Narrative:

We were a flight from phx to dtw. We were given the mizar 3 arrival over lfd. The flight was approaching lfd in a descent to cross mizar at 12000 ft. Approximately flight altitude was in the mid 20's. The aircraft speed was about 315 KIAS with a large tailwind. The A320 computed a turn radius that eventually turned the aircraft to miss lfd by about 5 mi. Outbound on the arrival, the controller (in a rather dry manner) asked us what our routing was. We replied that it was the mizar 3 over lfd. The controller then informed us that we had missed lfd by 5 mi. With little hesitation, the first officer responded that we had overflown lfd. After some discussion between the first officer and myself, we decided not to discuss who was right or wrong in the matter over the radio. Shortly afterwards, the controller vectored us off the arrival for a few mi and then had us fly direct to mizar. As far as I know, there were no traffic conflicts. The controller seemed perturbed, but never brought up the subject again. After the trip, I brought up the issue with one of our A320 chief pilots. He informed me that the issue is vague. I then looked up the subject in the online aim. Here, too, the issue is convoluted as leading turns are expected to help keep the aircraft within the 4 NM limit of the airway. But this only applies below FL180. Above FL180 there appears to be no such limit. Additionally, we were not on an airway as we were cleared direct to lfd to begin the arrival. Many other A320 crew members have had similar sits. The airbus FMGS software plans for a 25 degree bank turn at 1G and can and does make large leading turns -- especially at high altitude with a tailwind. Because of this, the fom states that crews may have to make additional flight plan inputs so as to help the aircraft remain within the airway limits if those limits apply. I find this odd, as the A320 aircraft and its software are certified to operate in united states airspace. Nevertheless, in the future, I will try to assist the aircraft in its flight path any time such aircraft derived flight path may be questioned.

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Original NASA ASRS Text

Title: A320 FLC EXCEEDS AIRWAYS BOUNDARIES DURING STAR INTO DTW.

Narrative: WE WERE A FLT FROM PHX TO DTW. WE WERE GIVEN THE MIZAR 3 ARR OVER LFD. THE FLT WAS APCHING LFD IN A DSCNT TO CROSS MIZAR AT 12000 FT. APPROX FLT ALT WAS IN THE MID 20'S. THE ACFT SPD WAS ABOUT 315 KIAS WITH A LARGE TAILWIND. THE A320 COMPUTED A TURN RADIUS THAT EVENTUALLY TURNED THE ACFT TO MISS LFD BY ABOUT 5 MI. OUTBOUND ON THE ARR, THE CTLR (IN A RATHER DRY MANNER) ASKED US WHAT OUR ROUTING WAS. WE REPLIED THAT IT WAS THE MIZAR 3 OVER LFD. THE CTLR THEN INFORMED US THAT WE HAD MISSED LFD BY 5 MI. WITH LITTLE HESITATION, THE FO RESPONDED THAT WE HAD OVERFLOWN LFD. AFTER SOME DISCUSSION BTWN THE FO AND MYSELF, WE DECIDED NOT TO DISCUSS WHO WAS RIGHT OR WRONG IN THE MATTER OVER THE RADIO. SHORTLY AFTERWARDS, THE CTLR VECTORED US OFF THE ARR FOR A FEW MI AND THEN HAD US FLY DIRECT TO MIZAR. AS FAR AS I KNOW, THERE WERE NO TFC CONFLICTS. THE CTLR SEEMED PERTURBED, BUT NEVER BROUGHT UP THE SUBJECT AGAIN. AFTER THE TRIP, I BROUGHT UP THE ISSUE WITH ONE OF OUR A320 CHIEF PLTS. HE INFORMED ME THAT THE ISSUE IS VAGUE. I THEN LOOKED UP THE SUBJECT IN THE ONLINE AIM. HERE, TOO, THE ISSUE IS CONVOLUTED AS LEADING TURNS ARE EXPECTED TO HELP KEEP THE ACFT WITHIN THE 4 NM LIMIT OF THE AIRWAY. BUT THIS ONLY APPLIES BELOW FL180. ABOVE FL180 THERE APPEARS TO BE NO SUCH LIMIT. ADDITIONALLY, WE WERE NOT ON AN AIRWAY AS WE WERE CLRED DIRECT TO LFD TO BEGIN THE ARR. MANY OTHER A320 CREW MEMBERS HAVE HAD SIMILAR SITS. THE AIRBUS FMGS SOFTWARE PLANS FOR A 25 DEG BANK TURN AT 1G AND CAN AND DOES MAKE LARGE LEADING TURNS -- ESPECIALLY AT HIGH ALT WITH A TAILWIND. BECAUSE OF THIS, THE FOM STATES THAT CREWS MAY HAVE TO MAKE ADDITIONAL FLT PLAN INPUTS SO AS TO HELP THE ACFT REMAIN WITHIN THE AIRWAY LIMITS IF THOSE LIMITS APPLY. I FIND THIS ODD, AS THE A320 ACFT AND ITS SOFTWARE ARE CERTIFIED TO OPERATE IN UNITED STATES AIRSPACE. NEVERTHELESS, IN THE FUTURE, I WILL TRY TO ASSIST THE ACFT IN ITS FLT PATH ANY TIME SUCH ACFT DERIVED FLT PATH MAY BE QUESTIONED.

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.