FLC MISINTERPRETED CLRNC AND DEVIATED FROM ASSIGNED ALT.

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ZID GAVE US A DSCNT FROM FL370 TO FL300 (THAT'S WHAT WE READ BACK) THEN A FREQ CHANGE. NEXT CTLR WAS VERY BUSY; I RPTED OUT OF FL335 FOR FL300. AT FL322 THEY CALLED BACK AND SAID; WE WERE ONLY CLRED TO FL330. CTLR GAVE US A TURN TO L 180 DEGS AND ASKED US TO SAY ALT. WE WERE AT FL330. CTLR SAID WE HAVE TFC AT 7 MI AND 2000 FT BELOW US; AND TOLD US TO GO ON COURSE. (NO TA'S OR RA'S) WE FEEL WE HAVE A BIG GAP IN OUR 'CRM.' WE JUST CAME FROM A VERY BUSY ARPT AROUND NEW YORK. ONCE WE GOT INTO A FAMILIAR AREA WE GOT COMPLACENT. BOTH OF US MISSED THAT FL300 WAS WRONG. SUPPLEMENTAL INFO FROM ACN 492137: WE ALWAYS HAVE THE PNF WORK THE RADIOS. THE PF ALWAYS SETS THE HEADING BUG AND VERIFIES INPUTS TO THE FMS; HOWEVER; THE PNF IS THE SOLE MANIPULATOR OF THE ALT SELECTOR KNOB. THIS FACT POINTS OUT THAT IF THE PNF MAKES AN ERROR IN SELECTION; THE PF MAY NOT CATCH IT. CHK AND BAL IS GONE. ALSO; FOR THIS PARTICULAR CASE IT SHOULD HAVE BEEN OBVIOUS TO US THAT AN ERROR ON OUR PART WAS MADE (BECAUSE OF THE FACT THAT FL300 IS NOT USED).