CREW QUESTIONED BY TFC CTLR ABOUT ALT. CREW BELIEVED THEY WERE AT ASSIGNED ALT. CTLR THOUGHT THEY WERE ASSIGNED ANOTHER. NO TFC CONFLICT. CTLR ACCEPTED FLOWN ALT.

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I WAS ON COMPANY FREQ; WHILE LEVEL AT 10000 FT. AS I RETURNED TO APCH FREQ; I WAS INFORMED BY MY FO THAT WE HAD BEEN CLRED TO 8000 FT. AFTER WE WERE LEVEL AT 8000 FT FOR APPROX 5 MINS; THE APCH CTLR QUERIED OUR ALT. I STATED 'LEVEL 8000 FT.' SHE SAID 'I THOUGHT YOU WERE STILL GIVEN 10000 FT BUT 8000 FT IS OKAY. OBVIOUSLY THERE WAS NO CONFLICT. MY FO BELIEVES WHOLE-HEARTEDLY THAT HE REPEATED 8000 FT BACK TO HER. THE APCH AND LNDG WERE COMPLETED WITHOUT INCIDENT. AS I UNDERSTAND IT; THE FAA IS NOT REQUIRING ATC TO BE RESPONSIBLE FOR INCORRECT READBACKS; YET WE BEAR ALL OF THE BURDEN OF CORRECT HEARING AND READBACKS WITH POSSIBLY VERY UNPLEASANT AND COSTLY CONSEQUENCES. I BELIEVE THAT BOTH FLCS AND ATC SHOULD STILL BE JOINTLY RESPONSIBLE FOR SAFE OPS. SUPPLEMENTAL INFO FROM ACN 441840: CAPT WAS OFF ATC FREQ TALKING WITH COMPANY. WE HAD BEEN LEVEL AT 15000 FT PRIOR TO FURTHER DSCNT. GIVEN INITIAL DSCNT TO 10000 FT. FURTHER INSTRUCTIONS WERE; I BELIEVE; 'TURN R HDG 100 DEGS; DSND TO 8000 FT.' I ACKNOWLEDGED AND CHANGED HEADING AND ALT BUGS AS APPROPRIATE. AT SOME POINT WE WERE DIVERTED TO TURN BACK TO 080 DEGS. AFTER LEVEL AT 8000 FT FOR AT LEAST 2 MINS; APCH CALLED WITH; 'SAY ALT.' WE ANSWERED '8000 FT.' APCH SAID; 'WELL; YOU WERE CLRED TO 10000 FT BUT THAT'S OK; I GUESS.' I SAW TFC AT 10 MI AND AHEAD; VISUALLY AND ON TCASII; NO CONFLICT POTENTIAL AT ALL. I TRULY BELIEVE I READ BACK THE 8000 FT ALT; BUT CAN'T SWEAR TO IT. A POSSIBLE EXPLANATION IS THAT ON OUR FIRST 080 DEG HDG ASSIGNMENT I MISTAKENLY ENTERED 8000 FT. WE HAD BEEN AT 8000 FT FOR AT LEAST 2 MINS. THERE WAS RELATIVELY LITTLE TFC; AND APPARENTLY THIS DISCREPANCY WASN'T NOTICED BY ATC EITHER. THIS WAS ONE OF THE FEW TIMES BOTH PLTS WERE NOT MONITORING ATC. IT IS APPARENT THAT AT VIRTUALLY ANY OTHER TIME SOMETHING LIKE THIS WOULD BE CAUGHT.