What happened
On 5 June 2011, a Jabiru J430, registration G-RCST, was performing a private flight from Eshott, Northumberland, toward a farm strip in Norfolk. While flying through the Newcastle Control Area at approximately 1,200 ft, the pilot observed smoke and fumes entering the cockpit. Simultaneously, the engine oil pressure began to drop rapidly.
Following a MAYDAY call, the pilot prepared for a forced landing. Although the pilot initially intended to land at a specific field, the presence of people in that area necessitated a change in plans. The pilot subsequently performed a landing in an adjacent field characterized by rough, furrowed ground. While the landing was successful and there were no injuries, the aircraft sustained damage to the firewall, the nose landing gear, and the engine.
The investigation
Investigators examined the engine oil cooler, which had been installed shortly before the flight to replace a previously leaking unit. The examination revealed a split in a seam of the new component. Metallurgical analysis showed that the lower plate of the cooler had developed a bulge, leading to a longitudinal fracture in the sheet metal sidewall. This failure was caused by a lack of solder between the lower plate and the corrugated channels during the manufacturing process, which allowed internal oil pressure to deform the metal.
Additionally, the investigation looked into the previously fitted oil cooler, which had been replaced due to a 'weep'. This older unit was found to have developed fatigue cracks in the corners of the lower plate sidewall, which had originated from multiple sites on the internal surface of the chamber.
Findings
- The primary cause of the oil loss was a manufacturing defect in the new oil cooler, where the omission of solder prevented the internal channels from being securely attached to the lower plate.
- The resulting internal pressure caused the lower plate to bulge and eventually fracture the sidewall.
- The previously replaced oil cooler had failed due to fatigue cracking.
- There was no evidence that the manufacturer's stated 175 psi pressure test had been successfully performed on the faulty unit, as the observed bulge would likely have prevented it from withstanding such pressure.