Stratotanker 135
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance
ATC Equipment / Nav Facility / Buildings; Aircraft; Human Factors
I was vectoring Aircraft X for a RWY32 ILS Approach into ZZZ from the south. He was too high to intercept the localizer below glideslope so I issued him a vector across the localizer (to the east) for descent. There was a flight of two [military fighters] in trail so I didn't want to use the west side of the localizer. The MVA on the east side of the localizer is 3900 so I issued a descent to 4000 and told him to expect a turn back towards the localizer in a few miles. Approximately 2-3 miles later I issued the turn back to the localizer with no response. I tried multiple times on different transmitters without a response. Aircraft X was now approaching a 5900 MVA and descending through 5500. I keyed up on guard frequency to attempt to issue the turn again which Aircraft X responded to and advised that they could no longer hear me on the original frequency of [VHF]. Aircraft X executed their turn approximately 1 mile away from the 5900 MVA descending through 4500. I instructed Aircraft X to expect vectors on guard or to change to my frequency [UHF] if able. Aircraft X came up on [UHF] and no further communication issues were noted. I could have kept Aircraft X at 6000 until he began his turn back toward the localizer but I wanted to ensure he had enough time for descent to be below the glideslope. I was also running out of airspace and would have needed a point out with [Center]; so I opted to start Aircraft X's descent early. I also probably should have issued a low altitude alert on guard; but wanted to attempt the turn away from the MVA while I still had time.
TRACON Controller reported no response from a military aircraft until using guard frequency. Flight was then switched to UHF and turned before entering a higher MVA.