Small Transport; Low Wing; 2 Turboprop Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 19
Confusion; Human-Machine Interface
Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Human Factors; Procedure
Trainee assigned 2;300 feet to aircraft on vectors for ILS approach.  Upon listening to the tape; it was confirmed that the pilot read back 2;000 feet.  He actually descended to 2;000 feet and was right over the antenna that determines the 2;300 feet MVA for the area when we caught it; but was showing 2;100 feet.  I assumed he was at 2;300 feet and showing low; but he told us that he was at 2;000 feet when he was cleared for the approach and told to maintain 2;300 feet until established.Listen to read backs better.
FAY Approach controller describes seeing an aircraft lower than what they thought they assigned; at an altitude right at the MVA. Controller listened to tapes and pilot read back incorrect altitude; but controller did not catch it.