History of the Flight
On 8 August 2011, an ATR 72-212A, registration PK-WFG, operated by PT. Wings Abadi Airlines was conducting a flight from Polonia Airport, Medan, North Sumatera. During the flight, the crew observed a fire warning for the left engine. The flight crew discharged the fire extinguisher and shut down the engine. The aircraft returned to Polonia Airport and landed safely. There were no injuries.
Damage to Aircraft
The engine hot section sustained fire damage. The external area of the hot section showed evidence of fire. The flexible fuel hose was burned with a whitish colour. The Inter-compressor Bleed Valve (IBV) was ruptured.
Personnel Information
The Pilot in Command held an Airline Transport Pilot License and had accumulated total flying hours. The Second in Command held a Commercial Pilot License. Both were qualified for the aircraft type.
Aircraft Information
The aircraft was an ATR 72-212A, serial number not specified in the source, powered by two Pratt & Whitney Canada engines. The aircraft had a valid Certificate of Airworthiness. Maintenance records indicated that the fuel nozzle assembly had been modified per Service Bulletin SB 21705, which introduced an O-ring seal to prevent fuel leakage. The O-ring was part of the fuel nozzle assembly.
Engine Fire Detection System
The aircraft was equipped with an engine fire detection loop and a fire handle on the overhead panel. The crew alerting panel displayed fire warnings.
Tests and Research
Examination at the Pratt & Whitney Canada facility revealed that the origin of the fire was a fuel leak from the fuel nozzle assembly. The leak was caused by a failed O-ring (pre-formed packing) that had broken, allowing fuel to escape. The O-ring failure was attributed to improper installation or damage during assembly.
Analysis
According to the investigation, the fire originated from fuel leaking past a broken O-ring in the fuel nozzle assembly. The leaking fuel ignited on the hot engine components.
Conclusion
The contributing factor was: 1. The origin of fire was initiated by the failure of the O-ring of the fuel nozzle assembly that caused fuel leakage. 2. The flight crew did not properly follow the engine fire procedure.
Safety Actions
PT. Wings Abadi Airlines revised their maintenance procedures to ensure proper installation of the Moeller fingers and ring. Pratt & Whitney Canada updated their service bulletins and tooling. The Directorate General of Civil Aviation (DGCA) issued safety recommendations.
Probable Cause
The fire was caused by a fuel leak from a failed O-ring in the fuel nozzle assembly. The flight crew did not properly execute the engine fire procedure.