ACR MLG ALTDEV EXCURSION FROM CLRNC ALT. STARTED DSCNT ON STAR BEFORE BEING CLRED BECAUSE HE WANTED TO MAKE 'EXPECT' ALT AND SPD.

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OPERATING UNDER FLT PLAN WHICH INCLUDES VOLLS 1 ARR INTO KBNA. FLT PLAN STATES 'CROSS VOLLS AT 250 KTS AND 11000 FT.' GETTING VERY CLOSE TO TOP OF DSCNT POINT IF WE ARE TO BE CLRED TO MAKE VOLLS INTXN AT 250/11000. ZTL STATES 'CLRED FOR VOLLS 1 ARR; SWITCH TO ZTL (FREQ).' DUE TO HVY COM RADIO TFC; FO WAS DELAYED IN CALLING ZTL ON NEW FREQ. I FELT THAT I HAD TO START DSCNT OR I WOULD NEVER HAVE MADE VOLLS AT 250/11000. (OUR TCASII SHOWED NO TFC BELOW US WITHIN 40 NM.) I BEGAN DSCNT OUT OF FL240. FO FINALLY GOT THROUGH TO ZTL ON NEW FREQ. SHE ASKED WHO CLRED US TO LEAVE FL240; I REPLIED; NO ONE; BUT IF WE ARE TO MAKE VOLLS AT 250/11000; WE HAD TO BEGIN OUR DSCNT; BUT WE WILL GO BACK TO FL240 IF SHE WANTED US TO. SHE SAID TO CONTINUE DSCNT TO CROSS VOLLS AT 250/11000; THEN SAID THAT THERE IS OFTEN MISINTERP BY PLTS AS TO WHEN TO BEGIN DSCNT. I HAVE 2 RECOMMENDATIONS: 1) WHEN COM RADIO TFC IS HVY; CENTER SHOULD INSTRUCT; 'CLRED VOLLS 1 ARR; MAINTAIN FL240; SWITCH TO ZTL (FREQ).' OR 'CLRED VOLLS 1 ARR; CROSS VOLLS AT 11000 FT; 250 KTS; SWITCH TO ZTL (FREQ).' 2) NOTIFY PLTS EARLY ENOUGH SO THAT WE CAN MAKE AIRSPD AND ALT CONSTRAINTS WITHIN THE CAPABILITIES OF OUR ACFT - - AT LEAST BEFORE THE 3 X 1 POINT. FINALLY; THERE WAS NO TFC CONFLICT.