What happened
On 10 June 2018, a Just SuperSTOL XL, registration G-SSXL, was conducting test flights near Barton Aerodrome, Manchester, to prepare for its Permit to Fly. The flight was being conducted by a testing pilot and the aircraft owner. During the second flight of the day, while at approximately 500 ft agl, the engine displayed an excessively high exhaust gas temperature (EGT) warning. Following this, the engine gradually lost power and failed at an altitude of about 800 ft agl.
The crew attempted a forced landing in a nearby ploughed field. The testing pilot took control of the aircraft at roughly 200 ft agl. The aircraft landed heavily without flaps extended, causing the landing gear to collapse and the aircraft to rest on its underside. The impact resulted in one serious injury to the testing pilot and minor injuries to the owner. The aircraft sustained damage beyond economical repair.
The investigation
The AAIB examined the engine's Engine Control Unit (ECU) data logger. While the data was limited, it revealed that the inlet air temperature had reached 76°C, which exceeded the manufacturer's recommended in-flight maximum of 40°C. The investigation also noted that the ambient temperature was 24°C, which was above the LAA's recommended limit for using Mogas fuel.
Investigators also reviewed the flight dynamics. Due to the low altitude at which the testing pilot took control, it is believed the aircraft was not stabilized, leading to a stall and a subsequent firm landing.
Findings
- The engine failure was likely caused by fuel vapour lock resulting from high temperatures within the engine compartment.
- The inlet air temperature recorded by the ECU was significantly higher than the manufacturer's specified limit.
- The heavy landing was likely due to the aircraft stalling at a low altitude during the forced landing sequence.