What happened
On 19 May 2019, a Team Minimax 91, registration G-BZOR, was cruising at 2,000 ft when the engine began misfiring and lost power. The pilot noted increased vibrations and a lack of throttle response, suggesting a cylinder failure. Because the aircraft could no longer maintain its altitude, the pilot prepared for an emergency landing.
As the aircraft was not under air traffic control service, the pilot chose to focus on flight controls rather than transmitting a distress call. After passing over a wooded area, the pilot identified a suitable landing spot on an uphill slope within open heathland. To manage the risk of a tight turn into the wind during the final approach, the pilot increased the airspeed from 55 to 75 mph to maintain a safer stall margin.
The aircraft touched down gently into a light north-north-easterly breeze. However, as the aircraft stopped, the front axle became caught in the heather, causing the aircraft to tip forward onto its nose. The incident resulted in no injuries, though the airframe sustained a dented cowling and a broken brake cable.
The investigation
The investigation examined the engine's condition and the pilot's actions. The engine, a Rotax 447, had recently undergone significant maintenance, including a rebuild and the installation of a new ignition module. The fuel used was MOGAS, which had been correctly diluted with oil and filtered.
Upon inspection of the aircraft, the carburettor float bowl contained uncontaminated fuel, and the spark plugs were found to be clean and functioning correctly. Diagnostic testing was subsequently performed on the ignition system.
Findings
- The engine failure was caused by a faulty ignition stator that was breaking down under load.
- The pilot's decision to prioritise aircraft control over radio communication assisted in the successful landing.
- The pilot's use of a higher approach speed provided a necessary margin for the tight turn required by the terrain.