Narrative:

Over skebr intersection on skebr arrival to las at 12000 ft, first officer flying, we received clearance from approach to 'descend via skebr one except cross ipumy at one-one thousand.' at least that is what we heard and read back. We descended to 11000 ft and after impuny began a descent to 8000 ft as depicted on the arrival. Approach asked us why we were descending as we were supposed to maintain 11000 ft. We stopped our descent at about 10500 ft and were cleared to 9000 ft. We never heard the word 'maintain' in our clearance and we were absolutely convinced we were proceeding properly. If the controller wanted us to maintain an altitude he should not have told us to 'descend via...' when 'maintain 11000 ft' would have been perfectly clear.

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Original NASA ASRS Text

Title: AN MD80 CREW, DSNDING INTO LAS, MISINTERPRETED ATC'S CLRNC, STARTING A DSCNT TO 8000 FT WHEN ATC ALLEGES 11000 FT WAS TO BE MAINTAINED.

Narrative: OVER SKEBR INTXN ON SKEBR ARR TO LAS AT 12000 FT, FO FLYING, WE RECEIVED CLRNC FROM APCH TO 'DSND VIA SKEBR ONE EXCEPT CROSS IPUMY AT ONE-ONE THOUSAND.' AT LEAST THAT IS WHAT WE HEARD AND READ BACK. WE DSNDED TO 11000 FT AND AFTER IMPUNY BEGAN A DSCNT TO 8000 FT AS DEPICTED ON THE ARR. APCH ASKED US WHY WE WERE DSNDING AS WE WERE SUPPOSED TO MAINTAIN 11000 FT. WE STOPPED OUR DSCNT AT ABOUT 10500 FT AND WERE CLRED TO 9000 FT. WE NEVER HEARD THE WORD 'MAINTAIN' IN OUR CLRNC AND WE WERE ABSOLUTELY CONVINCED WE WERE PROCEEDING PROPERLY. IF THE CTLR WANTED US TO MAINTAIN AN ALT HE SHOULD NOT HAVE TOLD US TO 'DSND VIA...' WHEN 'MAINTAIN 11000 FT' WOULD HAVE BEEN PERFECTLY CLR.

Data retrieved from NASA's ASRS site as of July 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.