What happened
On 27 June 2004, an X'Air V2(2), registration G-CBTY, was performing a training circuit near Newtownards, Northern Ireland. During the downwind checks, the instructor noted that the Simonini Victor II engine was operating normally with Exhaust Gas Temperature (EGT) within expected limits. Following the first touch-and-go, the aircraft climbed to approximately 300 feet when the engine stopped abruptly.
The pilot performed a forced landing into a field containing three-foot-high crops. As the main wheels entered the vegetation, the aircraft pitched forward, causing the nose landing gear to dig into the soft ground and the aircraft to pitch into an inverted position. There were no injuries to the two crew members on board, and no fire occurred during the event.
The investigation
The AAIB examined the engine and the aircraft's maintenance history. The investigation revealed that the aircraft had been stationary for several months prior to the accident, and the engine inhibition procedures recommended by the manufacturer had not been performed. Before the flight, the aircraft owner had added a cup of water to the coolant system.
Upon inspection of the engine, investigators found two burn holes in the rear cylinder head that penetrated the liquid cooling jacket and the head-to-block seal. The elastomeric O-ring seal showed signs of thermal degeneration. Furthermore, the carburettor float chambers contained liquid that was primarily composed of water. Metallurgical examination of the engine's roller bearings showed evidence of corrosion caused by prolonged exposure to an oxygen-carrying liquid within the crankcase.
Findings
- The engine failure was caused by a loss of coolant, which allowed hot gases to burn through the cylinder casing.
- The engine's elastomeric seals had suffered thermal degeneration, leading to a leak that allowed liquid to enter the crankcase.
- The presence of water in the crankcase and carburettor float chambers contributed to the corrosion of the engine's roller bearings.
- The engine had not undergone the manufacturer-recommended lubrication and storage procedures during its period of inactivity.