Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 0.5
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Procedure; Human Factors; Chart Or Publication; Airspace Structure
Aircraft X was being vectored for a straight-in Runway 21 approach. I issued a correct clearance to cross BUWME at or above 7;500 ft. The pilot read back 7;000 and the error was not caught by me. These events occurred in an MVA of 7;500 ft. I observed the aircraft descending to 7;200 ft and corrected the aircraft. The lowest altitude observed was 7;000 ft. Once corrected the pilot stated that he could maintain his own terrain and obstruction clearance; which in this case is not applicable. I reissued the correct crossing altitude and clearance; and the aircraft landed without incident. The FLM on duty was working LC/GC/FD/CD/CIC combined at the time due to low traffic volume. He was immediately aware of the situation as it was happening and after the aircraft landed; he was issued a BRASHER warning.Ensure correct read-back of instructions despite traffic volume. I was monitoring the altitude and was able to correct it once the 300 ft variance was no longer a factor; so proper scan will correct it; even if you miss the read-back.
CPR Approach Controller reported an aircraft cleared for an approach descended below the assigned altitude and below the MVA.