PC-12 First Officer reported an engine indication malfunction on a maintenance ferry test flight during descent. The malfunction recovered to normal and the flight made a precautionary landing at an airport and taxied to the ramp.

Narrative

I was scheduled as an SIC (Second in Command) on Aircraft X for a maintenance flight. I did a very thorough preflight inspection because the plane had been in maintenance for an elongated period of time. We boarded and got the airplane started following all checklists and SOPs. We took off VFR and were on flight following with ZZZ Approach while maneuvering; reaching a max altitude of approximately 13500 feet. We began our descent and headed towards ZZZ. At about 7000 feet MSL we got an amber CAS (Crew Alert System) message saying ENGINE ITT. Both PIC and SIC saw ITT (Interstage Turbine Temperature) temps dropping to 110°C. This lasted approx 5 sec. After a momentary recovery to normal the condition returned and remained for approximately 45 seconds. We reached for and ran through the QRH. PIC and SIC discussed the possibility of an engine failure; but were not certain because the other engine instruments were all positive and in the green range. It was determined by both pilots that we should advise ATC and get priority to the airfield given the uncertainty of the condition and the volume of student pilots and traffic at ZZZ. The traffic and congestion in and surrounding ZZZ class D is noteworthy and was very significant in the decision to request priority handling. We landed flaps 15° without incident and taxied back to the FBO; met by emergency crews.