CFTT INCIDENT WHEN A PA30 CFI STARTS AN UNAUTH DSCNT THAT WOULD HAVE PLACED HIM BELOW ENRTE TERRAIN 30 NM NE OF DEST ARPT OF 1A5; NC.

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I WAS FLYING FROM CHO TO 1A5 AT 12000 FT CRUISE ALT. ZTL (OR APCH; I'M NOT CERTAIN) HAD ME SWITCH TO ASHVILLE APCH. THEY DSNDED ME TO 10000 FT THEN SWITCHED ME BACK TO ATLANTA WHICH THEN HAD ME DSND TO 9000 FT. THE NEXT INSTRUCTION WAS 'PA30; DSND AND MAINTAIN 3000 FT' WHICH I READ BACK THINKING WE MUST BE IN THE VALLEY THAT CONTAINED THE ARPT (1A5) WITH AN ELEVATION OF 2020 FT. UPON DSCNT; I CHKED THE GPS AND IT SEEMED THE ACFT WAS TOO FAR AWAY FOR ME TO DSND THAT LOW. THERE WAS A MOUNTAIN IN FRONT OF ME; PROBABLY BTWN ME AND THE ARPT. ABOUT THE TIME I DECIDED TO CALL ATLANTA AND QUESTION MY CLRNC TO 3000 FT (I WAS AT 8300 FT) ATLANTA CALLED ME AND ASKED IF I WAS DSNDING. I ANSWERED 'AFFIRMATIVE; DSNDING TO 3000 FT.' CTLR ASKED 'WHO TOLD YOU TO DSND.' I ANSWERED; 'THE LAST CTLR; I READ BACK THE CLRNC WITH A QUESTIONING TONE IN MY VOICE.' THE CTLR SAID 'PA30; DO NOT DSND BELOW 7000 FT.' THEN SILENCE. MORE THAN ONCE IT SEEMED THEY HAD TROUBLE HEARING ME AND ASKED ME 'HOW DO YOU READ?' I HEARD THEM CLRLY. SOON I WAS IN THE VALLEY OVER 1A5; CANCELED IFR (I WAS IN CLR AIR) AND LANDED. I DID NOT HEAR ZTL TALKING TO OTHER ACFT SO I DON'T KNOW WHAT CAUSED THIS SIT; PERHAPS CTLR ERROR. IF I HAD ANSWERED FOR ANOTHER ACFT THEN THE CTLR WOULD HAVE CORRECTED ME. PERHAPS THERE WAS RADIO INTERFERENCE AND CTLR DID NOT HEAR ME. STILL; HE SHOULD HAVE CALLED UNTIL I ANSWERED CORRECTLY.