Narrative:

Let me begin by making a safety recommendation, so as to enhance 'altitude situational awareness' for aircraft conducting sids/stars, particularly in hazardous terrain. I would recommend that MEA's and MOCA's be displayed on stars and sids, by specific, applicable route segments. As an example, the attached 'fossil 6' STAR into phx is included for your review. Note that only the initial segment after the initial arrival fix has an MEA altitude. But as the fossil STAR continues toward phx (pxr), there are no MEA/MOCA altitudes displayed! There is a 7900 ft MSL obstruction located about 44 NM nne, along the 015 degree radial. Displaying MEA/MOCA information, by segment, may prevent misunderstanding and inadvertent descent into the obstruction. This almost happened to us! We were cleared via the fossil 6 STAR, with gup transition. After gup, we were subsequently cleared via the fossil 6 arrival. After crossing sacho at FL310, we were subsequently cleared direct to piine intersection. We were then cleared to cross mazat intersection at 12000 ft. After passing piine, we were cleared to cross mazat at or below 12000 ft, to maintain 8000 ft. Or were we? As we approached mazat at 11000 ft, descending to 8000 ft, the phx approach controller advised us that we had left 12000 ft prematurely, but that it was 'no problem.' I had confirmed with my first officer what we both thought was a clearance to 8000 ft, with a restr to cross mazat at or below 12000 ft. My first officer indicated that is what he thought that we had read back. Our clearance, apparently, had been to cross mazat intersection at 12000 ft, then descend to 8000 ft. In the future, lacking MEA/MOCA altitude information, I will treat the 'expect to cross' or mandated crossing altitudes, as absolute, regardless of what we are cleared to, and I will always ask ATC to verify any changes to a descent clearance, which appear to be at variance with a published or expected restr on a STAR or SID! The thought had crossed my mind as we passed 12000 ft, descending to 8000 ft, and I verbally confirmed our clearance with the first officer. If I had a doubt, I should have again verified it with ATC, but MEA, MOCA's, should be on stars and sids, segment-by-segment.

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Original NASA ASRS Text

Title: A B757-200 FLC DSNDS PREMATURELY WHEN THEIR ALT ASSIGNMENT FOR CLRNC TO CROSS MAZAT INTXN ON THE FOSSIL 6 STAR IS MISUNDERSTOOD 40 MI NNE OF PXR, AZ.

Narrative: LET ME BEGIN BY MAKING A SAFETY RECOMMENDATION, SO AS TO ENHANCE 'ALT SITUATIONAL AWARENESS' FOR ACFT CONDUCTING SIDS/STARS, PARTICULARLY IN HAZARDOUS TERRAIN. I WOULD RECOMMEND THAT MEA'S AND MOCA'S BE DISPLAYED ON STARS AND SIDS, BY SPECIFIC, APPLICABLE RTE SEGMENTS. AS AN EXAMPLE, THE ATTACHED 'FOSSIL 6' STAR INTO PHX IS INCLUDED FOR YOUR REVIEW. NOTE THAT ONLY THE INITIAL SEGMENT AFTER THE INITIAL ARR FIX HAS AN MEA ALT. BUT AS THE FOSSIL STAR CONTINUES TOWARD PHX (PXR), THERE ARE NO MEA/MOCA ALTS DISPLAYED! THERE IS A 7900 FT MSL OBSTRUCTION LOCATED ABOUT 44 NM NNE, ALONG THE 015 DEG RADIAL. DISPLAYING MEA/MOCA INFO, BY SEGMENT, MAY PREVENT MISUNDERSTANDING AND INADVERTENT DSCNT INTO THE OBSTRUCTION. THIS ALMOST HAPPENED TO US! WE WERE CLRED VIA THE FOSSIL 6 STAR, WITH GUP TRANSITION. AFTER GUP, WE WERE SUBSEQUENTLY CLRED VIA THE FOSSIL 6 ARR. AFTER XING SACHO AT FL310, WE WERE SUBSEQUENTLY CLRED DIRECT TO PIINE INTXN. WE WERE THEN CLRED TO CROSS MAZAT INTXN AT 12000 FT. AFTER PASSING PIINE, WE WERE CLRED TO CROSS MAZAT AT OR BELOW 12000 FT, TO MAINTAIN 8000 FT. OR WERE WE? AS WE APCHED MAZAT AT 11000 FT, DSNDING TO 8000 FT, THE PHX APCH CTLR ADVISED US THAT WE HAD LEFT 12000 FT PREMATURELY, BUT THAT IT WAS 'NO PROB.' I HAD CONFIRMED WITH MY FO WHAT WE BOTH THOUGHT WAS A CLRNC TO 8000 FT, WITH A RESTR TO CROSS MAZAT AT OR BELOW 12000 FT. MY FO INDICATED THAT IS WHAT HE THOUGHT THAT WE HAD READ BACK. OUR CLRNC, APPARENTLY, HAD BEEN TO CROSS MAZAT INTXN AT 12000 FT, THEN DSND TO 8000 FT. IN THE FUTURE, LACKING MEA/MOCA ALT INFO, I WILL TREAT THE 'EXPECT TO CROSS' OR MANDATED XING ALTS, AS ABSOLUTE, REGARDLESS OF WHAT WE ARE CLRED TO, AND I WILL ALWAYS ASK ATC TO VERIFY ANY CHANGES TO A DSCNT CLRNC, WHICH APPEAR TO BE AT VARIANCE WITH A PUBLISHED OR EXPECTED RESTR ON A STAR OR SID! THE THOUGHT HAD CROSSED MY MIND AS WE PASSED 12000 FT, DSNDING TO 8000 FT, AND I VERBALLY CONFIRMED OUR CLRNC WITH THE FO. IF I HAD A DOUBT, I SHOULD HAVE AGAIN VERIFIED IT WITH ATC, BUT MEA, MOCA'S, SHOULD BE ON STARS AND SIDS, SEGMENT-BY-SEGMENT.

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.