LTSS BTWN GA-SMT AND AN ACR ACFT AT 9000 FT SW OF CYN.

Narrative

I WAS PLTING THE OWNER'S SMT ON AN IFR FLT FROM ISLIP; LONG ISLAND (ISP) TO LYNCHBURG; VA (LYH) ON V-16. AT 8000 FT WE HAD ENTERED CLOUDS AND THE PAX WERE BEGINNING TO BECOME UNEASY WITH THE TURB AND RAIN. AROUND CYN VOR I REQUESTED 10000 AS A NEW ALT; BELIEVING THAT THIS WOULD GET US ABOVE THE CLOUD TOPS. MCGUIRE APCH COULD NOT APPROVE HIGHER ON OUR ASSIGNED RTE; SO I ADVISED THE CTLR THAT I WOULD ACCEPT AN ALTERNATE RTING IF HE COULD CLR US FOR HIGHER. A FEW MOMENTS LATER HE CALLED BACK WITH AN AMENDED CLRNC WHICH I READ BACK; NO ALT CHANGE. I WAS THEN HANDED OFF TO ZDC; FROM WHOM I AGAIN REQUESTED HIGHER. THE CTLR SAID THAT THERE WOULD BE A DELAY FOR HIGHER; BUT WHEN I ADVISED HIM THAT ONE OF THE PAX WAS BECOMING QUEASY HE WAS GOOD ENOUGH TO CLR US TO 9000. WITHIN A COUPLE HUNDRED FT OF LEVEL OFF; AN URGENT VOICE DIRECTED US TO 'DSND IMMEDIATELY TO 8000'. ASKING NO QUESTIONS; I BEGAN AN IMMEDIATE DSCNT. THE CTLR SAID THAT OUR ASSIGNED ALT WAS 8000. I REPLIED THAT; NEGATIVE; WE HAD BEEN CLRED UP TO 9000. HE CLAIMED THAT THE CLRNC TO 9000 HAD BEEN REVOKED AFTER IT WAS ISSUED. I DID NOT HEAR THE 9000 FT ALT AMENDED AND I CERTAINLY DID NOT ACKNOWLEDGE THIS NEW ALT ASSIGNMENT. THE ACFT'S OWNER (A RATED PLT) WAS SEATED NEXT TO ME AND WAS MONITORING THE FLT AND OCCASIONALLY HELPING OUT WITH THE RADIO COMS. HE ALSO ONLY HEARD THE CLRNC TO 9000 AND NOT ANY SUBSEQUENT AMENDMENT. ABOUT A MIN LATER; THROUGH A BREAK IN THE CLOUDS; I WAS ABLE TO SEE AN AIRLINER CROSS OUR FLT PATH FROM L TO R AT 9000. WE WERE SUBSEQUENTLY CLRED TO 10000 WHERE WE BROKE OUT ON TOP AND CONTINUED TO THE DEST WITHOUT FURTHER INCIDENT. I DON'T BELIEVE THAT THERE IS ANYTHING I COULD HAVE DONE TO PREVENT THIS INCIDENT. I WAS ATTENTIVE TO THE RADIOS AND HAD ANOTHER PLT ALSO MONITORING COMS. IT SEEMS UNLIKELY THAT WE WOULD BOTH MISS A CALL. THE CTLR SHOULD HAVE DEMANDED AN ACKNOWLEDGEMENT TO HIS REVOCATION OF A CLRNC I HAD PREVIOUSLY ACCEPTED; I FEEL; IN ANY CASE.