A CESSNA 406 IN CRUISE AT 4500 FT HAD THE LOWER CARGO POD FORWARD DOOR DEPART THE ACFT.

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AT APPROX XA50 LCL TIME ON ACR FLT XXX FROM BFI ON RTE TO WXW; UNITED STATES ACFT XYZ EXPERIENCED A COMPONENT FAILURE OF THE CARGO 'BELLY' POD DOOR. DURING A PRIOR FLT IN THIS ACFT; I NOTED THE FORWARD CAM-LOCK LATCH WAS NOT AS FIRM IN THE SECURE AND LOCKED POS AS THE REAR CAM-LOCK LATCH. I PLANNED ON SVC BY A ZZZ MAINT TECHNICIAN ON MY NEXT TRIP THROUGH ZZZ; UNITED STATES; WHERE OUR MAINT FACILITY IS LOCATED AND FLT OPS ARE CENTRALIZED. WHILE IN THE CRUISE PORTION OF THIS FLT; A VIBRATION DEVELOPED AND WAS FOLLOWED APPROX 5-10 SECONDS LATER BY A 'THUMP' FROM THE CARGO BELLY POD DOOR LOCATION AND THE VIBRATION CEASED. AS I COULD NOT VISUALLY VERIFY THE DEP OF THE DOOR DUE TO MY POS IN THE ACFT; I CONTACTED A NEARBY COMPANY ACFT AND REQUESTED A VISUAL INSPECTION OF THE EXTERIOR OF MY ACFT FOR ANY INDICATIONS THAT CONTINUATION OF THE FLT OR AN ATTEMPTED LNDG COULD EXACERBATE THE SIT. AFTER COMMUNICATING ON A DISCRETE FREQ TO COORDINATE THE RENDEZVOUS IT WAS AGREED THAT WE WOULD NOT ENGAGE IN FORMATION FLT AS BOTH ACFT CONTAINED PAX YET PASSING IN A CLOSER PROX OF ABOUT 1/2 MI WAS NECESSARY TO INSURE AN ADEQUATE VISUAL INSPECTION. IN STATEMENTS TO COMPANY MGMNT THE PLT OF THE OTHER ACFT MADE FLIPPANT REMARKS (IN REF TO FAR 91.3(B) DEV AUTH) OF BEING AS CLOSE AS 100 FT APART. I DISAGREE WITH THESE STATEMENTS AND JUDGE OUR DISTANCES DURING BOTH PASSES TO HAVE BEEN NO CLOSER THAN 1/4 NM AND NON-EXISTENCE OF AN EMER. THE EXTERIOR INSPECTION YIELD CONFIRMATION THAT ONLY THE FORWARD PORTION OF THE CARGO BELLY POD DOOR HAD DEPARTED THE ACFT AND NO OTHER INDICATION OF DAMAGE EXISTED. AFTER ASSESSMENT OF THE SIT; PAX DEST AND CONTRACT MAINT AVAILABILITY IN WXW; I CONTACTED COMPANY DISPATCH AND INFORMED THEM I HAD A PROB AND IT WAS MY JUDGEMENT TO CONTINUE THE FLT TO WXW. THE DISPATCHER ON DUTY ACKNOWLEDGED AND MADE NO FURTHER INQUIRY. THE SUBSEQUENT ARR AND LNDG WERE UNEVENTFUL; AN ENTRY WAS MADE IN THE ACFT MAINT LOG AND THE ACFT WAS GNDED FOR NEEDED REPAIRS IN WXW; UNITED STATES.