History of the Flight
On 19 December 2011, a Cessna 172P aircraft registered as PK-WTF was being operated by Wings Flying School on a dual flight training from Cakrabhuwana Airport (WICD), Cirebon, to the Karang Ampel training area under Visual Flight Rules (VFR). On board were one flight instructor and one student pilot. At 1233 LT (0533 UTC), the aircraft departed Cirebon with an intended altitude of 2,000 feet. The student acted as pilot flying and the instructor as pilot monitoring.
At 0536 UTC, the student reported over CA NDB at 1,800 feet, then over Suranenggala at 2,000 feet. At 0545 UTC, the aircraft reached Karang Ampel, and the pilot conducted exercises including climbing turn, steep turn, stall recovery, slow flight descent, and engine failure simulation. During the engine failure exercise, the student performed clearing engine procedures several times. At an altitude of 700 feet, the student executed a go-around and climbed to 1,500 feet for return to Cirebon. During the climb, the pilots observed engine power indicating 1,800 rpm and felt the engine hesitating. The flight instructor took over control and attempted to identify the problem while maintaining altitude.
At 0616 UTC, the aircraft descended to about 500 feet, and the student declared an emergency due to engine failure, intending to force land. The controller acknowledged and alerted rescue services. At 0619 UTC, the instructor performed a forced landing on a coastline area approximately 3 nautical miles north of Suranenggala. The aircraft touched down on muddy terrain and flipped inverted. Both occupants evacuated, and no one was injured.
Damage to Aircraft
The aircraft sustained substantial damage, including wrinkling on the nose and tail sections, and came to rest inverted on the muddy surface.
Investigation Findings
Examination of the engine revealed no abnormalities. However, inspection of the induction system found a rubber piece, measuring 12 cm by 0.8 cm, inside the throttle chamber of the carburetor. This piece was believed to have originated from the flapper valve of the induction box. The detachment of the rubber was presumably due to repeated bending action against the box wall in the "CLOSE" position, causing fatigue. The presence of the rubber in the throttle chamber interrupted the fuel-air mixture supply to the piston chambers, resulting in improper combustion, which the pilots perceived as engine hesitation.
Contributing Factors
The investigation identified the following contributing factors: the detachment of rubber from the flapper valve that fell into the carburetor throttle body; the position of the rubber restricting airflow and fuel mixture during take-off power thrust; and the combination of a go-around from low altitude with inadequate time to recover from the power loss.