Date: 202101
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Operator: Other unknown
Operating under: Other unknown
Flight plan: IFR
Mission: Other unknown
Flight phase: Descent
ATC / advisory: TRACON ZZZ
Reporter organization: Government
Reporter function: Approach; Departure
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Communication Breakdown; Fatigue
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Airspace Structure; Environment - Non Weather Related
Primary problem: Environment - Non Weather Related

Narrative: Aircraft X checked on and I instructed him to fly a heading and to descend to 070. He read back 060 and I missed it. A few minutes later I observed him at 060 in a 060 MVA about 1/2 nm from a 064 MVA so I issued a low altitude alert and a climb to 065. The pilot entered the 064 MVA climbing from 061. I asked if he had terrain in sight and he did.The pilot pretty clearly said 060 in the readback; but I think the combination of expectation bias and 'six' starting with 's' like 'seven' was enough for me to miss it. A FLM sitting next to me and monitoring me also missed it.This shift was my quick turn with minimum time between shifts so its possible fatigue had something to do with it; although I felt okay at the time.I'll have to be more vigilant about expectation bias regarding the routine altitudes and associated readbacks I deal with every day.Although I'm not sure that fatigue had anything to do with it; I think 9 hours between shifts is not adequate. On average it seems like 8 hours is the recommended amount of sleep and accounting for the commute to and from work; the time it takes to actually fall asleep in bed; and time to wake up and get ready in the morning; I typically get 6 hours sleep on quick turns.Adding to my fatigue is the fact that we've been on 6 day work weeks since mid-summer. Management's stance is that training 7 days a week is the only way to get out of our staffing crisis; but I 100% believe that the associated overtime is having an impact on our fatigue levels and morale. The national training plan was suspended due to the pandemic but at ZZZ trainees are not allowed to have a staffing day unless they're on overtime; and even then they might still have to train. If we allowed trainees to have one staffing day we'd be able to cut back slightly on overtime; trainees and trainers would be less burnt out; and maybe we'd be able to rest for a full weekend every once in a while. Additionally it would help us to be a bit more protected from the virus - every time we train; people are within 6 feet of each other. The training plan was suspended for this reason; but at ZZZ we exceed the training plan's requirements despite it not being active.Adding to my fatigue is the fact that we've been on 6 day work weeks since mid summer. Management's stance is that training 7 days a week is the only way to get out of our staffing crisis; but I 100% believe that the associated overtime is having an impact on our fatigue levels and morale. The national training plan was suspended due to the pandemic but at ZZZ trainees are not allowed to have a staffing day unless they're on overtime; and even then they might still have to train. If we allowed trainees to have one staffing day we'd be able to cut back slightly on overtime; trainees and trainers would be less burnt out; and maybe we'd be able to rest for a full weekend every once in a while. Additionally it would help us to be a bit more protected from the virus  - every time we train; people are within 6 feet of each other. The training plan was suspended for this reason; but at ZZZ we exceed the training plan's requirements despite it not being active.




Synopsis: TRACON Controller reported missing a readback which resulted in the aircraft being below the Minimum Vectoring Altitude.