What happened
On 2 February 2005, a Beagle B121 Series 1 Pup, registration G-AXNL, was conducting a private flight from White Waltham to North Weald. While flying near Potters Bar, the pilot experienced a sudden reduction in engine power accompanied by fluctuations in fuel pressure. Despite attempts to rectify the issue by using the electric fuel pump, switching to an alternate fuel tank, and applying carburettor heat, the engine performance remained unreliable.
As the aircraft was flying over a densely populated area of North London, the pilot determined that reaching Elstree Aerodrome was unsafe. After transmitting a MAYDAY message, the pilot identified a suitable landing site in a field near Holly Hill Farm. The landing on the upward-sloping ground initially appeared successful; however, as the aircraft rolled, the nose wheel sank into the soft earth. This caused the aircraft to pitch forward and somersault, coming to rest upside down. The aircraft sustained significant damage to the nose, fin, and upper fuselage, and fuel leaked from the wings. The pilot escaped the wreckage without serious injury.
The investigation
Investigators examined the aircraft at a maintenance facility in Sywell. The inspection of the fuel, ignition, and induction systems revealed no mechanical defects capable of causing the power loss. Both wing tanks contained fuel, and the carburettor bowl was found to be full of uncontaminated fuel. While investigators could not definitively rule out a temporary blockage in the carburettor metering passages, no evidence of a mechanical failure was found.
Meteorological data indicated that at the time of the flight, the temperature was 6°C with a dew point of -1°C. These conditions are highly conducive to the formation of ice within a carburettor.
Findings
- The engine power loss was likely caused by carburettor icing.
- Atmospheric conditions (6°C temperature and -1°C dew point) presented a significant risk for moderate to severe icing at any power setting.
- It is possible that the application of carburettor heat was insufficient in duration to clear the intake restriction.
- The aircraft's nose wheel dug into soft ground during the landing roll, causing the inversion.