Narrative:

We departed phl bound for phx. Approaching phx, albuquerque center cleared us for the fossil one arrival with a crossing restriction at tonto (srp 010 degree/33) of 12000' and 250 KIAS. Subsequently we were sent over to phx approach on frequency 128.65. Approaching tonto, approach cleared us as follows (?): 'at tonto cleared pilots discretion to cross 17 mi arc at or above 8000', descend and maintain 7000'.' initially the clearance was read back incorrectly as cross 17 mi at or below 8000' descend to 7000'. Approach corrected the readback but the 'at tonto' portion was not clear in our minds. Confusion ensued as to whether or not we were immediately cleared to 8000' by 17 mi or if the altitude restriction at tonto still applied. By this time we were a few mi from tonto and descended below 12000'. When we hit tonto, approach idented the point for us as to imply we might be below assigned altitude however, no mention of it was made at the time. Upon landing, approach was contacted and it was learned that while no traffic conflict occurred, the controller did want us to comply with the altitude restriction at tonto before descending further. In retrospect, I think confusion arose over what the controller wanted us to do but a timely query would have resolved the problem. However, once again I question the wisdom of multiple altitudes and distances given in one clearance particularly when there did not appear to be an operational necessity to do so. It appeared that approach was not excessively busy requiring a long, involved clearance. I personally feel the simpler the clearance, the easier it is to follow thus enhancing the safety of the system for everyone.

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Original NASA ASRS Text

Title: ACR CONFUSED OVER WORDING OF DESCENT CLRNC DESCENDS BELOW ASSIGNED.

Narrative: WE DEPARTED PHL BOUND FOR PHX. APCHING PHX, ALBUQUERQUE CTR CLRED US FOR THE FOSSIL ONE ARR WITH A XING RESTRICTION AT TONTO (SRP 010 DEG/33) OF 12000' AND 250 KIAS. SUBSEQUENTLY WE WERE SENT OVER TO PHX APCH ON FREQ 128.65. APCHING TONTO, APCH CLRED US AS FOLLOWS (?): 'AT TONTO CLRED PLTS DISCRETION TO CROSS 17 MI ARC AT OR ABOVE 8000', DSND AND MAINTAIN 7000'.' INITIALLY THE CLRNC WAS READ BACK INCORRECTLY AS CROSS 17 MI AT OR BELOW 8000' DSND TO 7000'. APCH CORRECTED THE READBACK BUT THE 'AT TONTO' PORTION WAS NOT CLR IN OUR MINDS. CONFUSION ENSUED AS TO WHETHER OR NOT WE WERE IMMEDIATELY CLRED TO 8000' BY 17 MI OR IF THE ALT RESTRICTION AT TONTO STILL APPLIED. BY THIS TIME WE WERE A FEW MI FROM TONTO AND DSNDED BELOW 12000'. WHEN WE HIT TONTO, APCH IDENTED THE POINT FOR US AS TO IMPLY WE MIGHT BE BELOW ASSIGNED ALT HOWEVER, NO MENTION OF IT WAS MADE AT THE TIME. UPON LNDG, APCH WAS CONTACTED AND IT WAS LEARNED THAT WHILE NO TFC CONFLICT OCCURRED, THE CTLR DID WANT US TO COMPLY WITH THE ALT RESTRICTION AT TONTO BEFORE DSNDING FURTHER. IN RETROSPECT, I THINK CONFUSION AROSE OVER WHAT THE CTLR WANTED US TO DO BUT A TIMELY QUERY WOULD HAVE RESOLVED THE PROB. HOWEVER, ONCE AGAIN I QUESTION THE WISDOM OF MULTIPLE ALTS AND DISTANCES GIVEN IN ONE CLRNC PARTICULARLY WHEN THERE DID NOT APPEAR TO BE AN OPERATIONAL NECESSITY TO DO SO. IT APPEARED THAT APCH WAS NOT EXCESSIVELY BUSY REQUIRING A LONG, INVOLVED CLRNC. I PERSONALLY FEEL THE SIMPLER THE CLRNC, THE EASIER IT IS TO FOLLOW THUS ENHANCING THE SAFETY OF THE SYS FOR EVERYONE.

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.