Narrative:

While descending into bfi on the JAWBN1 arrival; we descended below one of the published altitudes. It was a mandatory altitude published on the chart; and we were told to descend via the arrival. The altitude was supposed to be jawbn at 16000 ft; but we managed to cross it at 14000 ft. ATC controller told us not to worry about it and just level off at 14000 ft. How did it happen? The jawbn fix has 2 different altitudes published -- 1 for landing north (16000 ft); and 1 for landing south (11000 ft). While en route to bfi; we looked at the WX; and the winds were favoring landing south. We set the FMS up to land south; and the 11000 ft altitude was automatically put in the FMS. We diligently verified the crossing altitudes in the FMS for accuracy. Shortly afterwards; we received the ATIS; and it said they were landing north. We changed the FMS for a north landing; but we neglected to verify the altitude at jawbn changed from 11000 ft to 16000 ft. We must have got busy; and I saw the heading to depart the last fix on the arrival 'did' change when we switched the runway. Because of this; I assumed the crossing altitude also changed; but it didn't. I noticed the error as we descended through about 14500 ft. I fessed up to the controller; who said to level off at present altitude (14000 ft); and that it was not a big deal this time. She also said to be careful in the future. I'm reporting this for several reasons; but one is because of an FMS flaw that was a contributing factor. I duplicated this on the ground; so I'm positive the FMS will not change published altitudes when you switch runways (at least not for the JAWBN1 arrival into bfi). Also; I find it odd that the outbound heading 'does' change when you switch runways. So; it changes half of what needs to change. We saw the half that did change; and incorrectly assumed it all changed.

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Original NASA ASRS Text

Title: CE650 FLT CREW LEARNS THE IDIOSYNCRASIES OF THE CE650 FMC DURING THE JAWBN 1 ARRIVAL TO BFI AFTER CHANGING THE LANDING RWY. JAWBN CROSSING RESTRICTION IS NOT MET.

Narrative: WHILE DSNDING INTO BFI ON THE JAWBN1 ARR; WE DSNDED BELOW ONE OF THE PUBLISHED ALTS. IT WAS A MANDATORY ALT PUBLISHED ON THE CHART; AND WE WERE TOLD TO DSND VIA THE ARR. THE ALT WAS SUPPOSED TO BE JAWBN AT 16000 FT; BUT WE MANAGED TO CROSS IT AT 14000 FT. ATC CTLR TOLD US NOT TO WORRY ABOUT IT AND JUST LEVEL OFF AT 14000 FT. HOW DID IT HAPPEN? THE JAWBN FIX HAS 2 DIFFERENT ALTS PUBLISHED -- 1 FOR LNDG N (16000 FT); AND 1 FOR LNDG S (11000 FT). WHILE ENRTE TO BFI; WE LOOKED AT THE WX; AND THE WINDS WERE FAVORING LNDG S. WE SET THE FMS UP TO LAND S; AND THE 11000 FT ALT WAS AUTOMATICALLY PUT IN THE FMS. WE DILIGENTLY VERIFIED THE XING ALTS IN THE FMS FOR ACCURACY. SHORTLY AFTERWARDS; WE RECEIVED THE ATIS; AND IT SAID THEY WERE LNDG N. WE CHANGED THE FMS FOR A N LNDG; BUT WE NEGLECTED TO VERIFY THE ALT AT JAWBN CHANGED FROM 11000 FT TO 16000 FT. WE MUST HAVE GOT BUSY; AND I SAW THE HDG TO DEPART THE LAST FIX ON THE ARR 'DID' CHANGE WHEN WE SWITCHED THE RWY. BECAUSE OF THIS; I ASSUMED THE XING ALT ALSO CHANGED; BUT IT DIDN'T. I NOTICED THE ERROR AS WE DSNDED THROUGH ABOUT 14500 FT. I FESSED UP TO THE CTLR; WHO SAID TO LEVEL OFF AT PRESENT ALT (14000 FT); AND THAT IT WAS NOT A BIG DEAL THIS TIME. SHE ALSO SAID TO BE CAREFUL IN THE FUTURE. I'M RPTING THIS FOR SEVERAL REASONS; BUT ONE IS BECAUSE OF AN FMS FLAW THAT WAS A CONTRIBUTING FACTOR. I DUPLICATED THIS ON THE GND; SO I'M POSITIVE THE FMS WILL NOT CHANGE PUBLISHED ALTS WHEN YOU SWITCH RWYS (AT LEAST NOT FOR THE JAWBN1 ARR INTO BFI). ALSO; I FIND IT ODD THAT THE OUTBOUND HDG 'DOES' CHANGE WHEN YOU SWITCH RWYS. SO; IT CHANGES HALF OF WHAT NEEDS TO CHANGE. WE SAW THE HALF THAT DID CHANGE; AND INCORRECTLY ASSUMED IT ALL CHANGED.

Data retrieved from NASA's ASRS site as of May 2009 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.