Incident Description
An ATR-72-12 transport airplane was cruising at 5,000 feet MSL when the #2 engine fire warning light illuminated. The crew shut down the #2 engine and actuated the fire extinguishing system. They then executed a single-engine landing, followed by a normal taxi to the ramp and normal passenger debarkation.
Inspection Findings
Post-incident inspection of the Pratt & Whitney 127 series engine revealed that a fuel transfer tube adjacent to the #2 nozzle was misaligned and had 'backed out' of its retaining clip. Fuel streaking and fire damage were evident down the right side of the engine from the #2 nozzle downward along the fuel nozzle ring assembly.
Maintenance Context
The incident occurred 3.4 hours after the fuel nozzles, retaining clips, and transfer tubes were replaced during maintenance on the #2 engine. The engine manufacturer had published several service bulletins addressing the potential for incorrectly installing the retaining clips. These bulletins recommended that existing clips be replaced with stronger lock plates that provide a positive locking mechanism to avoid misalignment during installation.
Regulatory History
The manufacturer issued a Service Bulletin in October 1994. Transport Canada issued an Airworthiness Directive (AD) in November 1996, both citing how the retaining clips could be installed 'out of position' and recommending that operators use the newer lock plate. The U.S. Federal Aviation Administration (FAA) published a Notice of Proposed Rulemaking (NPRM) on July 17, 1995, addressing the same issues. FAA AD 98-14-02 was published in the Federal Register on July 1, 1998, and was similar to the Canadian AD issued on November 19, 1996.