Accident Overview
On 10 February 2016, at 1620 UTC, a Bell 206B Jet Ranger II, registration G-OAMI, experienced a sudden and uncommanded loss of altitude while in level flight approximately 3 miles west-northwest of Wycombe Air Park, Buckinghamshire. The helicopter was on a private flight with one pilot and three passengers on board. No injuries were reported among the occupants. The aircraft sustained significant damage, including collapse of the landing gear and failure of the tail boom.
Flight and Pilot Information
The pilot, aged 32, held a Commercial Pilot's Licence and had accumulated 757 total flying hours, of which 77 hours were on the Bell 206 type. In the 90 days prior to the accident, the pilot had logged 39 hours, with 25 hours in the last 28 days. The aircraft was a 1968 Bell 206B Jet Ranger II (serial no. 464) powered by a single Allison 250-C20 turboshaft engine.
Sequence of Events
After departing from Wycombe Air Park, the helicopter was in level flight when it suddenly and unexpectedly began to lose altitude at a high rate. Believing that the engine had lost power, the pilot initiated an autorotation to manage the descent. However, the helicopter touched down with a high rate of descent, resulting in the failure of the tail boom and landing gear.
Investigation Findings
Data recorded by the helicopter's on-board systems indicated that the engine operated normally throughout the entire event, contradicting the pilot's initial belief of an engine power loss. A subsequent limited examination of the helicopter was unable to identify any defect within the engine or flight control systems that could have caused the uncommanded loss of altitude.