History of the Flight
The pilot and his wife completed an uneventful flight from a private site near Southampton to Haverfordwest Airfield. Weather conditions were good, with a south-westerly wind at about 20 kt, visibility exceeding 10 km, and broken cloud at about 2,000 ft. The helicopter was positioned on the downwind leg for a left-hand circuit to Runway 21. A normal approach was made to Runway 21 with a surface wind from 220° at 10-15 kt. The helicopter was hover taxied along the runway and turned right along the taxiway/parking area towards the refuelling point. As the helicopter neared the hangars, it turned sharply, which the pilot tried to correct with some effect. He could not recall in which direction the helicopter turned but decided to try to turn it into wind and take off. On raising the collective lever, the helicopter did not respond, and suspecting a technical problem, the pilot elected to perform an immediate landing. The landing gear contacted the ground, and the helicopter bounced, rolling to the left. The main rotor blades contacted the grass surface to the east of the taxiway, shearing the main rotor mast. The main rotor head and blades detached, and the fuselage came to rest on its left side. There was no fire, and the pilot carried out the emergency shut down drills. Both occupants were uninjured and vacated the helicopter through the pilot's door on the right side. The airfield Rescue and Fire Fighting Service promptly attended the scene.
Eyewitness Accounts
An instructor pilot in a Cessna 150, who had been in radio contact with the Bell 206 pilot and had just landed, described the helicopter as in a hover taxi when it became unstable, pitching up and down and rising and descending. Although he could not be certain, he believed the helicopter yawed rapidly to the left before impacting the grass. A second witness, a private pilot who also flew a Bell 206, saw the helicopter hover taxiing along the taxiway and described the same unstable pitching and rolling motion. He saw the helicopter descend rapidly from a high hover taxi, with the right skid touching before the helicopter bounced some five feet back into the air and then descended onto its left side, the main rotor blades striking the ground. During these manoeuvres, the helicopter rotated approximately 180° to the right.
Analysis
The investigation could identify no definite cause for the accident. However, when turning right off the runway, the helicopter hover taxied in a northerly direction along the taxiway. The surface wind was from the left rear quarter direction. The weather-cocking effect induced a yawing motion which, when combined with the airflow under the horizontal stabiliser pitching the helicopter nose down, created difficult flying conditions for the pilot. In attempting to maintain control, the pilot was probably making large control movements associated with the pitching and rolling reaction of the aircraft described by the witnesses. His attempt to take off by raising the collective pitch control did not produce any significant climb or acceleration from the helicopter, likely due to using a high power setting in the downwind condition, which did not produce the normal take-off reaction. The bounce occurred due to a positive lowering of the collective pitch control in order to land immediately, which produced a high rate of descent and an excessive left roll angle, permitting the main rotor blades to strike the ground.