MLG IN CONTINUOUS CHOP AT FL310 REQUESTED FL280 AND WAS TOLD AT FIRST TO STAND BY; LATER CLEARED TO FL290 WITH TRAFFIC AT FL280 WHICH FLT CREW MISTOOK AS CLRNC TO DESCEND TO FL280; CTLR CORRECTED.

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THE SWBND MLG WAS AT FL310 ENRTE TO ATC VIA HVQ J145 TOC. WHEN SWITCHED TO MY FREQ; THE PLT RPTED ON AT FL310 IN CONSTANT CHOP AND REQUESTING FL280. I TOLD THE PLT TO STAND BY AND COORDINATED WITH APCH CTLR FOR RELEASE. THE FLT WAS CLRED TO FL290. A MINUTE OR SO PASSED AND THE PLT WAS TOLD THAT FL280 WAS RPTING LIGHT CHOP. PLT RESPONDED SAYING; 'WE'LL GIVE IT A TRY.' THERE WAS TFC HEAD ON AT FL280; ALT SEP WAS IN EFFECT. I CALLED TFC 11 O'CLOCK AND 7 MI; EXPECT REQUESTED ALT IN 1-2 MINS. PLT SAID TFC IN SIGHT AND WAS LEVELING AT FL280. I RESPONDED BY SAYING; 'YOU'RE WHAT?' PLT SAID; 'WE'RE LEVELING AT FL280.' I SAID; 'YOUR ASSIGNED ALT WAS FL290.' PLT SAID HE READ BACK FL280 AND THAT THE COPLT CONCURRED. THE PLT CLBED BACK TO FL290 AND SAID NOTHING MORE. THE PLT WASN'T INFORMED THAT A POSSIBLE PLTDEV HAD OCCURRED. HE WAS LATER CLRED TO FL280 AND SWITCHED TO ATL CENTER. IT APPEARS THE PLT HAD FL280 ON HIS MIND. ON TAPE PLAYBACK THE PLT SAID; 'WE'RE OUT OF 310 FOR 290.' I ROGERED HIS XMISSION WHEN INFORMED OF FLT CONDITIONS AT FL280. HIS 'I'LL GIVE IT A TRY;' MEANT TO HIM THAT HE WAS CLRED TO FL280 WHEN HE WASN'T. SUPPLEMENTAL INFO FROM ACN 88104: PASSING THROUGH FL287 IND CENTER STATED; 'YOUR TFC IS AT 10 O'CLOCK AND 7 MI. CLR OF HIM I WILL HAVE LOWER.' WE REPLIED WE HAD THE TFC IN SIGHT AND WERE ABOUT TO LEVEL AT FL280. WE STOPPED THE DSCNT AT FL285 AND BEGAN A SHALLOW CLB; REALIZING THERE WAS SOME DOUBT AS TO WHETHER THE CENTER HAD INTENDED TO CLR US TO FL280. CENTER THEN QUERIED; 'WHAT IS YOUR ALT?' WE SAID WE HAD BOTTOMED OUT AT FL285 AND HE REPLIED THAT WE SHOULD BE AT FL290. THIS WAS THE FIRST MENTION EVER MADE OF FL290. WE CONTINUED THE CLB TO FL290 AND AGAIN INFORMED THE CTLR THAT HE HAD CLRED US TO FL280. NEXT XMISSION FROM CENTER WAS A CLR OF TFC AND DSND TO FL280 CALL. NO OTHER MENTION WAS MADE OF THE SITUATION AND THE FLT PROCEEDED TO ATL UNEVENTFULLY. SUPPLEMENTAL INFO FROM ACN 88148: I STATED WE HAD THE TFC IN SIGHT AND WE WERE DSNDING TO OUR ASSIGNED ALT OF FL280. HE ASKED WHAT OUR ALT WAS. WE IMMEDIATELY LEVELED OFF AT FL285 AND BEGAN A CLB TO FL290. I STATED WE WERE AT FL285 CLBING TO 290. ATC STATED OUR CLRNC WAS TO FL290. I REITERATED THAT WE HAD BEEN CLRED TO FL280. APPROX 2-3 MINS LATER; ATC STATED; 'CLR OF TFC; DSND TO FL280.'