What happened
On 6 January 2012, a Robinson R22 Beta, registration G-CHZN, was conducting a private flight from Manston to Fenland. The pilot, an experienced fixed-wing flyer with significant helicopter experience, was navigating through Cambridgeshire. At approximately 11:21, the aircraft entered the Mildenhall Military Aerodrome Traffic Zone near Ely.
Witnesses on the ground observed the helicopter performing a sudden left roll. One observer reported hearing a sharp 'pop' sound, similar to a paper bag being struck, followed by the sight of objects detaching from the aircraft. The helicopter then fell inverted to the ground. The impact occurred in a field approximately two miles southwest of Ely, resulting in one fatality and the total destruction of the aircraft.
The investigation
Investigators examined radar data from Stansted, Debden, and Cambridge airports, alongside GPS logs and radio communications. The radar showed no other aircraft in the immediate vicinity that could have caused wake turbulence, and the weather was generally good with high visibility.
Analysis of the aircraft's GPS unit provided a track log of the flight, though the unit's altitude recording function was unavailable due to power loss during the crash. The investigation also reviewed the pilot's medical history and the mechanical condition of the rotor head. While the pilot had an undiagnosed medical condition that could cause intermittent symptoms, there was no evidence of an acute episode during the flight. Furthermore, no evidence of engine issues or carburettor icing was found.
Findings
- The accident was caused by main rotor divergence, which led to mast bumping.
- This sequence of events caused the two main rotor blades to strike the airframe and subsequently separate from the rotor head.
- There was no evidence of external interference from other aircraft or significant turbulence.
- The pilot remained conscious at the time of impact, as evidenced by a laceration on his hand suggesting he was gripping the controls.