What happened
On 3 July 2025, an Ikarus C42 FB100 Bravo, registration G-MOOD, was conducting a private introductory flight from Wycombe Air Park. Shortly after departing from Runway 24, the aircraft experienced a complete engine failure at approximately 700 ft. The pilot, following standard procedures, lowered the nose to maintain airspeed and identified a field to the right as a potential landing site, as a line of trees blocked the path straight ahead.
During the attempt to reach the field, the aircraft collided with trees, causing a steep, nose-down impact with the ground. Both the pilot and the passenger sustained serious injuries. A nearby helicopter pilot witnessed the event and landed to assist the occupants with their egress from the destroyed aircraft.
The investigation
The investigation focused on the sudden loss of power. While a mechanical engine failure was ruled out and fuel exhaustion was not a factor, investigators examined the fuel used for the flight. The aircraft had been refuelled that morning using a jerry can containing premium E5 unleaded petrol purchased from a local station.
Laboratory analysis of the fuel remaining in the aircraft's tank revealed a Research Octane Number (RON) of 87.1, which was significantly below the minimum requirement specified by the engine manufacturer. Further testing of a sample from the refueling container suggested the fuel was contaminated with a substance similar to light kerosene, diesel, or jet fuel, with a Motor Octane Number (MON) of only 74.2. Additionally, the investigation noted that other aircraft from the same operator had recently experienced engine issues and found a jelly-like substance in their carburettor bowls after using the same fuel batch.
Findings
- The engine failure could not be definitively proven, but the use of incorrectly graded or contaminated fuel is a primary suspected cause.
- The fuel in the aircraft's tank lacked the necessary octane rating for proper combustion.
- The fuel in the supply container was found to be equivalent to a light kerosene or diesel-type fuel, which would prevent ignition in a spark-ignition engine.
- Vapour lock was considered a secondary possibility due to the high ambient temperature and the use of Mogas, though the pilot's decision-making regarding the landing site was noted as appropriate for the low-level emergency.