What happened
On 29 June 2003, a modified Ponsford Bensen B8MR gyroplane, registration G-BIGU, was involved in a fatal accident at Shipdham Airfield, Norfolk. The pilot, who had recently completed a gyroplane training course, was performing his first unsupervised flight in the aircraft. Witnesses observed the gyroplane flying at a relatively low altitude, noting a 'porpoising' motion along the runway. During the flight, witnesses reported hearing a loud 'bang' or 'clunk' followed by a sudden change in engine noise. Immediately after this sound, the aircraft pitched nose-down and fell vertically to the ground. The impact occurred in a nearby wheat field, and the 1 fatality was confirmed at the scene.
The investigation
Investigators examined the wreckage and found that the rotor blades had red marks on their undersides, which were consistent with striking the aircraft's rudder. A section of the rudder was found detached and scattered away from the main wreckage. Computer modelling conducted by the University of Glasgow suggested that the aircraft possessed poor longitudinal stability characteristics. The study indicated that at higher speeds, the aircraft could exhibit an unstable pitch response. Furthermore, the investigation revealed that the aircraft had been fitted with a rotor diameter of 23 feet, which was larger than the 22-foot diameter specified in its Permit to Fly. This modification affected the machine's weight, balance, and performance.
Findings
- The primary cause of the accident was the rotor blades striking the rudder, which rendered the aircraft uncontrollable.
- The aircraft's stability was compromised by a thrust line located significantly above the vertical centre of gravity.
- The pilot was experiencing difficulty controlling the aircraft, as evidenced by observed 'porpoising' and previous notes of over-controlling.
- The use of a pump-action control stick likely increased the aircraft's susceptibility to pilot-induced oscillations.
- The installation of a larger rotor than permitted altered the aircraft's handling and weight distribution.