Light Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Other / Unknown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Flight Crew FLC complied w / Automation / Advisory
Procedure; Human Factors; Airspace Structure
Aircraft X was inbound from the southeast. He came over at 080 feet. The MVA he was in was 050 feet; however; it was dropping to 045 feet after 5 miles from his position at the time of descent; and 6 miles from that it would drop to 030 feet. I gave Aircraft X a descent to 040 feet in anticipation of him being past the 045 feet MVA by the time he was at 045 feet. He descended faster than anticipated and when he reached 053 feet; I amended his altitude to 045 feet to satisfy the MVA. He read back the altitude correctly and stated that he may go a few hundred feet below while correcting. While the MVA was 045 feet; the aircraft descended to 042 feet; then climbed back to 045 feet. The aircraft was shortly after cleared for a visual approach and landed without problem.
BGM Controller reported assigning a lower altitude resulting in an aircraft descending below the MVA.