Narrative:

We were assigned heading 280 degrees, maintain at or above 3000 ft until established on final approach course, cleared for ILS. We were in VMC at dawn. Bfi vicinity in sight, but not runway. At approximately 3 mi east of localizer, heading bug swung to 310 degrees, flight director and autoplt turned toward 310 degrees. Localizer not captured and EFIS map indicated we were not on localizer. Autoplt disengaged prior to 10 degree turn and heading returned to 280 degrees. First officer selected raw data. This confirmed position east of localizer. (This happened with localizer armed.) approach armed at this time. Heading bug again turned to 310 degrees and flight director indicated right turn. Airplane hand flown to intercept approach. Flight director corrected at this time and flew normally to landing. I was told on ground that this was an anomaly with ichj localizer and had happened before. Later that day, bfi controllers were asked about this and they said they did not know about it. Callback conversation with reporter revealed the following information: reporter said that there was no 'case break' of the localizer and yet the autoflt performed as if there was a capture of the localizer by slewing the heading bug to the localizer track and beginning a turn with the autoplt. A manual disconnect of the system was made and hand flown to localizer and for the rest of the approach. Discussion on the ground found that TRACON was not aware of any problems. It was learned that other company pilots have noticed this anomaly at bfi on the runway 31L localizer. The airline company is investigating along with boeing. It is not known if there was vehicle or other traffic in the area of the localizer transmitter.

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Original NASA ASRS Text

Title: B767, WITH AUTOFLT ARMED, HAS FALSE CAPTURE OF LOC AT BFI, WA.

Narrative: WE WERE ASSIGNED HDG 280 DEGS, MAINTAIN AT OR ABOVE 3000 FT UNTIL ESTABLISHED ON FINAL APCH COURSE, CLRED FOR ILS. WE WERE IN VMC AT DAWN. BFI VICINITY IN SIGHT, BUT NOT RWY. AT APPROX 3 MI E OF LOC, HDG BUG SWUNG TO 310 DEGS, FLT DIRECTOR AND AUTOPLT TURNED TOWARD 310 DEGS. LOC NOT CAPTURED AND EFIS MAP INDICATED WE WERE NOT ON LOC. AUTOPLT DISENGAGED PRIOR TO 10 DEG TURN AND HDG RETURNED TO 280 DEGS. FO SELECTED RAW DATA. THIS CONFIRMED POS E OF LOC. (THIS HAPPENED WITH LOC ARMED.) APCH ARMED AT THIS TIME. HDG BUG AGAIN TURNED TO 310 DEGS AND FLT DIRECTOR INDICATED R TURN. AIRPLANE HAND FLOWN TO INTERCEPT APCH. FLT DIRECTOR CORRECTED AT THIS TIME AND FLEW NORMALLY TO LNDG. I WAS TOLD ON GND THAT THIS WAS AN ANOMALY WITH ICHJ LOC AND HAD HAPPENED BEFORE. LATER THAT DAY, BFI CTLRS WERE ASKED ABOUT THIS AND THEY SAID THEY DID NOT KNOW ABOUT IT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAID THAT THERE WAS NO 'CASE BREAK' OF THE LOC AND YET THE AUTOFLT PERFORMED AS IF THERE WAS A CAPTURE OF THE LOC BY SLEWING THE HDG BUG TO THE LOC TRACK AND BEGINNING A TURN WITH THE AUTOPLT. A MANUAL DISCONNECT OF THE SYS WAS MADE AND HAND FLOWN TO LOC AND FOR THE REST OF THE APCH. DISCUSSION ON THE GND FOUND THAT TRACON WAS NOT AWARE OF ANY PROBS. IT WAS LEARNED THAT OTHER COMPANY PLTS HAVE NOTICED THIS ANOMALY AT BFI ON THE RWY 31L LOC. THE AIRLINE COMPANY IS INVESTIGATING ALONG WITH BOEING. IT IS NOT KNOWN IF THERE WAS VEHICLE OR OTHER TFC IN THE AREA OF THE LOC XMITTER.

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.