PC-12
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7
Workload; Situational Awareness; Communication Breakdown; Training / Qualification
ATC Issue All Types; Deviation / Discrepancy - Procedural Other / Unknown; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Airspace Structure; Aircraft; Human Factors
I was training a trainee on the sector. It was marginal IFR weather and instrument approaches were needed. Aircraft X was in the arrival flow behind Aircraft Y. The trainee was delay vectoring ahead and assigning speeds to try to maintain separation. At 25 miles from the field the Aircraft X was already 4.3 miles behind Aircraft Y (wake turbulence required 4 miles) and he was still delay vectoring ahead. I told the trainee to delay vector Aircraft X because he did not have enough room. The trainee refused to listen and instead slowed Aircraft X to 150 kts; I think. After telling the trainee multiple times to delay vector Aircraft X the trainee continued to issue slower speed assignments. Aircraft X ended up over the initial approach fix at 6;500 feet at 120 kts. The crossing altitude at that fix is 4;000 feet. I told him to break the aircraft out. He then proceeded to clear them for the approach. I immediately told him to break the aircraft out and the trainee did. He issued a descent to 5;100 feet and a left turn heading 180.The pilot made the turn and continued a rapid descent and told us he was working on something. He descended to 4;700 feet. I took over the frequency and issued a low altitude alert. Aircraft X was heading towards a 5100 foot MVA (Minimum Vectoring Altitude). Aircraft X started a climb and entered the 5;100 foot MVA at 4;900 feet. Aircraft X had gear and flaps already down and apparently was struggling with the aircraft to climb after they were given the approach clearance and slowed to such a slow speed. This trainee has a history of completely ignoring instructions. I need to take the sector away from him as soon my first instruction is ignored.
NCT Controller reported that a trainee's failure to follow instructions caused an aircraft to descend below MVA.