What happened
On 20 February 2009, a DHC-1 Chipmunk 22A, registration G-BWUV, was performing a private flight departing from Wombleton Airfield in North Yorkshire. After taking off from Runway 29, the aircraft climbed to an altitude of approximately 300 feet when the engine suffered a total loss of power.
In response to the engine failure, the pilot deployed full flaps and attempted an immediate forced landing directly ahead. During the maneuver, the aircraft struck a hedge and a wire fence. The wire fence became entangled in the right undercarriage leg, causing the aircraft to yaw sharply to the right and come to a rapid stop. The impact resulted in the aircraft being damaged beyond economic repair, though the pilot sustained only minor injuries and was able to exit the cockpit without assistance.
The investigation
The investigation focused on the sudden loss of power from the De Havilland Gipsy Major 10 MK2 engine. Examination of the engine components revealed significant issues with the magneto settings. Investigators determined that the left magneto contact breaker failed to open entirely, rendering it incapable of generating a spark. Additionally, the right magneto was found to have been set to open too far, which resulted in a weak and mistimed spark.
Findings
- The engine power loss was caused by a failure in the ignition system.
- The left magneto was non-functional because the contact breaker remained closed.
- The right magneto provided insufficient ignition due to an incorrect setting.
- It is believed that the left magneto setting drifted from its correct position sometime after the pre-takeoff inspections were completed, leaving the engine to rely on the deficient right magneto. This likely led to fouled plugs and a subsequent reduction in engine output.