Narrative:

The circumstances that brought this to light occurred while we were in cruise at FL290. ATC issued a clearance for us to cross dny at FL180. I read back the clearance to 'cross dny at FL180' and we immediately set FL180 in the altitude preselector, confirmed it between ourselves, and started down. In my mind, we had acknowledged/read back the clearance and ATC knew we had started down right away. And even if we had delayed in descending, since this was a form of pilot's discretion, I did not believe any further report would be required. The frequency became quite busy as we started down and as we passed FL272 ATC finished with 1 aircraft and then said 'and (airline/flight) you called out of FL290.' I immediately answered affirmative and told ATC that we had indeed started down. Then I started thinking about the exact question ATC had asked and realized that a specific call using the words 'leaving FL290' may very well have been what he was expecting. This prompted much searching through the far/aim book, once back home, in an attempt to find the passage absolving pilot requirement of the leaving previously assigned altitude call to ATC when complying with a 'pilot's discretion' clearance. So, from now on, the phraseology will be 'leaving (previously assigned altitude) for (newly assigned altitude), (airline/flight).' this will apply to both regular altitude clrncs and pilot's discretion/crossing restr altitude clrncs. That way, there will be less, and hopefully no, ambiguity.

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Original NASA ASRS Text

Title: CL65 FO DID NOT USE THE EXACT AIM PHRASEOLOGY WHEN VACATING AN ALT.

Narrative: THE CIRCUMSTANCES THAT BROUGHT THIS TO LIGHT OCCURRED WHILE WE WERE IN CRUISE AT FL290. ATC ISSUED A CLRNC FOR US TO CROSS DNY AT FL180. I READ BACK THE CLRNC TO 'CROSS DNY AT FL180' AND WE IMMEDIATELY SET FL180 IN THE ALT PRESELECTOR, CONFIRMED IT BTWN OURSELVES, AND STARTED DOWN. IN MY MIND, WE HAD ACKNOWLEDGED/READ BACK THE CLRNC AND ATC KNEW WE HAD STARTED DOWN RIGHT AWAY. AND EVEN IF WE HAD DELAYED IN DSNDING, SINCE THIS WAS A FORM OF PLT'S DISCRETION, I DID NOT BELIEVE ANY FURTHER RPT WOULD BE REQUIRED. THE FREQ BECAME QUITE BUSY AS WE STARTED DOWN AND AS WE PASSED FL272 ATC FINISHED WITH 1 ACFT AND THEN SAID 'AND (AIRLINE/FLT) YOU CALLED OUT OF FL290.' I IMMEDIATELY ANSWERED AFFIRMATIVE AND TOLD ATC THAT WE HAD INDEED STARTED DOWN. THEN I STARTED THINKING ABOUT THE EXACT QUESTION ATC HAD ASKED AND REALIZED THAT A SPECIFIC CALL USING THE WORDS 'LEAVING FL290' MAY VERY WELL HAVE BEEN WHAT HE WAS EXPECTING. THIS PROMPTED MUCH SEARCHING THROUGH THE FAR/AIM BOOK, ONCE BACK HOME, IN AN ATTEMPT TO FIND THE PASSAGE ABSOLVING PLT REQUIREMENT OF THE LEAVING PREVIOUSLY ASSIGNED ALT CALL TO ATC WHEN COMPLYING WITH A 'PLT'S DISCRETION' CLRNC. SO, FROM NOW ON, THE PHRASEOLOGY WILL BE 'LEAVING (PREVIOUSLY ASSIGNED ALT) FOR (NEWLY ASSIGNED ALT), (AIRLINE/FLT).' THIS WILL APPLY TO BOTH REGULAR ALT CLRNCS AND PLT'S DISCRETION/XING RESTR ALT CLRNCS. THAT WAY, THERE WILL BE LESS, AND HOPEFULLY NO, AMBIGUITY.

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.