What happened
While flying at 5,000 feet MSL, the crew of an ATR-72-12 observed the #2 engine fire warning light illuminate. In response to the alert, the crew shut down the #2 engine and activated the fire extinguishing system. The aircraft subsequently completed a single-engine landing, followed by a normal taxi to the ramp and the standard debarkation of passengers. There were no injuries reported.
The investigation
Post-flight inspection of the P&W 12മുണ്ട 127 series engine revealed that a fuel transfer tube located adjacent to the #2 nozzle had become misaligned and had "backed out" of its retaining clip. Investigators found evidence of fuel streaking and fire damage extending down the right side of the engine, starting from the #2 nozzle and continuing along the fuel nozzle ring assembly.
The incident took place approximately 3.4 hours after maintenance work had been performed on the #2 engine, which included the replacement of the fuel nozzles, retaining clips, and transfer tubes.
Findings
Records indicate that the engine manufacturer had previously issued several service bulletins regarding the risk of incorrect installation of these retaining clips. The manufacturer recommended replacing existing clips with stronger lock plates designed to provide a positive locking mechanism to prevent misalignment.
Regulatory history shows that Transport Canada issued an Airworthiness Directive (AD) in November 1996, and the FAA published a Notice of Proposed Rulemaking in July 1995, both addressing the issue of clips being installed "out of position." Additionally, FAA AD 98-14-02 was published on July 1, 1998, mirroring the Canadian directive.