C207 ENRTE TO FBI VFR AT 3500 FT HEARD LOUD BANG AND NOTED THE REAR CARGO DOOR OPEN. DOOR HIT THE FUSELAGE HARD ENOUGH TO ACTIVATE THE ELT. ABLE TO MAKE COM WITH APCH CTLR AND TWR AND LANDED FBI OK. DAMAGE TO THE DOOR AND FUSELAGE.

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I DEPARTED STEVENS VILLAGE RWY 7 ON THE LAST LEG OF A TRIP FROM FAIRBANKS TO BEAVER; STEVENS AND BACK TO FAIRBANKS. I HAD DEPARTED STEVENS; A 2100 FT ROUGH GRAVEL STRIP (BUMPY). I HAD CLBED TO 3500 FT WITH A LITTLE LIGHT TURB. AFTER LEVELING OFF IN CRUISE FOR APPROX 10 MINS I HEARD A LOUD 'BANG' FOLLOWED BY THE ELT SIGNAL. I LOOKED BACK TO SEE THE REAR CARGO DOOR OF MY C207 HAD SWUNG OPEN AND HIT WITH SUCH FORCE TO SET OFF THE ELT. I QUICKLY ASSESSED MY LOCATION AND DETERMINED THAT PROCEEDING TO FAIRBANKS WAS QUICKER THAN TURNING AROUND AND HEADING BACK TO STEVENS VILLAGE AND LNDG THERE. I PROCEEDED TO FAIRBANKS AND WAS ABLE TO CONTACT A FELLOW PLT ON MY COMPANY FREQ TO RELAY THE INFO TO COMPANY AND NOTIFY FSS OF MY ELT. IT WAS VERY DIFFICULT TO RECEIVE ON MY RADIO DUE TO THE BLARING ELT SIGNAL. IT BLED OVER ALL FREQS. I WAS ABLE TO GET THE ATIS AND THANKS TO THE PATIENCE OF APCH AND TWR GOT A CLRNC TO LAND RWY 1L AT FAIRBANKS INTL. I WAS TRAINED AS TO THE PROPER WAY TO SECURELY CLOSE THAT DOOR; AND ACTED IN THAT FASHION. IT HAD BEEN STRESSED TO ME THE IMPORTANCE OF PROPERLY LATCHING THAT DOOR SO I HAD ADOPTED THE PROC SO I FELT INSURED THAT THE DOOR WAS PROPERLY SECURED EACH TIME IT WAS CLOSED. THE DOOR CAUSED DAMAGE TO ITSELF; AS WELL AS; THE FUSELAGE SKIN AND STRUCTURE FROM INITIAL OBSERVATIONS.