Narrative:

Center was descending us in 2000' increments into the pittsburg area. We were requested to keep our speed up. Level at 15000' we were instructed to cross nesto intersection at 9000' which only gave us 12 mi to descend and slow. The PNF accepted the clearance but we quickly realized we could not comply. Informing the controller we could not meet the restriction we were told to do the best we could. I instructed the PNF to inform the controller we could not accept this phraseology and now needed a new specific clearance. After 2 attempts at trying to get our point across we had reached nesto but not at 9000'. The term do the best you can is often used and leads me to understand just that. In other words, if the clearance is not met, no problem, no conflict, no violation. However, it has been brought to my attention that do the best you can is not an acceptable clearance and by not meeting the original clearance of nesto at 9000' leaves one open for a violation. The problem arises when in a short span of time such as this it is difficult to have the clearance revised because the controller is satisfied as he has issued do the best you can. Either the phraseology should not be used or it should be considered an acceptable clearance meaning the restriction no longer is required.

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Original NASA ASRS Text

Title: MLG GIVEN DESCENT AND CROSSING RESTRICTION LATE, UNABLE TO MAKE RESTRICTION AND DIDN'T LIKE PHRASEOLOGY USED BY ARTCC CTLR.

Narrative: CENTER WAS DSNDING US IN 2000' INCREMENTS INTO THE PITTSBURG AREA. WE WERE REQUESTED TO KEEP OUR SPD UP. LEVEL AT 15000' WE WERE INSTRUCTED TO CROSS NESTO INTXN AT 9000' WHICH ONLY GAVE US 12 MI TO DSND AND SLOW. THE PNF ACCEPTED THE CLRNC BUT WE QUICKLY REALIZED WE COULD NOT COMPLY. INFORMING THE CTLR WE COULD NOT MEET THE RESTRICTION WE WERE TOLD TO DO THE BEST WE COULD. I INSTRUCTED THE PNF TO INFORM THE CTLR WE COULD NOT ACCEPT THIS PHRASEOLOGY AND NOW NEEDED A NEW SPECIFIC CLRNC. AFTER 2 ATTEMPTS AT TRYING TO GET OUR POINT ACROSS WE HAD REACHED NESTO BUT NOT AT 9000'. THE TERM DO THE BEST YOU CAN IS OFTEN USED AND LEADS ME TO UNDERSTAND JUST THAT. IN OTHER WORDS, IF THE CLRNC IS NOT MET, NO PROB, NO CONFLICT, NO VIOLATION. HOWEVER, IT HAS BEEN BROUGHT TO MY ATTN THAT DO THE BEST YOU CAN IS NOT AN ACCEPTABLE CLRNC AND BY NOT MEETING THE ORIGINAL CLRNC OF NESTO AT 9000' LEAVES ONE OPEN FOR A VIOLATION. THE PROB ARISES WHEN IN A SHORT SPAN OF TIME SUCH AS THIS IT IS DIFFICULT TO HAVE THE CLRNC REVISED BECAUSE THE CTLR IS SATISFIED AS HE HAS ISSUED DO THE BEST YOU CAN. EITHER THE PHRASEOLOGY SHOULD NOT BE USED OR IT SHOULD BE CONSIDERED AN ACCEPTABLE CLRNC MEANING THE RESTRICTION NO LONGER IS REQUIRED.

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.