What happened
On 20 October 2007, a Savannah Jabiru, registration G-CEED, was conducting a private flight near Mergate Hall, Bracon, Norfolk. Approximately five minutes after departure, the pilot performed a standard 'FREDA' check. While all engine indications initially appeared normal, the pilot soon observed smoke entering the cabin. Within less than a minute, the engine seized.
The pilot successfully established a glide and performed a smooth approach into a nearby agricultural field. Due to the rough nature of the terrain, the nose landing gear folded backwards upon impact, causing slight damage to the engine cowling and forward fuselage. The pilot and passenger exited the aircraft without injury, and no fire occurred.
The investigation
An engineering examination of the Jabiru 2LL engine was conducted under the supervision of the AAIB. Metallurgical analysis performed by QinetiQ revealed that the No 3 piston had suffered a burn-through from top to bottom. The investigation also found evidence of piston seizure and overheating in the cylinders, with significant heat discolouration noted on the crankshaft and connecting rod bearings.
Investigators found that the engine had been configured with 'lean burn' jets in the carburettor, following Jabiru Service Letter JSL 002-1, which was intended to improve fuel economy. This investigation was conducted alongside parallel investigations into similar engine failures in other aircraft, including G-CEFY and G-JAAB.
Findings
- The primary cause of the engine failure was pre-ignition in the No 3 cylinder, which led to the piston crown burning through.
- Excessive heat likely caused the piston rings to seize in their grooves, which subsequently allowed engine oil or vapour to enter the combustion chamber, contributing to the pre-ignition.
- The engine had been modified with lean-burn carburettor jets, a configuration that may have contributed to the overheating.
- There was no evidence of significant oil leaks, fuel contamination, or mechanical failure of the exhaust valves.