What was found
KFLL/KGPT - FLT KYC630 - AIR TURN BACK. AIRCRAFT WOULD NOT HOLD CABIN PRESSURE, ISOLATED ALL SYSTEMS. RETURNED TO KFLL. UPON MAINTENANCE INSPECTION, FOUND DEBRIS IN AFT CARGO DOOR SILL, AND DOOR NOT LOCKED CLOSE. DOOR SWITCH STUCK CLOSED. INSPECTED DOOR AND FRAME, OPS CHECK OKAY. PLACED AFT CARGO DOOR WARNING ON DMI 3-2, PER MEL 52-4. RETURNED AIRCRAFT TO SERVICE. (X)