What happened
On 5 May 2017, an AS350 B3e helicopter, registration G-MATH, was conducting type conversion training at Wycombe Air Park. The flight crew consisted of an instructor in the left seat, a trainee pilot in the right seat, and a second trainee acting as a passenger in the rear. The objective of the session was to practice procedures for a hydraulic failure.
To simulate the failure, the instructor followed the manual's procedure to depressurise the hydraulic system. During the first approach, the instructor intervened to perform a go-around after becoming dissatisfied with the trainee's handling of the aircraft's speed and yaw. A second attempt was made, but during a left-hand turn on the downwind leg, the aircraft entered a steep bank. The instructor attempted to apply right cyclic input, but the helicopter rolled beyond 90° and struck the ground. The impact caused extensive damage to the aircraft. The trainee pilot in the right seat sustained fatal injuries, while the instructor and the passenger suffered serious injuries.
The investigation
The AAIB examined flight data and cockpit video recorded by an onboard system. The investigation focused on the control characteristics of the AS350 B3e when the hydraulic system is unpressurised. In this state, the mechanical control forces required to maneuver the aircraft increase significantly.
Investigators analyzed the second go-around, noting that as the angle of bank increased, the instructor's physical input appeared insufficient to arrest the roll. The investigation also looked into the clarity of the manufacturer's flight manual regarding the limitations of flying without hydraulic assistance, particularly during low-speed maneuvers and go-arounds.