Aircraft and Crew
The accident involved a Robinson R22 Beta helicopter, registration G-BZYE, powered by a single Lycoming O-360-J2A piston engine. The aircraft was manufactured in 2001. The commander, a 48-year-old private pilot, held a Private Pilot’s Licence and had accumulated 378 total flying hours, of which 350 were on type. His recent flying experience included 4 hours in the last 90 days and 2 hours in the last 28 days. One passenger was on board.
History of Events
On 21 September 2008, a student pilot was authorised for a solo flight at Blackbushe Airport to practise hovering and circuits. During pre-start checks, the student did not ensure the throttle was fully closed. When starting the engine, the rpm increased rapidly. The student instinctively closed the throttle and estimated the maximum rpm at 80–85%, though the exact value was not recalled. The engine limit is 2,700 rpm (approximately 105%), and no overspeed, even momentary, is permitted. The student continued with the planned flight and later informed his instructor. The instructor questioned the student and formed the opinion that the student had probably not oversped the engine. The instructor subsequently flew G-BZYE to assess its condition, found all indications normal, and continued instructional flights. A note was placed with the technical log to advise the maintenance organisation about the suspected overspeed. The following day, the commander (a different pilot) planned to fly the helicopter to a maintenance facility for a 100-hour inspection. He reviewed the note but, finding no entry in the technical log, decided to proceed.
The Accident
On 22 September 2008 at 1400 UTC, the commander started the engine normally and hover-taxied to the takeoff point at Blackbushe Airport. All aircraft and engine indications were within limits. During the transition to forward flight, shortly after the helicopter began moving forward, it yawed violently to the right. Manifold pressure increased, and the aircraft started to climb. The pilot lowered the collective lever and applied left pedal to correct the yaw but had difficulty maintaining control. Suspecting an engine governor failure, he levelled the aircraft and attempted a slow running landing. Just before touchdown, applying the collective to cushion the landing caused another yaw and climb, making control very difficult. The pilot stabilised the helicopter and attempted a second landing without cushioning the touchdown. The aircraft landed more heavily than normal and came to a halt. On the ground with the rotor at 100% rpm, the pilot observed manifold pressure varying between 12 and 17 inches and the engine running rough. He advised ATC that the aircraft was safely down and shut down the engine. The passenger sustained minor injuries; the pilot was uninjured.
Post-Accident Inspection
Maintenance personnel inspected the helicopter and found damage to the lower frames, rear undercarriage legs, a crosstube, and both engine side panels, consistent with a heavy landing. Inspection of the engine revealed a broken plastic gear on the left engine magneto, which could account for the rough running and fluctuating manifold pressure. The maintenance organisation had previous experience of this failure, typically associated with an engine overspeed or an inadvertent 'dead cut' (both magnetos turned off while the engine is running). Additionally, evidence showed that the engine cooling fan had moved on its shaft, also consistent with an overspeed. The engine was sent to an approved Lycoming facility for an overspeed inspection, which found clear evidence of an overspeed: all cylinders had excessively worn valve guides and stepped valve springs.
Comments
The instructor and Chief Pilot involved in the chain of events were open about their decisions. They both agreed that, with the benefit of hindsight, a safer course would have been to ground the aircraft and seek engineering advice as soon as they became aware of a suspected engine overspeed. The Chief Pilot subsequently issued a company-wide memorandum reminding instructional staff to treat incidents as a worst-case scenario and not to fly an aircraft after any suspected exceedence until appropriate engineering action is completed.