What happened
On 12 September 2013, a Cessna 152, registration PK-KFC, was conducting a local training flight near Batam, Indonesia, when the engine experienced a significant power loss. The flight, operated by PT Aviasi Solusi Prima (Flybest Flight Academy), was being piloted by a student pilot with an instructor acting as the non-flying pilot.
During the climb to 1,500 feet, the crew noticed that the engine RPM had dropped to 2,200, failing to reach the expected 2,500 RPM. Shortly after reaching the target altitude, the engine power continued to decay, falling to 2,000 RPM. As the crew attempted to return to Hang Nadim Airport, the engine oil pressure dropped to zero, and the engine ceased running approximately 15 seconds later. The crew performed emergency procedures and, unable to restart the engine, executed an emergency ditching in the shallow sea. Both occupants sustained minor injuries, and the aircraft ended up upside down, floating on the water.
The investigation
The investigation by the KNKT focused on the engine's performance degradation and the recent changes in the flight school's operational procedures. Investigators examined maintenance records, which revealed that the aircraft had been grounded multiple times in the days leading up to the accident due to power loss and engine issues.
Crucially, the inquiry looked into the flight school's decision to switch from Aviation Gasoline (AVGAS) to Motor Gasoline (MOGAS) in June 2013. Internal correspondence from the Chief Flight Instructor highlighted concerns regarding the quality of the MOGAS, noting that the fuel appeared old, had a strange odor, and was associated with frequent spark plug deposits and engine roughness across the fleet. Metallurgical examination of the engine components, including the pistons, provided evidence of damage consistent with high-temperature operation.
Findings
- The engine had been subjected to overheating for several days prior to the accident.
- This overheating was caused by a combination of using a lean fuel mixture at high power settings and the use of low-octane MOGAS, which placed the engine in a heavy detonation zone.
- The transition from AVGAS to MOGAS was implemented as an alteration without following the required regulatory processes under CASR subpart 43.13.
- Management failed to resolve the technical discrepancies and performance issues that emerged following the change in fuel type.