History of the Flight
G-JAPS, a recently constructed Europa XS, had completed three test flights earlier on the day of the accident, each followed by a thorough inspection. The accident flight, intended as an endurance test, was conducted by a test pilot with the owner as an observer. The aircraft had been fuelled with MOGAS from a local garage and carried approximately 46 litres of fuel. After satisfactory engine runs, the pilot took off from Fishburn. The aircraft performed as expected for about 1 hour 30 minutes. While cruising at 1,500 ft, the engine began to misfire and ran roughly, with engine speed pulsing between 2,000 and 4,000 rpm. When the pilot set the throttle to 2,000 rpm, operation improved, but reopening the throttle caused the speed to pulse again and reduce toward 2,000 rpm. The pilot cycled the fuel supply valve from MAIN to RESERVE, switched on the auxiliary fuel pump, set the electric constant speed propeller to manual, and briefly deselected the turbo control unit, all with little effect.
The engine no longer provided enough power to maintain altitude, so a forced landing was prepared. A field near Hulam Farm was selected, and an approach was made with 10° flap, trimmed for 75 kt, with full flap selected late. The field had an uneven surface. During the flare, the left wingtip contacted the ground simultaneously with the main landing gear, causing the aircraft to flip inverted before coming to rest. There was no fire, and both occupants, wearing four-point harnesses, exited with only minor injuries.
Engine and Fuel System Description
G-JAPS was equipped with a Rotax 914 Turbo piston engine, a four-cylinder horizontally opposed engine with two balanced carburettors, each supplying two cylinders, fed by a turbocharger controlled electronically via a turbo control unit, servo, and pushrods that operate the wastegate. The fuel system comprised a single inverted horseshoe-shaped fuel tank in the fuselage with a 65-litre capacity. One side of the horseshoe served as the main tank, the other as an 8.5-litre reserve. Fuel from both tanks passed through a three-way valve selectable to MAIN, RESERVE, or OFF, then through two electric pumps (main and auxiliary), fuel filters, a fuel flow sensor, and a gascolator before reaching the carburettors. Unused fuel returned to the tank via an additional fuel flow sensor.
Examination Findings
Following the accident, the owner removed both carburettors for detailed examination at a facility specialising in Europa aircraft. Both carburettors contained uncontaminated fuel in their float chambers. The left carburettor revealed no defects. However, the right carburettor had a loose main fuel jet needle within its piston housing, allowing it to travel. No other defects were found. Subsequent discussions with the engine manufacturer indicated that a floating main jet needle would enrich the fuel-air mixture but should not cause an engine operation problem. However, the effect of the needle floating cyclically or vibrating up and down in flight was not established.
The AAIB conducted a full examination of the engine and fuel system. The engine was free to turn with no signs of catastrophic failure. Spark plugs, cylinders, ignition system, and compression checks revealed no pre-existing defects. A functional test of the turbocharger system was satisfactory. Fuel filters were clean, and system flow tests showed adequate fuel delivery. The aircraft was equipped with an R-DAT recording engine parameters every six minutes; review showed no previous exceedences or significant variation.
The only anomaly discovered was the loose main fuel jet needle in the right carburettor, which likely enriches the mixture in two cylinders. While this should not have caused the symptoms experienced, the possibility that the needle could float cyclically and affect normal operation could not be entirely dismissed. Carburettor icing was considered but deemed unlikely due to the turbocharger raising induction air temperature. Vapour lock was also considered but thought improbable given the flight duration and previous incident-free flights.
Conclusion
Despite a thorough inspection of the engine and fuel system, the exact cause of the engine failure was not determined. The presence of a loose main fuel jet needle in the right carburettor was the only anomaly found; this defect likely enriched the mixture in two cylinders, but the possibility that it could cyclically affect operation could not be entirely dismissed.