History of the Flight
The flight was an introductory flight for a passenger with no light aircraft experience. The pilot performed a pre-flight inspection, including a fuel dip and water check, and conducted power checks after engine start with no abnormalities noted. Approximately 15 to 20 minutes after engine start, takeoff from Runway 24 at Wycombe Air Park commenced. The takeoff was normal. At 300 ft, the pilot switched off the fuel pump and retracted flaps; at 500 ft he reduced power slightly. Shortly after, at about 700 ft, the engine ran down smoothly and stopped.
The pilot lowered the nose, informed the airfield radio operator of his intention to land in a field, but did not declare a MAYDAY. He switched the fuel pump back on but did not attempt a restart or other drills, focusing on maintaining airspeed. He considered landing straight ahead impossible due to a line of trees and aimed for a field to the right. Confident of a successful landing, the aircraft collided with trees at the edge of the field, pitching the nose down and resulting in a steep impact. A helicopter pilot witnessed the accident and landed to assist both occupants, who were seriously injured.
Aircraft and Fuel Information
The aircraft was a 2015 Ikarus C42 FB100 Bravo, registration G-MOOD, powered by a Rotax 912ULS four-stroke engine. The engine manufacturer specifies fuel with minimum Motor Octane Number (MON) of 85, Research Octane Number (RON) of 95, and Anti Knock Index (AKI) of 91. The aircraft was fueled that morning from a jerry can containing premium E5 unleaded petrol (Mogas) purchased from a local petrol station four days prior. The fuel containers were used only for the school's C42 aircraft. The quantity of fuel added could not be verified.
Examination
The company responsible for maintenance examined the aircraft and found no physical cause for the engine failure. The operator arranged laboratory analysis of a fuel sample from the aircraft's tank. The report indicated no contamination or water, ethanol content below 2%, but a RON of 87.1—significantly lower than specified. A second sample, believed to be from the source container, was analyzed by another laboratory, indicating the fuel was equivalent to light kerosene, diesel, or jet fuel, with a MON of 74.2, unsuitable for spark ignition engines. Shortly after this accident, another aircraft from the same school experienced engine problems during takeoff but landed with minor damage. Examination of all school aircraft revealed a jelly-like substance in the carburettor bowls of three aircraft that had been fueled from the same batch as G-MOOD.
Meteorology
Weather was good with light and variable wind, visibility 7–10 km, and temperature 24°C.
Analysis and Conclusion
The cause of the engine failure could not be positively determined, although mechanical failure and fuel exhaustion were ruled out. Fuel assessments suggested that the fuel supplied may have been of lower octane than specified or contaminated with diesel, kerosene, or jet fuel, which would prevent ignition. Another potential cause was vapour lock, risk factors for which included the use of Mogas and high temperature. The pilot's focus on aircraft control avoided a stall/spin scenario. The aircraft struck trees and the ground, seriously injuring both occupants.
Safety Actions: The operator purchased a bowser to supply its aircraft with UL91 fuel.