What happened
On 28 November 1998, a DHC Dash 7-102, registered VP-CDY, was conducting a performance-related test flight in UK airspace. The flight, which originated from Guernsey, was intended to evaluate the aircraft's climb capabilities following an engine change. During the descent to 5,000 feet, the crew shut down the number one engine and feathered its propeller as part of the test configuration.
As the aircraft descended, the airspeed decreased. While the autopilot was still engaged, the aircraft reached a state of stall. Flight data indicates that the aircraft began to rotate rapidly to the left, with witnesses describing a spiral or spinning motion. Despite the application of power to the remaining three engines, the aircraft entered a high-rate descent and struck the ground on the southern slopes of Dartmoor. The impact was followed by a significant post-crash fire that destroyed much of the wreckage. Both the pilot and the first officer sustained fatal injuries.
The investigation
Investigators examined the wreckage and recovered both the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). Although the CVR was non-functional for the duration of the accident flight due to seized bearings, the FDR provided a detailed reconstruction of the flight parameters.
Analysis of the FDR revealed that the aircraft was not correctly configured for the intended 3-engine climb; specifically, the flaps remained retracted rather than being set to 25 degrees. The investigation also utilized a full flight simulator to model the aircraft's behavior. The simulator confirmed that the autopilot, while attempting to maintain level flight, applied significant nose-up trim, which would have created high longitudinal control forces.
Findings
- The aircraft was not in the correct configuration for the scheduled test, as the flaps were not extended to the required 25 degrees.
- The autopilot remained engaged through the onset of the stall, and the crew failed to respond adequately to the stick shaker warnings.
- The application of asymmetric power from the three operating engines during the stall likely induced the rapid left-hand roll and subsequent rotation.
- The pilot's manual input of full aft control column during the descent was a significant factor in the inability to recover from the stall.
- The lack of a functional CVR prevented investigators from determining the exact cause of the crew's lack of coordination or potential distractions.