What happened
On 1 August 2018, a Robinson R2/2 Beta, registration G-OODX, was conducting a private flight from Culworth to Worcester. While cruising at 800 ft, the pilot experienced a sudden loud bang, followed by a sharp left yaw and the activation of the low RPM horn and clutch warning light. The engine-to-rotor drive was lost.
The pilot successfully transitioned the aircraft into autorotation. To reach a suitable landing site, the pilot reduced airspeed from 60 kt to 30 kt. During the descent, the pilot disconnected the clutch circuit breaker due to the persistent warning light. As the helicopter approached the ground, the pilot attempted a flare; however, the descent rate was not sufficiently arrested, causing the tail to strike the ground before the skids made contact. The aircraft rotated forward several times before coming to a halt. The one passenger sustained minor injuries, while the pilot was uninjured.
The investigation
The AAIB investigation focused on the mechanical failure of the drive system. Although the drive belts were initially missing from the wreckage, investigators later recovered fragments of one belt from the crash site and a complete, fractured belt from a nearby field.
Laboratory analysis of the recovered belt showed no signs of degradation or misalignment, suggesting the failure was due to tensile overload. Fragments of the second belt found at the wreckage showed significant erosion, indicating it had been running improperly, likely because the automatic tensioner was exerting the full required force on only a single belt after the first had failed. The investigation could not determine the specific reason why the belts began operating incorrectly.
Findings
- The engine-to-rotor drive belts failed, resulting in a loss of power to the main rotor.
- The failure of the first belt likely caused the remaining belt to bear double the intended load, leading to its subsequent failure via tensile overload.
- The cause of the initial belt malfunction remained undetermined.
- The pilot's flare during the autorotation was insufficient to prevent the tail from striking the ground.