What happened
On 19 July 2009, a kit-built Spitfire Mk 26, registration G-CEPL, was conducting its first test flight near Bulphan, Essex. The aircraft, powered by a Jabiru 5100A engine, was being operated for private use by a pilot with significant flight experience but no previous time on this specific type.
During the climb, the pilot noticed smoke and fumes entering the cockpit from the exhaust stubs. In an attempt to manage the situation, the pilot reduced power and adjusted the carburettor heat. However, as the aircraft continued to climb, the engine power decreased significantly, and the pilot was unable to maintain altitude. The engine eventually failed completely.
In an attempt to land, the pilot selected the landing gear to the down position. While the right gear deployed successfully, the left gear remained retracted. Despite attempts to use the emergency disconnect mechanism, the left gear failed to extend. The pilot subsequently performed a forced landing in a ploughed field. During the touchdown, the right landing gear collapsed, causing the aircraft to yaw and slide before coming to rest. The pilot sustained minor injuries.
The investigation
An investigation by the LAA and the AAIB examined the engine and the landing gear systems. Technical analysis of the engine revealed significant internal damage, including burned pistons and cylinder heads. The investigation found that the cylinder head temperature (CHT) sensors had been installed incorrectly, beneath the cylinder head bolts rather than beneath the spark plugs. This error caused the gauges to provide grossly inaccurate, low temperature readings, masking the true heat levels within the engine.
Regarding the landing gear, while the exact cause of the left gear's failure to extend was not definitively proven, the symptoms suggested that the mechanical uplock pin failed to withdraw, likely due to a tight fit within its receptacle.
Findings
- The engine failure was caused by detonation of the fuel/air mixture and subsequent overheating, which led to piston burn-through and valve damage.
- The engine was running with an excessively lean mixture, likely due to the carburettor settings being optimized for a fixed-pitch propeller rather than the installed variable-pitch propeller.
- Monitoring of engine temperatures was compromised because the CHT sensors were improperly installed, providing uselessly low readings.
- The installation of a free-flow exhaust extractor necessitated a richer mixture setting than what was provided.
- The left landing gear failed to deploy because the uplock pin likely failed to retract.