What happened
On 15 March 2025, a Westland Wasp HAS1, registration G-CMBE, was undergoing pre-flight inspections at Marston Doles, Warwickshire. The flight was a private instructional session involving an instructor and a student pilot. While the rotors were running, the crew was performing post-engine start checks, which included cycling the hydraulic system to the 'off' position to verify the continuity and operation of the mechanical flight controls without servo assistance.
As the instructor toggled the hydraulic system switch to the off position, the collective lever reacted with an unexpected and forceful upward movement. This sudden motion caught the instructor by surprise, and he was unable to apply enough downward pressure to arrest the movement. The helicopter lifted approximately 5 to 6 feet into the air and lurched toward a nearby hangar door. Although the instructor attempted to regain control and move the aircraft away from the hangar, the helicopter tipped backward, causing the tail rotor to strike the ground. The main rotor subsequently impacted the ground, resulting in the aircraft rolling onto its side. There were no injuries to the two crew members, but the aircraft suffered severe structural damage to the fuselage, as well as the main and tail rotors.
The investigation
The investigation focused on the cause of the abnormal collective movement. An independent technical assessment of the hydraulic system, rotor head, and flight controls was conducted, which revealed no clear evidence of component failure or system malfunction. However, investigators noted that the single piston hydraulic collective pitch servo jack was found in a fully extended position following the accident. While this could have been a result of the rollover itself, it was noted as an unexpected finding.
Consultations with other pilots experienced with the Wasp and Scout models indicated that while the collective lever is known to move slightly during this specific hydraulic check, the movement is typically limited to a few centimeters and is easily managed by hand pressure. This contrasted sharply with the forceful movement experienced during this incident.