A B727 CREW STARTS A DSCNT FOR FL240 WHEN CLRED TO TURN TO 240 DEG HDG WHEN 130 MI E OF MEM; TN.

Narrative

APPROX 130 NM E OF MEM AT FL310 ON HOLLY 1 STAR; CTR CALLED AND THE FIRST COUPLE WORDS WERE WEAK. WE UNDERSTOOD ATC TO SAY DSND TO FL240 AND SLOW 20 KTS. THE PNF REPLIED TO ATC; 'LEAVING FL310 FOR FL240 AND SLOWING 20 KTS.' ABOUT 45 SECONDS LATER ATC ASKED US OUR ALT. WE REPLIED PASSING FL300 FOR FL240. ATC SAID THEY WANTED US TO TURN TO 240 DEG HDG AND MAINTAIN FL310. IN RETROSPECT; WE SHOULD HAVE QUESTIONED THE INITIAL RADIO CALL AND ATC SHOULD HAVE CAUGHT OUR ERRED READBACK FOR THE DSCNT. ADDITIONALLY; WE WERE GIVEN THE 240 DEG HDG IN THE SAME VICINITY OF A NORMAL DSCNT TO FL240 (IE; A DIRECT TO FL240 IS USUALLY GIVEN AT THAT POS). SUPPLEMENTAL INFO FROM ACN 481511: THE CAPT WAS TALKING TO CTR AND COPLT WAS FLYING. CAPT ASKED THE COPLT IF CTR SAID TO DSND TO FL240 AND HE SAID 'YES.' SO THE CAPT CALLED BACK; 'XYZ OUT OF FL310 FOR FL240 AND SLOWING 20 KTS.' IN RETROSPECT; THE CAPT SHOULD HAVE QUERIED ATC ON HIS INITIAL RADIO CALL. ADDITIONALLY; ATC SHOULD HAVE CAUGHT OUR READBACK AS BEING IN ERROR UNTIL WE STATED THAT WE WERE DEPARTING FL310 FOR FL240. A LITTLE STATIC ON THE RADIO LED TO A MISUNDERSTANDING.