What happened
On 16 October 1999, a Westland Scout, registration G-BXRL, was conducting a private flight from Baxterly to Bulkington. The crew, consisting of the pilot and two passengers, had previously flown locally before attempting to reach their destination. Upon arriving at the intended hangar in Bulkington, the pilot discovered the hangar was inaccessible due to a parked vehicle, prompting a decision to return to Baxterly.
During the return flight, while cruising at approximately 90 knots near Mancetter, the helicopter experienced a sudden shudder and a leftward yaw. The pilot, perceiving a loss of power, lowered the collective pitch to initiate an autorotation and heard an audio warning. To avoid a funfair and residential buildings located below, the pilot steered the aircraft toward a flooded quarry. During the descent, a 'zero power' torque warning appeared on the instrument panel. The pilot attempted an autorotative landing but flared too late, causing the aircraft to strike the water with significant force and come to rest upside down. The impact destroyed the aircraft.
All three occupants sustained minor injuries. The pilot noted that his shoulder harness was unlatched during the flight, which caused his upper body to move forward during the impact. The crew managed to exit the submerged helicopter through a broken windscreen and swam to the quarry edge, where they were eventually assisted by bystanders.
The investigation
Following the accident, the wreckage was recovered from the quarry approximately one month later. Detailed examination of the Westland Scout at the AAIB facility revealed that the main rotor blades had sustained damage consistent with a water impact while rotating. While the tail rotor gearbox separated from the tail boom due to impact loads, the drive shaft between the engine accessory gearbox and the main rotor gearbox showed a fracture in torsion, suggesting the engine was still running when the rotors hit the water.
Engine inspections showed no pre-existing defects or oil contamination. However, flight testing conducted with a similar aircraft identified a potential operational risk. It was discovered that a small movement of the twist grip throttle could move the power turbine out of its governed range. This could lead to symptoms mimicking an engine failure, particularly for pilots accustomed to the throttle responses of piston-powered helicopters.
Findings
- The pilot inadvertently moved the throttle out of the governed range, creating the appearance of a power loss.
- The pilot's reaction to the initial shudder was to reduce collective pitch, which triggered the torque warning.
- The pilot interpreted the resulting instrument indications as a confirmed engine failure, leading to the decision to perform an autorotative landing.
- The late flare during the final approach to the water surface contributed to the severity of the impact.