What happened
During normal cruise flight, the left engine of the aircraft experienced a 20% loss of torque. At this time, company maintenance personnel notified the crew of a potential fuel nozzle leak on that engine. Shortly thereafter, the #1 engine fire warning light illuminated and the fire horn activated.
The captain responded by securing the engine and discharging the #1 fire suppression agent. Following the discharge, the warning lights on the fire handle and condition lever extinguished. The aircraft subsequently completed an uneventful single-engine landing, and all passengers deplaned without further incident; there were no injuries.
The investigation
Investigators found evidence of thermal damage in the aft section of the engine, specifically near the lower turbine support case. An examination of the fuel system revealed that 3 of the 144 'O' rings within the 14-nozzle fuel system were either damaged or deteriorated.
Additionally, testing conducted at the engine manufacturer's facility determined that the inside diameter of the copper gasket used at the fuel drain nipple was 30% to 40% larger than the required specification. This discrepancy caused a misalignment that led to a leak at the fitting.