As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 990 - AIRCRAFT UNABLE TO PRESSURIZE IN AUTO OR NORMAL AFTER TAKEOFF. AIRCRAFT RETURNED TO MIAMI WITHOUT INCIDENT OR EMERGENCY. TROUBLESHOT AIRCRAFT PRESSURIZATION SYSTEM AND FOUND GROUND A/C CHECK VALVE LOOSE AND STUCK OPEN FROM GROUND A/C ON ORIGINAL DEPARTURE FLIGHT. RESECURED AND LUBRICATED GROUND A/C CHECK VALVE. OPS CHECKED OK. AIRCRAFT RETURNED TO SERVICE. (M)