History of the Flight
On 1 August 2018 at 1248 UTC, a Robinson R22 Beta (G-OODX) was on a private flight from Culworth, Northamptonshire, to a private site near Worcester. The pilot, who held a Private Pilot's Licence with 220 hours total flying experience (100 on type), had hired the helicopter from Denham Aerodrome earlier that day. After two uneventful flights, he took off from Culworth at 1218 hrs. During the cruise at 800 ft and 80 kt, a sudden bang was heard, the helicopter yawed aggressively to the left, the low rpm horn activated, and the clutch light illuminated. The pilot established autorotation at 60 kt, then reduced speed to 30 kt to reach a suitable field. He pulled the clutch circuit breaker due to the prolonged clutch light. As the helicopter neared the ground, the pilot flared, but the descent rate was not sufficiently arrested, causing the tail to strike the ground, followed by the skids. The helicopter rotated forward one or two times before coming to rest. Both occupants exited with minor injuries.
Examination
The AAIB did not attend the site but authorised the operator to photograph and recover the wreckage. Examination at the operator's premises confirmed extensive damage, precluding assessment of pre-impact pulley alignment. Both drive belts were missing; a search using a drone and a search dog located one belt in a field months later. Small fragments of the other belt were found in the wreckage. The recovered belt showed a tensile overload failure without evidence of degradation or misalignment. The fragments of the second belt were eroded, consistent with operation while not aligned in the pulleys. The cause of the belt failures was not determined.
Pilot Information
The 46-year-old pilot held a Helicopter Private Pilot's Licence with Robinson R22 and R44 ratings, valid until 31 March 2019. His last flight in an R22 prior to the accident was in May 2018. In 2018, he had flown approximately 75 hours in fixed-wing aircraft and 19 hours in rotary-wing aircraft.
Weather
The pilot reported CAVOK conditions, temperature 20°C, and surface wind from 200° at 8 kt. A Met Office aftercast confirmed benign weather with light south-westerly winds, visibility of 10 km or more, and no significant cloud below 5,000 ft.
Recorded Data
Data from a navigation app showed the helicopter's ground track, groundspeed, altitude, and vertical speed during the autorotation. The pilot descended at an indicated airspeed of about 60 kt initially, reduced to 30 kt, then increased back to 60 kt. At approximately 60 ft above ground, groundspeed was 60 kt, then reduced as the flare was executed.
Aircraft Information
The Robinson R22 uses a double belt system to transmit drive from the engine to the rotor system. The belts are tensioned by an electric actuator that moves the tail rotor drive shaft vertically, functioning as a clutch. The cockpit has a clutch light that illuminates when the actuator operates. The pilot's operating handbook notes that the clutch light may come on momentarily during retensioning, but if it flickers or stays on for more than 10 seconds, the pilot should pull the clutch circuit breaker and land as soon as practical.
Laboratory Examination
Laboratory examination of the recovered belt found it complete but fractured, with no evidence of wear or damage indicating misalignment or foreign object contamination. The failure was consistent with tensile overload. The fragments of the other belt showed grinding wear, suggesting it operated while not aligned.
Autorotation
The R22 pilot's operating handbook provides a procedure for power failure above 500 ft: establish 65 kt, maintain rotor rpm between 97% and 110%, and perform a cyclic flare to arrest descent before landing. The helicopter has a low-inertia rotor system; most autorotation energy is stored in forward momentum.