Bombardier Learjet Undifferentiated or Other Model
Air Traffic Control Fully Certified
Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert
Human Factors
I vectored a Lear Jet off the arrival to the ZZZZZ intersection on the RWY XX localizer at ZZZ; with a descent clearance to 3000.  The aircraft's flight path would take him over an MVA of 3000; that was the reason for the altitude assignment.  I observed the aircraft  about a mile west of the MVA between 3100-3000 and it appeared to be leveling.  The next time I noticed his altitude he was over the MVA through 2200.  I issue the low altitude alert and an immediate climb.  The aircraft climbed back to 3000 without incident.  He stated that I cleared him to descend to 2000 and read it back that way.  I thought I clearly assigned him 3000. I should have checked his altitude sooner to verify he did stop at 3000.
APPROACH CONTROL HAD VECTORED US OFF THE [STAR] ARRIVAL AND WERE TOLD TO EXPECT RWY XX AT ZZZ. CONDITIONS WERE VFR AND WE WERE TOLD TO PROCEED DIRECT TO ZZZZZ ON THE ILS XX APPROACH. WEST OF [THE AIRPORT] ARE SOME ANTENNAS THAT EXTEND TO A HEIGHT OVER 2000 FEET MSL.  WHILE PROCEEDING VFR TO ZZZZZ WE HEARD THE CONTROLLER SAY MAINTAIN 2000.  PART OF THE PROBLEM IN THE COCKPIT WAS THAT MYSELF; THE CAPTAIN; DID NOT HAVE MY HEADSET FOR THIS FERRY FLIGHT.  I WAS USING THE OVERHEAD SPEAKER AND WAS NOT HEARING ATC INSTRUCTIONS VERY CLEARLY BUT MY FIRST OFFICER (FO) WAS WEARING HIS HEADSET.  UPON HEARING 2000 MY FO READ IT BACK AS MAINTAIN 2000 IN A QUESTIONING TONE. THE CONTROLLER DID NOT RESPOND AND WE BEGAN TO DESCEND WITH THE TOWERS IN FULL VIEW DOWN TO 2000 FEET.UPON REACHING 2000 I ASKED MY FO; HE DID CLEAR US TO 2000?  HE SAID YES.  I STARTED TO STEER WEST OF THE TOWERS AT WHICH TIME WE GOT THE TERRAIN ALERT AND TRACON CALLED WITH A LOW ALTITUDE ALERT AND TOLD US TO CLIMB BACK TO 3000 FEET.  THE REST OF THE APPROACH WAS UNEVENTFUL.  TRACON ASKED US TO CALL THEM AND THE SUPERVISOR APOLOGIZED FOR THE POOR SERVICE THEY HAD PROVIDED. HE EXPLAINED THAT THE CONTROLLER HAD ASKED US TO MAINTAIN 250 KTS NOT 2000 FEET.  WE EXPLAINED THAT WE READ BACK MAINTAIN 2000 FEET WHICH WAS ON THE TAPE.  CLEARLY THERE WAS A BREAKDOWN IN COMMUNICATION AND THE RESULT WAS A TERRAIN ALERT IN VFR CONDITIONS.
TRACON Controller described a loss of separation with terrain when an incorrect read back was missed by ATC.