What happened
On 14 June 2009, a Rotorway 162F helicopter, registration G-JONG, was performing a private flight from Popham towards Barton Aces. While cruising at 1,800 ft approximately 5 nautical miles west of Popham, the engine stopped abruptly without warning.
The pilot immediately initiated an autorotation, reducing airspeed to 65 mph and selecting a landing site on soft ground near Bullington Cross on the A303. The pilot executed a flare approximately 30 ft above the ground. During the landing, the aircraft pitched forward, causing the main rotor blades to strike the surface. The helicopter then rolled onto its right side. The pilot sustained minor injuries and was able to exit the aircraft through the left door.
The investigation
The investigation involved a strip examination of the engine and a detailed metallurgical analysis of its components. Investigators found that the engine would not turn freely, and there was no movement of the valve gear when the crankshaft was rotated.
Subsequent disassembly under AAIB supervision revealed that the aluminium gear responsible for driving the camshaft had lost teeth over nearly a quarter of its circumference. This failure caused the camshaft to de-synchronise from the crankshaft. The resulting impact from the connecting rods broke the camshaft into four separate pieces. Metallurgical examination using scanning electron microscopy showed that the aluminium gear possessed an extremely poor casting quality, characterized by significant porosity and surface voids.
Findings
- The primary cause of the engine failure was the failure of the aluminium camshaft drive gear teeth.
- The gear teeth failed due to inherent material weaknesses caused by a poor-quality casting, which featured extensive internal voids and surface flaking.
- The loss of synchronisation between the camshaft and crankshaft allowed the connecting rods to strike the camshaft, resulting in its fragmentation.
- The gear failure occurred well before the 250-hour service life limit previously established for such components, indicating a manufacturing defect rather than wear or fatigue.