Embraer-Empresa Brasileira De Aeronautica EMB-110P1, VH-UQD

During descent into Cairns, the pilot of the Embraer EMB-110
observed the right engine fire warning annunciator illuminate. The
pilot then conducted the quick reference handbook `fire during
flight phase' checks, which included shutting down the right
engine. During these checks the fire warning annunciator
extinguished, and as there was no visual indication of fire or
smoke, the pilot elected not to discharge the engine fire bottle.
The quick reference handbook allows for an 8-second wait after the
engine is shut down. If the fire warning persists then the fire
extinguisher should be discharged. The pilot advised Air Traffic
Control and the aircraft passengers of the engine shutdown. An
uneventful single engine approach and landing was successfully
completed.

The engine fire detection system consists of two independent
circuits for each engine. The sensors are located in the hot
section, accessories section and the generator cooling air
discharge, and are connected to a control box. When a fire or
overheat condition is detected a fire warning light will illuminate
in the T handle for the affected engine, the master caution light
will illuminate and the fire horn will sound.

Investigation by the operator's maintenance organisation found
that three fire detector sensors had failed, resulting in a false
fire warning. The failed sensors were found to contain moisture.
The operator indicated that the aircraft had operated in rain
shortly before the incident flight.