Cessna 210 Centurion / Turbo Centurion 210C; 210D
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2
Communication Breakdown; Confusion; Situational Awareness; Human-Machine Interface
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert
ATC Equipment / Nav Facility / Buildings; Human Factors; Procedure; Airspace Structure
This aircraft was enroute from ZZZ to ZZZ1 on an IFR clearance that was obtained after departing ZZZ VFR. The pilot requested a clearance to ZZZ1 via ZZZ2 direct after climbing to an altitude where we could hear him on the radios over ZZZ. I checked the route which ran directly between a small restricted area and a high terrain box that we are used to dealing with northwest of ZZZ2. I also noticed a terrain box of 8;900 feet; and thought the requested altitude of 9;000 feet and the route of flight was safe. I failed to observe a smaller terrain box which requires a safe altitude of 10;000 feet. When the Minimum Safe Altitude Warning alert went off; the pilot was apparently in a small area of poor radio reception and I was unable to get an acknowledgement from him from either the of the TRANSMITTERS available to me.His position and altitude are generally not a problem from one of the transmitters. I had to switch a commercial aircraft to the low altitude frequency to relay a climb clearance to the pilot; which took an extra minute or two; by which time the aircraft began to transit the 9;900 foot terrain box at 9;000 feet. He climbed to 10;000 feet shortly after and was also able to hear me on the radio a few seconds after the clearance had been relayed by the commercial overflight. Pay more attention to the terrain boxes even if you think after the initial scan that everything looks good.
A Center Controller reported they approved a direct route for an aircraft which placed the aircraft below the Minimum Vectoring Altitude. The reporter had to relay climb instructions through another aircraft due to poor radio reception.