What happened
On 30 December 2014, a Roko Aero NG4 UL, registration OK-TUR 22, departed Newcastle Airfield for a private flight with two pilots on board. During the flight, which reached an altitude of approximately 3,000 feet, the pilot noticed blue smoke in the cockpit followed by a rapid drop in engine oil pressure.
Upon recognizing the low oil pressure warning, the pilot took control and prepared for an off-field landing. To protect the engine from potential damage, the pilot shut down the engine at an altitude of roughly 300 feet before touching down in a large, unobstructed field south of Wicklow town. The aircraft sustained no damage and there were no injuries to the crew.
The investigation
The AAIU examination of the aircraft revealed that the engine oil sump was empty. Investigators traced the leak to a flexible hose that supplies oil to the engine oil cooler, which had disconnected from its fitting at the engine oil filter adapter.
Further inspection showed that the other end of the same hose was not fully seated on its fitting at the oil cooler. The investigation also noted that the worm-drive hose clamps used to secure the lines were at the limit of their adjustable range. Testing conducted by the investigators demonstrated that installing such hoses while the fittings or the hose interior are wet with oil can significantly compromise the security of the connection, potentially allowing the hose to rotate and eventually detach under the vibration and pressure of engine operation.
Findings
- The loss of oil pressure was caused by the detachment of a hose supplying oil to the engine oil cooler.
- The disconnection resulted in the total loss of engine oil during flight.
- The hose was secured using worm-drive clamps, which were found to be at their minimum diameter.
- The end of the hose at the oil cooler was not properly seated on its fitting.
- The presence of oil on the fittings during assembly may have contributed to the hose slipping.
Safety action
Following the investigation, the aircraft owner replaced the existing hoses with a more secure screw-on type. The AAIU issued two safety recommendations to the engine manufacturer, Jabiru Aircraft Pty Ltd:
- A requirement to include a warning in maintenance manuals regarding the risks of installing oil cooler hoses when the fittings or hose interiors are wet with oil.
- A recommendation to notify engine users of the details of this specific event to prevent similar occurrences.