What was found
DEPARTED RWY, CLIMBING TO 9500 FT CARGO DOOR OPENED. CREW DECLARED AN EMERGENCY & RETURNED, LANDING NORMAL. INSPECTION FOUND CARGO DOOR SUSTAINED DAMAGED DURING EVENT ABOVE. ACFT FERRIED TO MX FOR REPAIRS. MX REPAIRED DAMAGE TO DOOR CAP & SURROUNDING SKIN IAW DER INSTRUCTIONS. OPS/RIGGING CHECK OF DOOR LOCK MECHANISHM REVEALED NO DESCREPANCIES. FOUND CHANNEL CRACKED & REPAIRED. AFTER REPAIR PERFORMED GROUND PRESSURIZATION CHK & FOUND SAT. A REVIEW OF EVENTS PRIOR TO DOOR OPENING REVEALED CHANNEL CRACK COULD HAVE BEEN PRE-EXISTING ALLOWING DOOR TO FLEX UNDER CABIN PRESSURE ENOUGH TO DISENGAGE FROM FORWARD LOCK & DISENGAGE ALL LOCKS. ACFT RTS. [CLOSED]