Accident Overview
On 13 April 2006 at 1030 hours UTC, an Enstrom 280C Shark helicopter, registration G-BXEE, was involved in an accident at Sandtoft Aerodrome, Doncaster. The aircraft was conducting a training flight with two crew members—an instructor and a student—and no passengers. Both occupants were wearing four-point harnesses and were uninjured.
History of the Flight
The instructor was hover taxiing the helicopter at a height of about 5 feet above grass when over-pitching of the main rotor blades occurred. Over-pitching is a phenomenon where decreasing rotor rpm results in reduced total rotor thrust, and if it occurs in the hover, there is normally insufficient height to restore rotor rpm, forcing a landing. The instructor recognized the blades were over-pitched and took recovery action by lowering the collective and attempting a run-on landing. During the landing, the left skid caught the ground, rolling the helicopter onto its left side and stalling the engine. The aircraft then rolled onto its side. Both occupants vacated the aircraft unaided through the right door.
Contributing Factors
The investigation identified several factors contributing to the accident. The instructor had insufficient power applied, resulting in over-pitching the rotor blades. Additionally, the instructor lacked experience on the Enstrom 280C type, having only recently qualified to fly it. All previous flying experience had been gained on Robinson R22 and R44 helicopters, which are equipped with an engine governor and correlator that automatically match engine rpm to rotor pitch. The Enstrom 280C has neither a governor nor a correlator, requiring the pilot to manually twist the collective-mounted throttle to match engine rpm to power demand. Furthermore, the accident aircraft was not fitted with a low rotor rpm warning device (neither a horn nor a light), although the instructor noted that the helicopter used for his conversion training had a warning horn. At the time of the accident, the instructor was also teaching the student how to hover taxi, which added an element of distraction.
Damage and Injuries
The helicopter sustained substantial damage to the tail, cabin, main rotors, and tail rotor. Both crew members were uninjured.
Conclusion
The instructor had insufficient power applied resulting in over-pitching the rotor blades. A lack of experience on type, an absence of any low rpm warning device, and an element of distraction were all contributory factors. The instructor recognized the blades were over-pitched and took appropriate recovery action, but the left skid caught the ground, rolling the aircraft onto its side.