What was found
AIRPLANE DID NOT PRESSURIZE ON DEPARTURE. LEVELED OFF EARLY AT 9000' AND COMPLETED PRESSURIZATION FAIL AND UNPRESSURIZED FLIGHT CHECKLIST. FLEW UNPRESSURIZED WITH NO FURTHER ISSUES. NO CAUTION OR ADVISORY LIGHTS ASSOCIATED. REMOVED FROM SERVICE. INSPECTED DOOR SEALS, NO DEFECTS. AFT CARGO BLOW OUT PANEL INTACT. NO CDS FAULTS. PRESSURIZED AIRCRAFT IAW AMM 21-00-00-863-801. PRESSURIZATION NORMAL. DE-PRESSURIZED IAW AMM 21-00-00-863-802. NO DEFECTS NOTED AT THIS TIME. RETURNED TO SERVICE.