Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Situational Awareness; Time Pressure; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Inflight Shutdown; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
All operations were normal until we had an indication of an engine fire warning in flight. During cruise flight at 9000 ft. MSL while flying through light rain; the left T-Handle; indicating a fire; illuminated. At that point my trainee (Pilot Flying) performed the immediate action items per our checklist. The light remained illuminated past 20 seconds. I decided we should [advise ATC] and perform an engine shut down. I [advised] ATC and planned to land at ZZZ. I notified Dispatch of my decision over company radio. My trainee completed the engine shut down under my supervision. Once we were established on [the] ILS Runway XXL at 2000 ft. and 5 miles from the final approach fix; I took controls of the airplane and landed. The reported ceiling was 6000 ft. overcast. We had the airport in sight 5 miles out; at ZZZZZ.  There were no other indications of a fire throughout the event.  I believe rain caused the plane to have a false indication of a fire. The trainee verbally identified the fire handle illumination as I saw it and continued with the engine fire warning in flight memory items and checklist.
[Report narrative contained no additional information.]
A Beechcraft Model 99 flight crew reported a fire indication in the left engine; resulting in an in flight engine shutdown and diversion.