A TRACON instructor and their Trainee reported the Trainee issued a descent clearance to an aircraft which placed it below the Minimum Vectoring Altitude.
Synopsis
A TRACON instructor and their Trainee reported the Trainee issued a descent clearance to an aircraft which placed it below the Minimum Vectoring Altitude.
Narrative
I was training on radar east. Three aircraft were being vectored for the ILS XXR. Aircraft Y came on frequency about 50 miles northeast of ZZZ1. Trainee issued 6;000 feet and Aircraft Y was in a 6;600 feet MVA; but Aircraft Y was still high around 14000 ft. Trainee was applying anticipated separation and it seemed like it would work. Once I observed Aircraft Y through 7;000 feet; I told the trainee to stop Aircraft Y at 6;600 feet. Trainee transmitted to maintain 6;600 feet. as the Aircraft Y was at 6;600 feet. The pilot acknowledged; said they were descending through 6;600 feet already and asked if they should climb. The trainee said yes; climb maintain 6;600 feet. We observed Aircraft Y continue descent to 6;200 feet and then start the climb back up.As the OJT Instructor; I should have just keyed up and instructed the aircraft to maintain altitude instead of telling the trainee to do so. I wasted valuable seconds that could have kept them from going through the MVA. I also did not expect the pilot to advise they went through the altitude and then ask if they should climb. My expectation was that they would maintain the altitude or climb to it and again there were valuable seconds lost via transmissions. [I should] utilize 7;000 feet. instead of anticipating for aircraft that far out.
Second reporter narrative
Aircraft Y checked out a bit out of the airspace over a 6;600 feet MVA and working towards a 5;500 feet MVA. I can't recall the exact altitude; but I believe they were well above the MVA (15;000 feet or so). I issued a descent to 6;000 feet expecting a normal rate of descent and projecting they would clear the MVA. Two other aircraft checked in and then it was made aware to me that Aircraft Y was at 6;800 feet descending into the 6;600 feet MVA with about 5 miles left of the MVA before it dropped down. I issued a 6;600 feet altitude to Aircraft Y; but they responded they were below it and asked [if] I wanted them to climb. I issued a climb to 6;600 feet. The lowest I observed Aircraft Y on the radar was 6300 feet; but was informed the Aircraft Z's showed them going to 6;100 feet. I don't have a whole lot of recommendations. The previous facility I worked at had very low MVA's and flat terrain and the only MVA's we had were for antennas or wind turbines. So I just need to adjust to working into a more complex airspace system. I don't think going forward I will use anticipated separation with MVA's until I am a bit more comfortable with the airspace.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.