ATX LTT MADE A TKOF WITH AFT CARGO DOOR OPEN AND LOST A PIECE OF CARGO WHILE FLYING.

Narrative

UPON ARR AT TOLEDO METCALF ARPT; I WAS ADVISED THAT THE CARGO WOULD ARRIVE AT THE ARPT IN 1 HR. IN THAT WE WOULD BE DEPARTING AFTER DARK; I CONDUCTED THE PREFLT WHILE WAITING AND DURING DAYLIGHT. THE CARGO ARRIVED AND GND HANDLERS AND THE CREW LOADED OUR REAR LOADING ACFT. I PROCEEDED INSIDE THE FBO AFTER TELLING THE FO TO PREPARE THE ACFT FOR DEP. I RETURNED TO THE COCKPIT; TAXIED OUT AND DEPARTED VFR; PICKING UP THE CLRNC IN THE AIR. ALL CHKLIST ITEMS WERE COMPLETED FOR START; TAXI; AND TKOF. AFTER BEING AIRBORNE FOR APPROX 30 MINS THE FO TURNED AND ASKED; 'DID YOU SHUT THE CARGO DOOR'? I RESPONDED IN THE NEGATIVE BUT POINTED TO THE FACT THAT WE DID NOT HAVE AN ANNUNCIATOR LIGHT 'DOOR UNSAFE' OR MASTER CAUTION. UPON EXAMINATION WE FOUND THE DOOR WAS OPEN AND WE HAD LOST 1 CARTON (APPROX 50 POUNDS) OF AUTO PARTS -- PLASTIC. THE OPEN DOOR WAS COMPLETELY OBSCURED BY FLOOR TO CEILING CARGO AND THE WARNING LIGHT HAD FAILED; ALTHOUGH IT WOULD LIGHT IN THE TEST MODE. UPON RETURNING TO BASE; WE SQUAWKED THE DOOR LIGHT; MAINT DETERMINED THAT THE SWITCH AT THE DOOR HAD BEEN DAMAGED. A SECOND WALK AROUND PRIOR TO DEP WOULD HAVE PREVENTED THE INCIDENT. SUPPLEMENTAL INFO FROM ACN 189316: THE ACFT IS CERTIFIED FOR FLT WITH THE DOOR OPEN. WE MADE A CALLBACK TO THE DEP ARPT TO MAKE SURE THE RWY WAS CLR. THE BOX WAS NOT FOUND.