Date: 201703
Local time of day: 1201-1800
Location: JFZ.Airport, VA
Flight conditions: VMC
Aircraft: M-20 Series Undifferentiated or Other Model
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Initial Approach
Airspace: Class D JFZ
ATC / advisory: Center ZID
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Confusion; Communication Breakdown
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Airspace Violation All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Procedure; Chart Or Publication; Airspace Structure; Airport
Primary problem: Aircraft

Narrative: Aircraft X requested to do the Localizer Runway 25 approach. He was doing the full approach. He was in the procedure turn descending to 5900 feet and then reported established on the approach. I cleared him for the approach and over to advisory frequency. I made a few other clearances to other aircraft and when I looked back; the aircraft was heading due south. I asked the pilot in plain language 'what are you doing'? The transmitter has been having some issues. I could see the receiver lighting up; but could not hear the pilot. I tried again and the same thing happened. So I turned off that transmitter and used a different transmitter. The pilot; which luckily was still monitoring the center frequency; came back on and said that they had some equipment issues coming out of the procedure turn and were making a turn back to join the localizer. At this point; I brought up an IAF for the approach on my scope and told the pilot to maintain present heading and to climb to 6400 feet until established on the localizer. The aircraft was right on the boundary of the terrain increasing from 5900 feet to 6400 feet. The aircraft reported established on the localizer right as I was giving a new controller control of the airspace. No further issue that I am aware of at this time. The situation was very confusing because the aircraft reported established. If the aircraft had not been monitoring center frequency still; we would have had no idea why the aircraft was off course; and would have had no way to climb them for the terrain. The pilot was IFR training and that could possibly be the cause of the off course turn. The frequencies not working at the main transmitter or receiver site also made it very frustrating. I was trying to find out what was going on and to help this pilot but I could not hear what they were saying. I don't think anything could have prevented this deviation. It was very unusual. The radio equipment working correctly for the center would have helped though.


Second narrative: [Report narrative contains no additional information.]


Synopsis: A ZID Center controller cleared an aircraft for an approach than noticed it turn off course into higher terrain below their Minimum Vectoring Altitude.