Date: 201809
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Marginal
Light: Daylight
Aircraft: PC-12
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class D ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Elevator Trim System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Commercial
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We departed out of ZZZ with a [Part] 135 flight carrying two passengers. We were cleared to take off of Runway XX; assigned runway heading to 2000 feet. Just as I (Pilot Flying) was leveling at 2000 [feet]; the aural warning for 'pitch trim runaway' sounded; with a red CAS message confirming. I instructed my Pilot Monitoring to hit the trim interrupt switch as I controlled the plane and brought back the power. At this point; the trim was about 2/3 nose down. I told Pilot Monitoring to instruct ATC that we would need vectors back to ZZZ and that we were not declaring an emergency; but had a mechanical malfunction. We were asked if we wanted Runway XY; as it was closer; but I said no; as there would be a tailwind. We were instructed to expect vectors for Runway XZ; with hopes of a visual. Pilot Monitoring then asked for the QRH; and once I got the plane more stabilized; I asked if he would be comfortable taking the flight controls so I could run the QRH. I slowed down in order to reduce control forces; and then handed over flight controls; with positive exchange of both those and radios. I read through the QRH once; and then started the actual physical checklist. I can't say for sure; but I believe during the portion of the QRH (step 3) when trim interrupt is set back to normal; the rest of the trim ran away (aural warning and CAS again) before I was able to repress interrupt (pitch trim CB [circuit breaker] pulled; alternate pitch trim CB in). The plane was now fully trimmed nose down. At the end of the checklist; we had another positive exchange of flight controls; and to slow us down even more I opted for flaps 30 and gear down. We got vectors for the RNAV XZ; as the visibility and ceiling were not conducive for a visual at that end of the runway. The wind was 170 at around 10 knots; and gusting around 20 (I considered flaps 40 but decided not to for the wind). We picked up the runway about 4 miles out and followed the LPV to land. After landing; we were asked if we needed further assistance; which we declined. Had my reaction time to the second trim interrupt been faster; I might have been able to catch the trim before it was fully nose down. There were no previous indications throughout the week of a trim issue; so it was a surprise to hear the aural warning on climb out; a busy time as it is.




Synopsis: PC12 Captain reported a pitch trim runaway during climb resulted in a return to the departure airport.