What happened
On September 8, 2016, a student pilot was conducting a solo VFR training flight as part of an integrated ATPL(A) program. The flight's departure from EPRJ had been delayed by approximately four hours due to morning fog and anticipated poor weather conditions in the Bieszczady region.
While cruising at 3,200 ft AMSL, the pilot began a descent to 2,000 ft AMSL after passing Pisarowce, approaching the Krosno ATZ point "India." Due to weather forecasts indicating high humidity, the pilot activated the carburetor heat. Upon completing the descent and approaching runway 29 at EPKR, the pilot deactivated the carburetor heat.
During the landing roll, as the pilot configured the aircraft for takeoff by setting the flaps and throttle to the takeoff position, the engine RPM began to increase unexpectedly, reaching a maximum of 2,000 RPM despite the throttle being fully open. The pilot immediately aborted the takeoff attempt and moved the throttle to the idle position, at which point the engine shut down during the remaining rollout. After several minutes, the pilot managed to restart the engine and requested to taxi to the hangar area to perform a ground engine test.
The investigation
The investigation focused on the engine's behavior during the landing roll and the subsequent inability to restart the engine with an instructor present. While a mechanic from the Rzeszów flight school was able to successfully restart the aircraft and perform a ground test without further issues, a technical inspection at the home base revealed issues within the ignition system. Maintenance crews replaced the left and right magneto breaker points and cleaned the spark plugs, after which the engine operated normally.
Findings
- The primary cause of the incident was carburetor icing occurring during the descent to the airport.
- High atmospheric humidity levels significantly increased the risk of ice formation in the carburetor.
- The engine's unexpected RPM surge and subsequent shutdown were consistent with the effects of icing and subsequent mechanical fluctuations in the ignition system.