Fighter
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 6
Situational Awareness; Communication Breakdown
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Human Factors
Aircraft X inbound for an IFR approach then RTB to ZZZ. Aircraft was level at 6;000 then issued a descent to 4;000. The aircraft read back 'out of 6;000 for 4;000'. They descended to roughly 3;000. I; the Controller noticed this as they entered a 4;000 MVA. Controller issued a climb to 4;000 and heading to turn back into a 3;000 MVA. Controller asked if they could maintain their own terrain and obstruction clearance up to 4;000. The aircraft responded the first time with something similar to 'say again'. Controller reissued the instruction and they answered in the affirmative.The aircraft had omitted part of their return clearance and I had to reissue the specific instructions to them. If I had to guess I would say the pilot had low experience in an [type].
Moses Lake TRACON Controller reported an aircraft below the MVA and related issues.