Incident at Winnipeg, Manitoba

1996-05-15: C-GUPP, a Beech 100 was enroute from Red Lake when the crew noted a fire indicator light had illuminated on the right engine. The crew completed a precautionary shutdown of the engine and continued to land safely at the Winnipeg International Airport. The engine fire warning system on the Beech 100 consists of three photoconductive cells (flame detectors) in each engine nacelle along with associated electronics, indicator lights and test switches. The flame detectors, which are sensitive to infrared light, are positioned in the engine compartments to receive direct and reflected rays, thus viewing the entire compartment with only three cells. Heat level and rate of heat rise are not factors in the sensing method. High humidity levels or stray light rays entering the nacelle may occasionally trigger a false fire warning. Following this occurrence, company maintenance personnel inspected the aircraft and determined that a false fire warning had been triggered. High humidity on the day of the occurrence and a low sun angle may have been factors in the false warning event. The entire warning system was checked, physical components were cleaned, and the photoconductive cells were tested in an attempt to identify which if any of the sensors may have been overly-sensitive.