What happened
On 19 October 2016, a Piper PA28-161 Warrior II, registration PK-PBH, was conducting a dual flight training exercise at Tunggul Wulung Airport in Cilacap, Indonesia. Shortly after departing runway 31, the aircraft reached an altitude of approximately 300 feet when the instructor pilot noticed the engine RPM decreasing significantly. Despite attempts to advance the throttle, the engine power failed to recover and eventually quit.
The instructor pilot took control of the aircraft and declared a mayday, initiating an emergency descent toward an open area. During the descent, the crew attempted to restart the engine, but the maneuver was unsuccessful. The aircraft subsequently performed a forced landing in a paddy field approximately 1.3 nautical miles from the runway threshold. Both the instructor and student pilots survived the impact and were able to evacuate the aircraft, though the aircraft sustained substantial damage.
The investigation
Investigators examined the aircraft's engine, fuel system, and flight controls, finding no mechanical abnormalities or fuel contamination. Ground run tests revealed that if the fuel selector valve is left in an incorrect position for more than three seconds, the engine will hesitate and eventually fail because it cannot draw sufficient fuel from the carburetor. The tests also showed that a successful restart after such a failure requires at least five attempts to replenish the fuel lines.
The investigation also looked into the crew's recent history and the flight school's procedures. It was discovered that the student pilot had sustained a wrist injury from a sports incident several days prior to the flight but had not reported the injury to the flight school or the instructor. This injury likely hindered the student's ability to properly manipulate the fuel selector valve during the pre-takeoff checklist.
Findings
- The primary cause of the engine failure was the improper selection of the fuel selector valve, which resulted in insufficient fuel delivery during the high-power takeoff phase.
- The student pilot's unreported wrist injury prevented the correct execution of the 'Before Take-off' checklist, specifically the movement of the fuel selector to the right tank.
- The engine restart attempt failed due to insufficient altitude and the limited time available to perform the multiple attempts required to prime the fuel system.
- The flight school's instructor manual lacked specific guidance regarding the instructor's responsibility to verify the student pilot's completion of critical checklist items.
Safety action
Following the investigation, the KNKT issued safety recommendations to the flying school. These include implementing a fitness-for-duty monitoring system that encourages self-reporting of physical injuries before flight, and updating instructor manuals to clearly define the instructor's oversight responsibilities during student-led checklist executions.