Challenger CL600
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7
Confusion; Communication Breakdown; Situational Awareness; Training / Qualification
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Airspace Structure; Human Factors
I was providing On the Job Instruction during the event. I had previously cleared Aircraft X to 17;000 feet prior to the trainee taking position. Another aircraft; Aircraft Y; was also receiving vectors for the approach and was given a descent to 14000 feet and a speed reduction to 210 knots. Aircraft X read back the instructions and then immediately Aircraft Y read back the instructions. On position; I did not hear the call sign of Aircraft X and thought that Aircraft Y read back the instruction a second time. It was clearly a different voice so I just thought that the pilots were confused as to who was talking and who was flying. A few moments later the Developmental recognized that Aircraft X was at 15;200 feet in a 15;500 foot Minimum Vectoring Altitude (MVA) and issued a low altitude alert. The pilot responded that it was blocked and the trainee gave an immediate climb to 16;000 feet. I recognized the the trainee did not use the full proper phraseology by not saying the 'MVA in your area is XXX;' but decided at this point the solution had been acknowledge and it was not worth correcting the phraseology in a third transmission. The aircraft continued to descend to 14;400 feet until we observed a climb. During that time the aircraft crossed into a 14;900 foot MVA; but being in a climb I decided it was not necessary to issue another safety alert since we knew it was being corrected.There was a bit of frequency congestion due to confusion about the weather; and by the time I was ready to issue a brasher warning the aircraft was on a 10 mile final. I felt it was best to let the aircraft fly and have Local Control or Ground Control issue the brasher warning; so I coordinated that with Ground Control.
A TRACON Controller conducting on the job training reported they did not realize the wrong aircraft read back a descent clearance and the aircraft descended below the Minimum Vectoring Altitude.