What happened
On 27 April 2003, a Robinson R22 Beta, registration G-LEDA, was conducting a private flight near Royston, Hertfordshire. The flight was intended to conclude with a landing in a client's garden at an altitude of approximately 300 to 500 feet.
As the aircraft was on its downwind leg, the pilot experienced a sudden leftward pull and heard a loud grumbling noise. Believing an engine failure had occurred, the pilot initiated an autorotation procedure, attempting to increase airspeed to 75 knots. During the subsequent turn into the wind, the pilot attempted to flare the aircraft; however, the right skid struck the ground first, causing the helicopter to roll onto its right side. The incident resulted in one injury to the pilot and one injury to the passenger.
The investigation
Investigators examined the wreckage and found that the aircraft had struck the ground with significant vertical speed. While the cabin and skid structures were compressed, evidence of rotation on the rotor blades and the drive train indicated that the engine was still operational at the moment of impact.
Upon inspection of the transmission compartment, investigators discovered that one of the two transmission 'vee' belts was missing. Rubber deposits within the compartment suggested the belt had flailed after failing, and small fragments of the belt were recovered from the site. The second belt remained intact and undamaged, and the sheave rims showed no signs of damage. The actuator was found in a mid-position. Notably, the belts had been replaced only 12 hours prior to the accident.
Findings
- The primary cause of the accident was the failure of one transmission 'vee' belt.
- The passenger had noted that the clutch warning light had been illuminating periodically for several seconds during the flight.
- The failure occurred in a relatively new belt, which is a known phenomenon in this aircraft type, often occurring within the first 50 hours of service.
- The investigation noted that new belts are softer and more prone to climbing out of the sheave grooves, which can lead to an overload condition and subsequent tearing.