What happened
On April 16, 2014, a Liberty XL-2 was conducting a night flight approaching Rzeszów-Jasionka airport. Approximately one hour and 20 minutes into the flight, while the crew was executing an ILS approach roughly 7 nautical miles from the threshold of runway 27, the engine began operating unevenly, accompanied by significant vibrations. During this period, a slight loss of power occurred, and the FADEC CAUTION light illuminated, though other engine parameters remained within normal limits. The crew reported the issue to air traffic control without declaring an emergency.
Upon landing and taxiing to the parking stand, a leak was observed coming from the exhaust pipe. This leak was identified as a mixture of fuel, oil, and carbon deposits that had been washed out of the cylinder.
The investigation
Following the incident, an engine inspection was performed the next day. The investigation established that one of the four fuel injectors, specifically on cylinder number 4, was malfunctioning by continuously supplying fuel. This caused fuel to escape through the exhaust valve and the exhaust manifold. After the faulty injector was replaced, the engine returned to normal operation. A Technical Occurrence Report (TORF) was subsequently developed, supported by video evidence from engine tests, which confirmed that the injector had become stuck in the open position. The engine manufacturer was notified of the findings, though they did not provide a specific cause for the injector failure.
Findings
- The primary cause of the engine instability and vibrations was the stuck-open position of the fuel injector on cylinder number 4.
- The malfunction resulted in an improper fuel-air mixture and the subsequent discharge of fuel, oil, and carbon deposits through the exhaust system.