B757 FLC HAS ALTDEV DURING RNAV ARR.

Narrative

WE EXPERIENCED A PROB WITH AN ATC CLRNC WHILE DSNDING TO OUR DEST OF LAS. WE WERE INITIALLY CLRED BY ZLA TO DSND VIA THE LYNSY 1 RNAV ARR. WHILE DSNDING THROUGH FL220; WE WERE TOLD TO STOP THE DSCNT AT FL190. WHILE LEVEL AT FL190; THE FO WAS OFF THE RADIO; GIVING THE IN-RANGE PA ANNOUNCEMENT TO THE PAX. THE CAPT (PF) WAS GIVEN A CLRNC TO DSND VIA THE LYNSY 1 ARR TO MAINTAIN 10000 FT (VERSUS 8000 FT AT UTARE INTXN). WHEN THE FO CAME BACK INTO THE LOOP; THE CAPT HAD THE SPD BRAKES EXTENDED AND WAS EXPEDITING THE DSCNT; MISTAKENLY THINKING THAT THE CLRNC WAS TO CROSS LYNSY INTXN AT 10000 FT. WHILE PASSING 11000 FT; PRIOR TO LYNSY; ATC ASKED WHAT OUR ALT WAS; AND WE ACKNOWLEDGED PASSING 10900 FT FOR 10000 FT. THE CTLR A FEW MINS LATER ISSUED US A TRACON PHONE NUMBER TO CALL. WE DISCUSSED WHAT HAD HAPPENED WITH THE SUPVR THERE. THE POTENTIAL FOR ERROR EXISTS FOR ALL RNAV ARRS WHEN AN EXCEPTION TO IT IS GIVEN; IE; EXCEPT MAINTAIN 10000 FT VERSUS 8000 FT. IN THIS CASE THE ERROR WAS NOT CAUGHT BY THE PNF; AS HE WAS VERBALLY TOLD BY THE PF WHAT THE CLRNC WAS. A PLT JUMP SEATER HAD INTERPED THE CLRNC TO BE THE SAME AS THE PF HAD; SO THE FO DID NOT VERIFY THE CLRNC AS HE NORMALLY WOULD DO IF IN DOUBT. IN RETROSPECT; I DID NOT REMEMBER EXACTLY HOW I READ BACK THE CLRNC; AS I IMMEDIATELY BUSIED MYSELF FOR THE DSCNT; THINKING I WAS TO CROSS LYNSY AT 10000 FT. THERE WAS NO CONFLICT WITH TFC IN THIS CASE; AND; AFTER OUR CONVERSATION WITH THE TRACON SUPVR; WE DO NOT BELIEVE THERE IS ANY ACTION BEING TAKEN AGAINST US.