What happened
On 14 July 2002, a Gazelle HT Mk2, registration G-BZOS, was preparing for a private flight from Gaydon, Warwickshire, to Elstree, Hertfordshire. The aircraft was positioned on a grass helipad facing approximately 350° in light, northwesterly winds.
Shortly after lifting off, the helicopter began to yaw to the left. Although the pilot attempted to correct the movement with right pedal, the rate of yaw increased. As the aircraft reached a 180° heading, the rotation became too rapid for the pilot to manage. In an attempt to stabilize the aircraft, the pilot applied right cyclic, which caused the helicopter to roll to the right. This resulted in the main rotor blades striking the ground. The impact caused the helicopter to land on its side, resulting in the aircraft being damaged beyond economic repair. All four occupants (one crew and three passengers) evacuated the wreckage without injury.
The investigation
Investigators examined the wreckage at a maintenance facility, but no mechanical faults were identified in the helicopter. The investigation focused on the phenomenon of rapid yaw development in light wind conditions, a known issue for this aircraft type.
Technical documentation, including Eurocopter Service Letters and the Military Aircraft Manual, highlights that the Gazelle's fenestrone design can lead to sudden, high yaw rates with minimal pedal input. The investigation also noted that the aircraft's hydraulic damper requires the pilot to apply and hold significant force to achieve maximum pedal deflection. Furthermore, the investigation considered the potential for passenger interference with the flight controls, noting that the extendable footrests and removable controls could allow an occupant to inadvertently affect the pedals.
Findings
- The primary cause of the accident was the rapid development of a high yaw rate during the takeoff phase.
- The pilot's lack of experience on this specific type was a contributing factor, as the aircraft's clockwise rotor rotation and pedal requirements differ from many training helicopters.
- The pilot was unable to apply the necessary amount of right pedal to counter the left yaw before the rotation became uncontrollable.