A CARJ CREW RESPONDED TO WHAT THEY THOUGHT WAS A CLRNC TO DSND FROM FL200 TO FL190. THE CREW'S QUERY OF ATC ABOUT SIGHTED TFC; REVEALED THEIR DSCNT TO FL190 WAS IN ERROR.

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ON APR/WED/02; I WAS THE PIC FOR THE FLT OPERATED BY ACR X FROM MHT TO IAD. ABOUT 20 MI S OF THE BWZ VOR; I (PNF) SWITCHED OFF THE MAIN FREQ TO MAKE A PAX ANNOUNCEMENT (REQUIRED BY OUR FLT OPS MANUAL). DURING THE TIME I WAS OFF; MY FO WAS GIVEN A CLRNC TO DSND TO FL200. HE ACKNOWLEDGE THE CTLR AND PROGRAMMED THE AUTOPLT TO FL200. SHORTLY AFTER (ACCORDING TO HIM) HE THOUGHT HE UNDERSTOOD A CLRNC TO FL190. HE SET THE AUTOPLT ACCORDINGLY. WHEN I CAME BACK ON FREQ; HE BRIEFED ME THAT A DSCNT TO FL190 (WHICH WE WRE NEAR LEVELING) WAS ISSUED. A LITTLE BIT OF TIME LATER; I NOTICED AN ACFT APCHING FROM THE E. I QUERIED ATC AND I WAS ASKED MY ALT I ADVISED ATC THAT WE WERE LEVELING AT FL190 AND THAT I HAD NOTED SOME TFC. THERE WERE NO TA/RA ADVISORIES AND NO ACTION TAKEN BY EITHER ACFT. AFTER THE ACFT PASSED; THE CTLR ADVISED ME THAT WE WERE ONLY CLRED TO FL200. I HAD A DISCUSSION WITH THE FO WHO STATED THAT HE UNDERSTOOD THE CLRNC TO BE FL190. NO FURTHER ACTION WAS TAKEN AND SHORTLY WE WERE HANDED OFF TO ANOTHER CTLR. THE FLT CONTINUED TO THE DEST WITHOUT FURTHER INCIDENT. ON THE GND; I MADE NOTIFICATION TO OUR ATC MGR; CHIEF PLT AND THE ATC SUPVR FOR ZNY. I ADVISED THEM OF THE INCIDENT AND ALSO ADVISED THEM THAT WE WERE ABLE TO MAINTAIN VISUAL CONTACT AT ALL TIMES WITH THE ACFT. I FILED THE REQUIRED PAPERWORK.