What happened
On 11 May 1999, an AS 355F1, registration G-BXBT, was conducting a private training flight at Kidlington Airfield. The flight involved a simulated hydraulic failure maneuver. During the approach to a hover, the student pilot lost control of the aircraft's yaw. The instructor intervened to take control and successfully restored yaw stability; however, during this transition, the instructor's hand slipped from the collective lever.
As a result of the instructor losing his grip, the collective lever dropped by approximately three inches. This caused the helicopter to descend roughly 6 feet, resulting in a heavy impact with the ground. The aircraft sustained damage to the landing gear, along with distortion and creasing to the tailboom. There were no injuries to the two crew members on board.
The investigation
The investigation was based on the aircraft accident report submitted by the pilot. The inquiry focused on the sequence of events during the handover of controls between the student and the instructor. It was noted that the student may not have immediately relinquished control when instructed to do so, which contributed to the instructor's loss of grip on the collective lever during the recovery attempt.