Narrative:

Descending into las, center gave a crossing restriction of 15000' MSL 25 NM south of las. Both my first officer and I understood the crossing restriction to be south of las. Later the controller asked us if we were going to make our crossing restriction of 25 NM south of bld, which we could not do. We came back to the controller and told her we understood our clearance to be south of las instead of bld. She said no problem, and we went on in (we made our crossing restriction of 25 south of las). The reason for this report is because after talking it over with my first officer, neither one of us was 100% sure where our actual crossing restriction should have been, even though there was a chance we read back our original clearance as, 'at 25 south of bld, ' or more likely, '25 south of 15000',' (not mentioning the fix). This is a typical case of: improper (or at least incomplete) radio discipline, not clarifying and following issued clrncs, and poor situational awareness on my part (15000' 25 NM from las is a little high and tight for an medium large transport for landing).

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION, UNDERSHOT ALT CROSSING RESTRICTION DURING DESCENT INTO LAS.

Narrative: DSNDING INTO LAS, CENTER GAVE A XING RESTRICTION OF 15000' MSL 25 NM S OF LAS. BOTH MY F/O AND I UNDERSTOOD THE XING RESTRICTION TO BE S OF LAS. LATER THE CTLR ASKED US IF WE WERE GOING TO MAKE OUR XING RESTRICTION OF 25 NM S OF BLD, WHICH WE COULD NOT DO. WE CAME BACK TO THE CTLR AND TOLD HER WE UNDERSTOOD OUR CLRNC TO BE S OF LAS INSTEAD OF BLD. SHE SAID NO PROB, AND WE WENT ON IN (WE MADE OUR XING RESTRICTION OF 25 S OF LAS). THE REASON FOR THIS RPT IS BECAUSE AFTER TALKING IT OVER WITH MY F/O, NEITHER ONE OF US WAS 100% SURE WHERE OUR ACTUAL XING RESTRICTION SHOULD HAVE BEEN, EVEN THOUGH THERE WAS A CHANCE WE READ BACK OUR ORIGINAL CLRNC AS, 'AT 25 S OF BLD, ' OR MORE LIKELY, '25 S OF 15000',' (NOT MENTIONING THE FIX). THIS IS A TYPICAL CASE OF: IMPROPER (OR AT LEAST INCOMPLETE) RADIO DISCIPLINE, NOT CLARIFYING AND FOLLOWING ISSUED CLRNCS, AND POOR SITUATIONAL AWARENESS ON MY PART (15000' 25 NM FROM LAS IS A LITTLE HIGH AND TIGHT FOR AN MLG FOR LNDG).

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.