History of the Flight
The aircraft, a Jabiru SK registered as G-JABA, was operating under a UK Permit to Fly. The pilot, holding a Private Pilot's Licence with 188 total flying hours (20 on type), departed from Whiterashes Airstrip with approximately two hours of fuel (34 litres) to practice circuits. On the downwind leg of the initial circuit, engine power was reduced to approximately 2,000 rpm. While performing pre-landing checks but before applying carburettor heat, the engine hesitated briefly and then stopped. The pilot trimmed for best glide speed but assessed that altitude was insufficient to return to the airstrip. A forced landing was executed in a crop field about 1 nautical mile west of the airstrip. During the approach, the pilot attempted to restart the engine using the electric fuel pump and starter, but the engine did not start. The field surface was rough beneath the crop, and the aircraft sustained damage to the nose leg, left main landing gear, propeller, and left wingtip. The pilot was uninjured.
Meteorological Conditions
An aftercast from the Met Office estimated surface conditions at the accident location: temperature +18°C, dewpoint +14°C, and wind 340° at 5 kt. At 1,000 ft altitude, conditions were estimated as temperature +18°C, dewpoint +10°C, and wind 250° at 5–10 kt. According to the carburettor icing chart, these conditions were favorable for 'moderate icing – cruise power' and 'serious icing – descent power'.
Engine Examination
The day after the accident, the pilot examined the engine and found fuel in the carburettor float chamber. The engine turned freely, the ignition system functioned normally, and no fuel leaks were observed. Sufficient fuel for the flight remained in the main tank. A subsequent strip inspection did not reveal any defects that would have contributed to the engine failure.
Discussion
The prevailing meteorological conditions at the time were favorable for the formation of serious carburettor icing at descent power settings. Lack of application of carburettor heat and subsequent carburettor icing were the most likely causes of the engine failure. A contributory factor in the accident was the presence of crop in the field selected for the forced landing, which obscured the field's underlying rough surface condition.
The CAA's Safety Sense Leaflet 14, 'Piston Engine Icing', provides guidance on these hazards, noting that carburettor heat should be applied early enough before descent and remain fully applied during descent, as the engine is more susceptible to icing at low power settings. The downwind check should include the cruise carburettor heat check.