Incident Overview
During the descent phase of a flight operated by a Boeing 727, the flight crew observed the illumination of the fire warning light for the number one engine. In response, they discharged two fire extinguisher bottles into the affected engine. However, the warning light remained illuminated after the discharge.
Emergency Procedures
The crew subsequently declared an emergency and proceeded to land at their intended destination. Upon landing, an emergency evacuation was initiated. During the evacuation, four passengers sustained minor injuries.
Post-Event Examination
A subsequent examination of the aircraft revealed that the 13th stage bleed air duct line leading to the fuel heater was leaking at its input side. The leak was impinging on a fire detection loop located approximately two inches from the leak source.