Date: 202108
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Flight conditions: IMC
Aircraft: PC-12
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Turbine Engine
Component problem: Malfunctioning
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: ATC had just assigned us a descent from our cruise altitude. While in a shallow descent to the newly assigned altitude we received an 'Engine Fire' CAS along with the 'Fire' voice callout. The PM (PIC) immediately identified and reset the master warning. The PM then begun the QRH actions associated with the CAS message as I PF (SIC) suggested lower. The PIC asked for a diversion to [a nearby alternate] from ATC and also asked for a lower altitude. Upon the diversion request ATC asked for the reason why. At this point both crew members agreed this was an [critical] situation and it was declared over the frequency as a possible engine fire. The Controller then asked if we wanted to stay close to the airport and if we could expedite our descent for the ILS. I as PF began an immediate descent to 2;000 feet MSL at around 3;000 feet per minute at full forward speed. In the meantime the PM was donning their oxygen mask while still following the procedures listed in the QRH. As we were about to level off and intercept the localizer our autopilot failed. At this point I was flying the aircraft and setting up the ILS at the same time. Since the autopilot failed I immediately requested the PM to drop the checklist and finish setting up the ILS as I stabilized the aircraft from its descent. It should also be noted that at the time of level off and autopilot failure the Controller issued their first approach clearance to us. Both of us were too busy to properly read it back with everything going on. Once the localizer was set and we were stable we intercepted the glideslope slightly higher than the minimum altitude for the step down fix. I; as PF; kept the speed up and configured with gear first then flaps. I remained at flaps 15 for the landing as I wanted to approach faster to get on the ground quicker. At about 1;200-1;400 feet MSL the red 'Engine Fire' CAS disappeared with the torque decreased to slow the aircraft. I elected to descend below glideslope when the runway was in sight and within glide so we could land as close to the fire trucks as possible that were sitting on the closest adjacent taxiway to the runway. We stopped using full reverse and braking. While the PF was removing their mask I communicated with Tower asking if fire command saw any visible fire. I believe they were on ground frequency while we were on Tower so the response was never heard. After a few seconds I ordered we evacuate the aircraft since we didn't know what the actual situation was. As I was exiting the aircraft the PM (PIC) followed the remainder of the checklist to secure the aircraft for a possible fire. the evacuation was without issue and the remainder of the day was cancelled with the aircraft grounded. While we couldn't confirm a fire existed the degradation of equipment in the aircraft caused enough alarm to assume something could have been seriously wrong. We elected to not shut the fuel off and stop engine as it was still producing power and the surrounding area was IMC with low ceilings. We elected [our preferred alternate] as it provided immediate fire assistance because of their 121 service along with it was directly in front of us. Continuing the flight over water or any longer was not an option as the situation warranted quick action.


Second narrative: We were enroute when we encountered the Engine Fire event. The Red CAS ENGINE FIRE illuminated and the aural warning said 'FIRE.' We identified the CAS; cleared the message; noted that the Red CAS ENGINE FIRE stayed illuminated and told ATC we needed to divert. The closest field was [a suitable airport]; as we turned towards the field ATC asked our intentions and means for diversion; after quick discussion we agreed we needed to [ask for expedited handling] for the matter at hand. The CAS message came to us as we had descended through 8;000 feet to level off at 5;000 feet per ATC instructions. We had continued our descent and turn towards the field as ATC read us the weather and approach being used. Using our CRM I was running the QRH items and [the Captain] was inputting the ILS into the FMS as we were navigating during the descent. While going through the QRH I was able to put my oxygen mask on and when [the Captain] was going to put his on the autopilot failed and we decided to have him handfly the airplane the rest of the way to the ground and continue without his oxygen mask as we were passing through 3;000 feet and beginning to intercept the localizer for the approach.  The full QRH was completed for an ENGINE FIRE red CAS and we evaluated the engine instruments the entire time while on our descent into the field as the CAS had remained on the entire time. We were also looking at the engine cowling and we had not seen any fire or smoke; but we were planning to get the airplane on the ground first before doing any further inspection or analysis. While handling this we were in full IMC and didn't break out of the clouds until passing through 700 feet on the ILS.  Upon breaking out of the clouds we were short final for the field and saw emergency vehicles were already standing by for us. We landed safely on the runway; signaled to [ground personnel] we were shutting down the engine on the runway; and then proceeded to evacuate the aircraft. From the first indication of the CAS message to shutting the engine down on the runway was approximately 6 minutes. After shutting down and evacuating the aircraft the fire and EMS teams rushed to make sure we were OK before proceeding to inspect the aircraft. Upon inspection and walk around with the fire crew there was no indication to us on the exterior of the aircraft that we had been on fire at any time. After completing our services with local airport authority; we had the aircraft towed back to the FBO and put in the hangar while I proceeded to talk to [Company] to let them know of our [situation] and the next steps we were doing moving forward to handle the situation. Upon reflection; I wouldn't have changed anything we had done. We deviated from items on the QRH in order to enhance our safety. The last QRH item told us to feather the engine however; while we were in IMC; we would rather use a fully operable engine to get us as close to the field as necessary before shutting it down. [The Captain] and myself had excellent CRM and delegated appropriate tasks accordingly to make sure we got the airplane and ourselves on the ground safely.


Synopsis: PC-12 flight crew reported diverting to an alternate airport after experiencing an engine fire warning.