What was found
(CAN) ABOUT 200 FT AGL AFTER TAKEOFF MASTER WARNING WENT OFF AND IDENTIFIED THE FAILURE AS A FUSELAGE DOOR WARNING. QRH CHECKLIST COMPLETED. ACFT WAS NOT PRESSURIZING. MAINTENANCE CHECKED THE AFT BAGGAGE DOOR HANDLE, FOUND POPPED OUT. OPS CHECK OF AFT BAGGAGE DOOR AND HANDLE CARRIED OUT IAW AMM 52-31-00 AND CHECKED SERVICEABLE. ACFT REFUELLED AND DEPARTED WITHOUT FURTHER INCIDENT.