What happened
On July 9, 2018, at approximately 16:22, an AFA72 flight operated by Air Jet Flight Training Center, a DA-40NG with registration B-88123, departed Taitung/Fengnyan Airport for Kaohsiung International Airport. The aircraft was conducting an instrument flight training mission with one flight instructor and two student pilots on board.
While descending through 3,000 feet near the Xiaoliuqiu area, the crew noticed significant vibrations, abnormal engine noise, and the smell of burning oil. Shortly after, the Engine Control Unit (ECU) A and B both failed. The crew declared a 'pan-pan' urgency signal and requested radar assistance for landing at Kaohiguang International Airport. As the crew attempted to check oil pressure, the oil pressure dropped to zero, and the engine suffered a total flameout. After being unable to restart the engine via a windmill start, the crew declared a 'mayday' and prepared for an emergency water landing.
The aircraft impacted the sea approximately 12 nautical miles southwest of Kaohsiung International Airport. All 3 occupants successfully evacuated the aircraft and were rescued by emergency personnel. The aircraft was subsequently lost in the sea.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the engine components and maintenance records. The investigation focused on the mechanical failure of the engine, the crew's emergency response, and the adequacy of the operator's safety equipment and procedures. The investigation also looked into the coverage of ADS-B surveillance in the region and the maintenance requirements for the engine's oil injector.
Findings
- The primary cause of the engine failure was pitting corrosion in the engine oil injector, which caused an excessive oil flow. This led to abnormal thermal stress on the number 4 piston crown, resulting in a hole in the piston. The subsequent loss of oil through this hole caused the engine to flame out.
- While the engine maintenance manual required an overhaul every 1,800 hours, there was no specific requirement to inspect the oil injector prior to that interval. However, findings indicated that the injector's performance could degrade after 900 flight hours, increasing the risk of failure.
- The crew's execution of emergency procedures and the water landing process complied with established regulations.
- The investigation noted that the operator's manual included water landing procedures in an appendix but lacked them in the primary emergency response sections, which could impact crew readiness.
- There were also findings regarding the maintenance of life jackets, specifically that battery strength checks for the integrated position lights were not sufficiently addressed in the routine inspection items.