What happened
On 15 May 2004, a Taylor Titch, registration G-BABE, was conducting a private pleasure flight from Netherthorpe Airfield. Approximately five minutes after departure, the pilot noticed a sudden drop in engine power. Suspecting the presence of carburettor icing, the pilot engaged the carburettor heat, but this action failed to restore performance. While the engine appeared to be running smoothly, the power output remained significantly diminished. After a momentary, brief increase in power, the engine suffered a complete loss of power.
With the engine inoperative, the pilot attempted to select a suitable landing site. The initial approach to a chosen field was too high, prompting a change in plan to a second field. However, the aircraft's glide performance exceeded expectations, leaving the pilot too high for the second site and necessitating a third field selection. Upon touchdown, the aircraft nosed over and came to rest in an inverted position. The pilot, who was wearing a four-point harness, escaped through the broken canopy after shutting off the fuel and electrical systems. The pilot sustained minor injuries.
The investigation
Following the accident, the pilot, who is also an aircraft engineer, disassembled the carburettor to identify the cause of the power loss. During this process, a small aluminium fragment was discovered within the float bowl. This piece of debris was too large to have bypassed the carburettor inlet filter, which was found to be clean. The physical characteristics of the fragment suggested it had been crushed against the needle valve.
Findings
- The engine power loss was caused by an aluminium fragment obstructing the needle valve.
- The fragment was likely already present within the float bowl.
- The obstruction of the needle valve would have either starved the engine of fuel by preventing it from entering the float bowl or caused an excessively rich mixture by allowing the bowl to overfill.
- Both scenarios would result in the severe reduction of available engine power observed during the flight.