Narrative:

After fuzzy, cleared to descend via tragr 1 arrival except maintain 8000 ft. We started descent and evidently crossed povoc above 9000 ft. My understanding was that we were to follow speed restrs but vertical navigation was at our discretion to 8000 ft. Less confusing wording would be 'descend via tragr arrival, comply with restrs, cleared to 8000 ft after povoc.' the NOTAMS and changes to sids and stars to las vegas are constantly being amended and the clrncs from ATC seem to always vary from the STAR/sids. I was under the impression once the altitude had been amended the previous altitude restr was removed but this is incorrect on my part. Supplemental information from acn 558698: my captain and I discussed whether the next restrs (ipumy at 12000 ft MSL and povoc at 9000 ft MSL 190 KTS) were still required. At povoc, ATC requested a call after landing to 'gather data.' my captain called and the controller said we were high at povoc. I do not recall being above 9000 ft MSL at povoc, but we very well could have been at 10300 ft MSL at ipumy. The controller stated that there was no violation, but that so many flight crew's have been making the same mistake, he wanted to know what could be stated differently so that crews would follow the step-downs and cross povoc at 8000 ft MSL. As the arrival currently reads, you are supposed to cross povoc at 9000 ft and 210 KTS. The clearance was not very clear.

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Original NASA ASRS Text

Title: B737 INBOUND TO LAS ON THE TRAGR RNAV 1 ARR MISUNDERSTOOD CLRNC AND MISSED A XING RESTR.

Narrative: AFTER FUZZY, CLRED TO DSND VIA TRAGR 1 ARR EXCEPT MAINTAIN 8000 FT. WE STARTED DSCNT AND EVIDENTLY CROSSED POVOC ABOVE 9000 FT. MY UNDERSTANDING WAS THAT WE WERE TO FOLLOW SPD RESTRS BUT VERT NAV WAS AT OUR DISCRETION TO 8000 FT. LESS CONFUSING WORDING WOULD BE 'DSND VIA TRAGR ARR, COMPLY WITH RESTRS, CLRED TO 8000 FT AFTER POVOC.' THE NOTAMS AND CHANGES TO SIDS AND STARS TO LAS VEGAS ARE CONSTANTLY BEING AMENDED AND THE CLRNCS FROM ATC SEEM TO ALWAYS VARY FROM THE STAR/SIDS. I WAS UNDER THE IMPRESSION ONCE THE ALT HAD BEEN AMENDED THE PREVIOUS ALT RESTR WAS REMOVED BUT THIS IS INCORRECT ON MY PART. SUPPLEMENTAL INFO FROM ACN 558698: MY CAPT AND I DISCUSSED WHETHER THE NEXT RESTRS (IPUMY AT 12000 FT MSL AND POVOC AT 9000 FT MSL 190 KTS) WERE STILL REQUIRED. AT POVOC, ATC REQUESTED A CALL AFTER LNDG TO 'GATHER DATA.' MY CAPT CALLED AND THE CTLR SAID WE WERE HIGH AT POVOC. I DO NOT RECALL BEING ABOVE 9000 FT MSL AT POVOC, BUT WE VERY WELL COULD HAVE BEEN AT 10300 FT MSL AT IPUMY. THE CTLR STATED THAT THERE WAS NO VIOLATION, BUT THAT SO MANY FLC'S HAVE BEEN MAKING THE SAME MISTAKE, HE WANTED TO KNOW WHAT COULD BE STATED DIFFERENTLY SO THAT CREWS WOULD FOLLOW THE STEP-DOWNS AND CROSS POVOC AT 8000 FT MSL. AS THE ARR CURRENTLY READS, YOU ARE SUPPOSED TO CROSS POVOC AT 9000 FT AND 210 KTS. THE CLRNC WAS NOT VERY CLEAR.

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.