B757 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3
Human-Machine Interface; Distraction; Situational Awareness; Time Pressure
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Separated Traffic; Flight Crew Returned To Clearance
Human Factors; Procedure
Aircraft X was descending via the STOCR arrival; south transition; near POORE intersection when I noticed him leave 9000 feet. I immediately took action as he went through 8800 feet; issuing a climb back to 9000. The pilot seemed surprised and said something to the effect of 'Yes; we will have to climb back up to 9000'. At which point I issued an immediate westbound turn to avoid a CLT departure climbing to the southeast. Once I was west of the CLT departure; which I believe was an [airliner]; I cannot recall; I put Aircraft X back on course to the downwind leg. This was a close call; had I not noticed this pilot deviation as it was happening; it could have been a far worse outcome. The pilot stated on the phone he accidentally deleted the 9000 box from the FMS.I will also add that on initial check-on; Aircraft X stated they were on the STOCR1 descending to 7000. This is not an uncommon check on. The STAR's bottom altitude is 7000 and that is; in fact; where they are descending to. I should have pried the whole and correct phraseology from him; but at the time I was busy. The fact that the bottom altitude on these arrivals is below the altitude at which CLT departures are climbing is wildly dangerous. This isn't the first instance this has happened. After the first one it should have been changed but it wasn't; so here we go again. Long side arrivals bottom altitude should be 9000. This way; if the FMS drops an altitude; or fix; the clearance limit is at least 9000; not 7000; which is 1000 feet below the altitude of CLT departures!
Charlotte Approach Controller reported stopping an aircraft's descent to prevent a loss of separation with another aircraft. Controller stated pilot accidentally deleted altitude from the FMS.