History of the Flight
On 5 June 2011, at approximately 1704 hours UTC, a Jabiru J430 (registration G-RCST) departed from Eshott, Northumberland, for an intended flight to a farm strip in Norfolk. The aircraft was operating in the Newcastle area when, while overhead Blyth wind farm Visual Reporting Point at an altitude of 1,200 ft, smoke suddenly appeared inside the cockpit. The pilot observed that the engine oil pressure was dropping rapidly. He made a MAYDAY call to Newcastle ATC, who monitored the aircraft on radar and alerted emergency services.
The pilot turned the aircraft westward and prepared for a forced landing. During the approach to a chosen field, he noticed people in the landing area and was forced to select an adjacent field with a tail wind component. The landing was successful, but the rough field surface, consisting of ridges and furrows, caused damage to the nose landing gear and the firewall to which it was attached.
Investigation
Examination revealed that a large quantity of oil had been lost through a split along a seam at the rear of the engine oil cooler. This component was new, having been fitted immediately prior to the accident flight after a 'weep' was discovered in the previously fitted unit. Some oil had dripped onto the exhaust system, generating smoke that entered the cockpit.
The pilot noted that the lower plate of the oil cooler had developed a bulge since installation. Both the failed cooler and the previously fitted unit were examined by a metallurgist. After cleaning, an air pressure test detected a leak along an approximately 40 mm length of the lower plate on the aft side. Sectioning of the coolers revealed that in the failed unit, the cooling channels formed from corrugated sheet metal had not been soldered to the lower plate. The lower plate was attached only at the periphery. Consequently, normal engine oil pressure caused the lower plate to bulge and overloaded the sheet metal sidewalls, resulting in a longitudinal fracture adjacent to the soldered joint.
The previously fitted cooler, which had accumulated 94 hours of service, exhibited two fatigue cracks approximately 25 mm long in the corners of the lower plate sidewall. These cracks had penetrated the full thickness of the chamber sidewall and were characterized by oxidation, indicating stable crack growth.
The manufacturer's data sheet stated that every cooler is pressure checked to 175 psi and periodic samples are burst tested to 350 psi. However, the aircraft owner reported that no documentation accompanied this or any other cooler indicating what checks were conducted prior to release. Given the observed bulge, it seems unlikely that the failed unit could have withstood the 175 psi test, suggesting the test may have been omitted. The USA-based manufacturer could not explain lapses in the manufacturing process, but noted that some coolers had developed leaks due to pressure spikes from certain oil pumps.
Other Information
This type of oil cooler, primarily sold for automotive use, is also used on a number of Jabiru J400/430 aircraft. The owner of G-RCST was aware of concerns among other owners regarding continued use of these coolers. The Light Aircraft Association (LAA), which provides airworthiness services for this aircraft type, planned to conduct a survey of owners to determine the extent of oil cooler problems and evaluate alternative coolers.