Premier 1
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 15
Communication Breakdown; Distraction; Situational Awareness
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Airspace Structure; Human Factors
Aircraft X was given a descent to the Minimum Vectoring Altitude of 9;000 feet which he read back correctly. I observed him starting the descent and responded to another aircraft checking onto the frequency. The other aircraft failed check on properly so I had to query the check on information; issue a heading and an altitude to descend to. The other aircraft did not read back altitude or give a complete read back so I was in the process of getting him squared away. I then noticed Aircraft X was exiting the edge of the 9;000 foot Minimum Vectoring Altitude and descending through 8-something. He had obviously descended through the assigned altitude. He was already in the 7;000 foot (next) Minimum Vectoring Altitude so I issued a new altitude to maintain of 7;000 feet which he read back and complied with. [I recommend] proper staffing levels; [and a] standalone Supervisor in the TRACON. Had there been another set of eyes scanning as well this may have been avoided.
TRACON Controller reported they did not notice an aircraft descending below its assigned altitude and below the Minimum Vectoring Altitude.