Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Confusion; Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Environment - Non Weather Related; ATC Equipment / Nav Facility / Buildings; Procedure
Current position was approximately 15 NM northwest of CHA; weather conditions were VMC. After a handoff from ATL Center (133.6) to a different frequency (121.7) than the expected TYS Approach Control frequency; 123.9 stored in the Com 1 selector; we were issued a descent to 5;000 FT and a heading of 180 degrees. After a brief period on this heading I questioned our current vector toward higher terrain to the south; but we heard a blend of static along what sounded like Ground Control instructions at another airport. I was questioning if we were still on the correct frequency and we switched from the Company frequency on Com 2 and continued to monitor; while I switched back to ATL on 133.6 to advise that we needed a different vector but was told to return to approach on 121.7. After another attempt to call the Approach Controller we were informed that she had been trying to talk to us on 121.7 and Guard frequency. We were issued an immediate climb to 7;000 and a right turn back to 270 degree heading. This transmission was readable; but weak with static and intermittent bleed over from another frequency. After a subsequent approach clearance a normal approach and landing terminated the flight. We were in compliance with all clearances that were audible to us. The TYS Tower Supervisor informed me during our telephone conversation that there were problems with existing frequencies and that our flight traversed an area that was below his designated MVA. During the subsequent departure back to ZZZ 40 minutes later; the TYS Tower was advising pilots that they were experiencing problems with several frequencies. Unable to hear Approach instructions clearly at all times due to static and bleed over. Using an Approach frequency not in the airport chart and hearing Ground Control instructions and static on the frequency issued (121.7) was confusing. Refrain from using a regional Ground frequency to replace Approach Control.
An Air Carrier pilot reported TYS Approach Control Frequency 121.7 15 NM northwest of CHA has interference from a Ground Control frequency which caused him to miss an Approach Control vector away from high terrain.