What happened
On 1 September 2010, a Cessna 172 Skyhawk, registration PK-ROG, operated by Bali International Flight Academy, was conducting touch-and-go training maneuvers at Blimbingsari Aerodrome in East Java. During the training session, the instructor pilot observed fluctuations in the engine oil temperature. By the fifth maneuver, the temperature had stabilized at the upper limit of the red band.
Following the decision to abort the training and return to the home base at Buleleng, the aircraft began a climb. At an altitude of 500 feet, the engine oil pressure began to drop significantly. Shortly after reaching 700 feet, the engine lost all power. The instructor notified air traffic services of the emergency and executed a forced landing in a nearby rice field. The aircraft came to rest in an upside-down position. While the two student pilots and the instructor evacuated the wreckage, the instructor and one student sustained minor injuries.
The investigation
Investigators examined the wreckage and the engine components to determine the cause of the power loss. The examination of the engine's second cylinder revealed that the coating on the cylinder liner had undergone de-lamination. This defect allowed combustion gases to leak into the crankcase, which subsequently caused the engine temperature to rise and the oil pressure to drop.
Technical analysis of the cylinder liner showed that the de-lamination was likely a result of an improper manufacturing process, specifically involving inadequate surface preparation which left foreign particles on the liner before the coating was applied. This condition was further exacerbated by excessive heat from engine detonation. The investigation also looked into the recent switch from Avgas to mobile gasoline (Mogas) under a Supplemental Type Certificate; however, laboratory tests confirmed the Mogas had an appropriate octane rating and was not a contributing factor to the failure.
Findings
- The engine failure was caused by de-lamination of the coating on the cylinder #2 liner.
- The manufacturing process for the cylinder liner was flawed, leaving impurities that led to coating failure.
- The engine oil temperature and pressure fluctuations were symptoms of the internal leakage caused by the liner defect.
- The use of mobile gasoline was not a factor in the engine's mechanical failure.
Safety action
Following the accident, the Bali International Flight Academy implemented several safety measures, including inspecting the entire fleet for similar cylinder liner issues and temporarily reverting to the use of aviation gasoline. The Directorate General of Civil Aviation also issued safety circulars mandating inspections for specific Lycoming piston engine cylinder assemblies and reviewing procedures for aircraft fuel storage and handling.