What happened
On 23 November 2007, a Rans S6-ESD XL (registration G-MZNV) was conducting a private flight from Sandown, Isle of Wight, to Brimpton, Berkshire. While cruising at 1,200 ft amsl, the aircraft's Rotax 503-2V engine failed. The failure was characterized by a smooth but rapid reduction in power. The pilot attempted to restart the engine on four separate occasions, but the engine failed to maintain running power each time.
During the forced landing, the pilot selected a large field of short crop approximately three miles east of Popham. The aircraft touched down halfway into the field, but the nose gear collapsed upon contact with the ground. The nose leg dug into the soft soil, causing the aircraft to overturn and come to rest inverted. Despite the impact, the pilot and one passenger, both wearing three-point seatbelty, sustained no injuries and were able to exit the aircraft through the standard door.
The investigation
Investigators examined the engine and fuel systems to determine the cause of the power loss. They identified a slow fuel leak originating from the tank breather; however, because there was no ignition source nearby, no fire occurred. Fuel pressure measured just before the carburettor remained stable, and sufficient fuel was available for the flight duration.
Because the Rotax 503-2V engine was not equipped with carburettor heating, investigators considered the possibility of carburettor icing. Meteorological data from RAF Odiham indicated a temperature of +5ºC and a dew point of +0ºC. While these conditions suggest a risk of moderate to serious icing according to standard aviation charts, the investigation noted that the engine's configuration draws induction air past the cylinder head. Furthermore, the distributor for the engine reported that while electric heater kits were available, they had received no reports of carburettor icing issues from aircraft using this specific air-drawing configuration.