AN ACR B767 FLC START AN UNAUTH DSCNT FROM THEIR ASSIGNED ALT WHEN THE FO MISHEARD AN 'EXPECT' CLRNC AS AN ACTUAL CLRNC.

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WE WERE AT 4000 FT; RECEIVING VECTORS TO KENNEDY. TFC WAS BEING VECTORED TO THE VISUAL APCH FOR RWY 22L. I WAS ANTICIPATING CLRNC TO A LOWER ALT WHEN I HEARD '(CALL SIGN) CLRED VISUAL APCH RWY 22L.' I MAKE IT A STEADFAST HABIT TO ALWAYS REPEAT ALOUD THE INSTRUCTIONS/CLRNCS I RECEIVE SO I SAID 'CLRED VISUAL.' I SLOWED THE ACFT; DISCONNECTED THE AUTOPLT; CALLED FOR FLAPS 1 DEG; THEN FLAPS 5 DEGS; AND STARTED A GENTLE DSCNT. SHORTLY THEREAFTER; APCH SAID; '(CALL SIGN) WHAT'S YOUR ALT?' THE CAPT QUICKLY ASKED ME 'WHAT ARE YOU DOING?' I REPLIED THAT WE WERE CLRED THE VISUAL AND THE CAPT REPLIED THAT NO; WE WERE TOLD TO 'EXPECT' THE VISUAL. ABOUT THIS TIME; APCH CAME BACK AND SAID; 'CLRED VISUAL APCH RWY 22L.' NO COMMENTS; VERBAL REPRIMANDS; INSTRUCTIONS TO CALL ANYONE; ETC; WERE RECEIVED AND OTHER THAN THE HURT PRIDE OF SOMEONE WHO ATTEMPTS TO MAINTAIN HIGH PROFESSIONAL STANDARDS WITH NO ERRORS; THE REST OF THE APCH AND LNDG WERE UNEVENTFUL. THE CAPT AND I ATTEMPTED TO RECONSTRUCT HOW THIS ALL TRANSPIRED. THERE IS ONE ELEMENT OF WHICH WE ARE STILL UNSURE; WHETHER WE WERE IN FACT CLRED FOR THE APCH OR ONLY TOLD TO 'EXPECT.' I HAVE OFTEN RECEIVED THE SAME CLRNC MORE THAN ONCE AFTER THE CTLR FORGOT HE/SHE HAD ALREADY GIVEN IT. HOWEVER; AND HERE ARE LESSONS LEARNED (OR POSSIBLE CAUSES/CONTRIBUTING FACTORS): FATIGUE -- WE HAD BEEN FLYING FOR OVER 10 HRS RETURNING FROM MOSCOW. I WAS TIRED AND I COULD HAVE HEARD WHAT I WANTED TO HEAR. ANTICIPATING A CLRNC AND HEARING WHAT YOU EXPECT AND NOT WHAT WAS SAID. I WAS ACTUALLY REACHING FOR THE AIRSPD KNOB TO SLOW THE ACFT WHEN THE 'CLRNC' WAS RECEIVED SO I MIGHT HAVE HEARD WHAT I WANTED. FINALLY; AS I SAID EARLIER; I ALWAYS REPEAT THE CLRNC ALOUD. I DO THIS SO AS TO AVOID EXACTLY THIS TYPE OF INCIDENT; HOWEVER; THIS PROC ONLY WORKS IF SOMEONE IS LISTENING. LISTEN TO WHAT YOUR BUDDY SAYS -- WHEN HE REPEATS THE CLRNC.