PC-12
Air Traffic Control Fully Certified
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew FLC complied w / Automation / Advisory
Human Factors; Weather
The field was IFR and visibility was 3/4SM and ceiling Overcast at 300 feet. A Pilatus (PC-12) was inbound on the ILS talking to the local controller. I advised the local controller that he was really low a little over six miles out. The local controller issued a low altitude alert and I advised the local controller that the aircraft was continuing to descend (he was a 500 feet about five miles out). The local controller told him to execute the missed approach and start climbing. The PC-12 complied and then advised that they were going to break off and go back to [departure airport]. The local controller told him to continue on the missed approach. We properly coordinated with Portland TRACON and the TRACON controller advised that they had also had trouble with the PC-12 vectoring him inbound and they believed that it was due to lack of pilot experience.
Tower Controller reported raising the awareness of a PC-12's low altitude on the ILS approach. Local controller issued low altitude alert; followed by clearance to execute a missed approach.