Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 26
Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Airspace Structure; Chart Or Publication; Human Factors
I issued an approach clearance to cross a fix at or above 11;000 ft. until established on the localizer; cleared ILS approach. The aircraft went through the localizer and was correcting back to the localizer and began a descent into a 10;900 ft. MVA. I was giving a relief briefing and looking at the checklist. When I looked back at the screen the aircraft was at approximately 10;700 ft. and already correcting back to the localizer and exiting the 10;900 ft. MVA into a 9;000 ft. MVA. No low altitude alert went off and I didn't issue a low altitude alert as it seemed unnecessary leaving the higher MVA and by the time I would have issued it the aircraft would have been in the lower MVA. My recommendation would be for the pilot to have complied with instruction to maintain 11;000 ft. until established on the localizer prior to beginning descent.
TRACON Controller reported an aircraft flew below MVA while correcting back to localizer course.