TRACON Instructor and Trainee reported the Trainee issued an altitude to an aircraft which resulted in the aircraft flying below the Minimum Vectoring Altitude.
Synopsis
TRACON Instructor and Trainee reported the Trainee issued an altitude to an aircraft which resulted in the aircraft flying below the Minimum Vectoring Altitude.
Narrative
I was providing OJT. Aircraft X was inbound to ZZZ Runway XX from the west about 40 miles out. They had to deviate some around an area of precipitation and descend out of 11000 ft. The Trainee descended Aircraft X to 3000 ft.; but I thought they were assigned 4000 ft. I did not catch that assignment. I was biased that the Trainee would stop the aircraft at 4000 ft. because we had just been discussing why going below that is a bad practice after the Trainee had done a similar thing two times earlier in the same training session. There is an MVA of 3500 ft. from approximately ZZZ 270 radial to 020 radial. I noticed the loss with the aircraft approximately 2 miles inside the 3500 ft. MVA at an altitude of 3000 ft. after the Trainee issued a heading for Visual Approach and I rescanned the data block. I immediately issued a climb to 3500 ft.; but I should have also issued a low altitude alert along with the climb. Aircraft X began climbing and reported the airport in sight at approximately 3400 ft. and the Trainee cleared them for the Visual Approach and switched them to ZZZ Tower. I did not notice the continued descent earlier because I was focusing on getting the Trainee to work around thunderstorms.OJTIs should ensure that they understand what instructions the Trainee has issued and are not biased by their expectations. Controllers should not issue altitudes below an approaching MVA even if it meets the current MVA. At the local facility Controllers should not issue any ZZZ Runway XX arrivals an altitude below 3500 ft. without extenuating circumstances.
Second reporter narrative
Training on West Radar. Aircraft X was an IFR arrival inbound at 10;000 ft. to ZZZ from the southwest. I think I initially descended Aircraft X to 5000/4000 ft. and gave him a northbound vector to avoid convective weather. At some point I descended Aircraft X down to 3000 ft. I then gave Aircraft X a 080 heading towards ZZZ for the visual XX at which point my OJTI keyed up and climbed him to 3500 ft. At the time of my turn; Aircraft X was just shy of two miles into a 3500 ft. MVA. A breakdown in scan and more importantly bad practice on my part resulted in this. I really didn't intend to take Aircraft X as far north as I did. But because of the breakdown in scan and work speed; he entered the 3500 ft. MVA at 3000 ft.Being more vigilant of MVA's but specifically; aircraft arriving into ZZZ from the west side of the airport; landing Runway XX; should always be stopped at 4000 ft. (SW arrivals); and 5000 ft. (NW arrivals; 4200 ft. MVA). Too many MVA's W/NW of ZZZ at 3500 ft. and above. Descending aircraft down to 3000 ft. isn't beneficial; and only requires further attention. Even a small breakdown in scan; or getting behind; can put aircraft flying longer than intended into those MVA's. Leaving the aircraft at 4000/5000 ft. depending on the arrival direction resolves all MVA conflicts.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.