrease in rotor speed while approaching the landing area.
At an altitude of roughly 500 feet, the pilot initiated an autorotation and identified a nearby field for an emergency landing. During the final stages of the maneuver, the pilot performed a flare that was tight, resulting in minimal reduction of forward airspeed. The aircraft struck the ground heavily, causing the tail to make contact with the earth and the helicopter to bounce forward. This movement caused the aircraft to rotate to the right, eventually settling on its left skid while remaining upright. There were no injuries to the pilot or the passenger.
The investigation
The investigation examined the mechanical state of the aircraft and the environmental conditions at the time of the accident. The pilot suggested that carburettor icing was the likely cause of the rotor RPM decay. Meteorological conditions were reported as calm with 20 km visibility, an overcast ceiling of 1,500 feet, and an air temperature of 18°C, though the pilot noted the air was "very moist."
Technical inspections by a repair agency found no mechanical unserviceabilities that would have directly caused the loss of rotor RPM. The pilot noted that the engine appeared to be functioning normally following the landing. However, the pilot could not definitively confirm when carburettor heat had been applied, despite acknowledging the requirement to use it before descending.