Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 10
Communication Breakdown; Situational Awareness
ATC Issue All Types; Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Human Factors
I had given Aircraft X direct PROVI; then a while later gave him the descend via clearance. I noticed he started down pretty early so I was watching to make sure I didn't lose spacing with the aircraft behind him. He asked about the speeds on the arrival and I told him to use the published speeds. As he got close to 11;000 feet I asked him his airspeed because I was losing spacing. I then noticed that his altitude went to 10;700 (and the lowest they are supposed to descend is 11;000). I told him to climb and maintain 11;000; got the readback; and then told him the bottom altitude he should be descending to between there and KRANN was 11;000. He responded that he got that now. I didn't point him out to Providence Approach because I thought climbing him was more important; and by the time I issued the climb and got the readback he was out of their airspace again. I called Boston Approach to let them know to keep an eye on him; then I switched him. I realize now that I never gave him the descend via clearance again. There is still a lot of confusion for pilots about descend via procedures. I think they still need better training; especially when it comes to speeds. They still ask us about speeds all the time.
Boston Center Controller reported an aircraft descended below the clearance limit which caused an airspace violation.