What happened
On 13 January 2007, a Robinson R2ly R22 Beta, registration G-UNYT, was performing a private flight near Tupton, Derbyshire. The flight concluded with an approach to a private landing site at Hollis Farm. The pilot intended to transition into a hover over an adjacent field before turning east to land in the farmyard.
During the maneuver, the helicopter entered a hover and began turning toward the landing site. During this turn, the pilot reported hearing the low rotor rpm horn and seeing the associated warning light. As the aircraft descended, the left skid slid approximately 2 feet before digging into a hole in the ground. This caused the helicopter to nose over into an inverted position. Both the pilot and the passenger were uninjured and were able to exit the aircraft easily. The pilot subsequently re-entered the cockpit to shut down the engine ignition and battery master switch.
The investigation
The AAIB investigation included an examination of the wreckage and a review of the pilot's report. The investigation focused on the cause of the low rotor rpm warning and the physical cause of the nose-over.
Inspectors examined the engine governor system in the presence of a manufacturer's representative. The investigation checked the throttle connection, the friction levels of the governor and throttle linkage, and the electrical signal from the right magneto. Additionally, the engine was inspected for evidence of power at the moment of impact. The investigation also considered the aircraft's weight and balance, noting that the total weight of 595 kg was close to the maximum permitted gross weight of 622 kg.
Findings
- The left skid dug into a hole in the ground, which caused the aircraft to nose over.
- No mechanical fault was found in the governor system, and the throttle and linkage were operating within manual limits.
- While the pilot suspected a partial governor failure, no cause for a loss of rotor rpm was identified.
- It is possible that the low rotor rpm warning was triggered because the collective lever was raised during a descent when there was insufficient power margin available due to the high aircraft weight and the 20-25 kt wind conditions.