What happened
On 20 June 2016, a Cessna 172P aircraft, registration PK-NIV, was conducting a routine flight training exercise near the Wedung area in Demak, Central Java. The flight, operated by Nusa Flying School, departed from Ahmad Yani International Airport with two student pilots on board. The flight proceeded without incident for approximately 55 minutes until the aircraft was instructed to hold at 1,000 feet altitude.
During the holding pattern, the pilot observed a loss of engine power, characterized by increased vibrations and a decrease in propeller rotation. In an attempt to troubleshoot the issue, the crew checked the ignition, mixture, and fuel systems. However, the engine could not be restarted. The pilot subsequently executed an emergency landing, guiding the aircraft into a fishpond. While both student pilots evacuated the wreckage with minor injuries, the aircraft sustained substantial damage, and the surrounding water was contaminated by spilled fuel.
The investigation
The investigation conducted by the KNKT focused on the mechanical state of the engine and the operational procedures followed by the crew. Technical examinations of the Lycoming engine revealed no internal mechanical failures or abnormalities in the fuel-air mixture. While investigators found evidence of corrosion and sand deposits on the magnetos and cylinders, these were attributed to the aircraft being submerged in the fishpond following the impact.
A critical component of the inquiry involved the fuel system. Investigators examined the position of the fuel selector valve and the crew's understanding of its operation. The investigation also included a chemical analysis of the fuel, which revealed that the octane number (RON) of the fuel used was below the minimum requirements for the engine type.
Findings
- The primary cause of the engine failure was improper fuel flow resulting from the fuel selector valve being left in an intermediate position between the 'BOTH' and 'RIGHT' settings.
- The crew possessed a flawed understanding of the fuel system; the student pilots believed the intermediate position was a standard setting used to balance fuel between the wing tanks.
- During the troubleshooting process, the crew failed to return the fuel selector to the correct position, which prevented the engine from restarting.
- The fuel used during the flight did not meet the required octane specifications for the engine.