FLC OF A SCHEDULED CARGO TWIN TURBOPROP DSNDED FROM ASSIGNED ALT BEFORE CANCELING HIS IFR FLT PLAN.

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I FILED AN IFR FLT PLAN FROM FREEPORT (MYGF) TO MARSH HARBOR (MYAM) VIA BR70V. COMMUNICATING WITH ZMA; I REALIZED THERE WERE 4 IFR ACFT INBOUND AND ARRIVING MARSH HARBOR AT THE SAME ETA. I WAS TO MAINTAIN 7000 FT. I WANTED TO STAY AT 7000 FT AND LET THE OTHER ACFT DSND AND GO AHEAD OF ME INTO MARSH HARBOR. I WAS ALSO LISTENING IN ON MARSH HARBOR UNICOM TO FIND OUT WHERE THE OTHER ACFT WERE WHEN THEY STARTED NOT TALKING TO MIAMI AND TALKING ON UNICOM 122.8. ABOUT 10 MI W OF MARSH HARBOR; I WAS STILL AT 7000 FT; SO I COULD STAY IN RADAR CONTACT WITH ZMA. ZMA ADVISED ME THAT 'RADAR SVC IS INTERMITTENT;' AND 'RADAR CONTACT LOST.' I BELIEVE WITH THE AMOUNT OF TFC GOING IN AT ONE TIME WHICH INVOLVED AN AS-125; BE1900; AND AN AZTEC; WHEN I HEARD 'RADAR CONTACT LOST' I MISTAKENLY THOUGHT MIAMI HAD SAID SOMETHING I USUALLY HEAR WHEN I CANCEL IFR OUT IN THIS AREA DAILY; WHICH IS 'RADAR SVC TERMINATED; FREQ CHANGE APPROVED.' I STARTED DSNDING OUT OF 7000 FT AND REALIZED WHAT I DID WRONG AT 5500 FT. I TRIED TO CANCEL THE IFR BUT WAS TOO LOW TO COMMUNICATE WITH MIAMI. I CANCELED THE IFR FLT PLAN THROUGH A RELAY WITH ANOTHER ACFT. I AM TOTALLY RESPONSIBLE FOR THIS AND DEEPLY REGRET WHAT I DID. I KNOW THIS IS AN INAPPROPRIATE PROC AND AM DEEPLY EMBARRASSED. I STARTED THE DSCNT THINKING I HAD ALREADY CANCELED; AND I WAS COMMUNICATING TO THE OTHER INBOUND ACFT WHICH WERE ALREADY IN THE TFC PATTERN BELOW AND AT LOWER ALTS. I CALLED ZMA UP IMMEDIATELY AFTER LNDG AND SPOKE TO THE BOSS OF THAT AREA.