Narrative:

Air carrier X flight was cleared for the approach on runway 31L at jfk. Both pilots had the radios set with the ILS frequency 111.35 and the approach mode was selected. We were on a heading to intercept the approach. The localizer showed a full deflection but the FMS was showing captured. The airplane then started a turn to the right (the wrong direction for the approach). The autoplt was immediately disconnected and I turned the airplane back on course for the ILS. We proceeded down towards the runway and at about 1000 ft we received a full left then a full right deflection on the localizer. We executed a missed approach. The tower vectored us around for another approach. At about 800 ft we got a visual on the runway. The localizer then showed a deflection to the right even though we were aligned with the runway. We landed without incident. Maintenance was called out to work on the avionics.

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Original NASA ASRS Text

Title: CL65 CREW HAD CONFLICTING AND ERRATIC LOC INDICATIONS FOR RWY 31L AT JFK.

Narrative: ACR X FLT WAS CLRED FOR THE APCH ON RWY 31L AT JFK. BOTH PLTS HAD THE RADIOS SET WITH THE ILS FREQ 111.35 AND THE APCH MODE WAS SELECTED. WE WERE ON A HDG TO INTERCEPT THE APCH. THE LOC SHOWED A FULL DEFLECTION BUT THE FMS WAS SHOWING CAPTURED. THE AIRPLANE THEN STARTED A TURN TO THE R (THE WRONG DIRECTION FOR THE APCH). THE AUTOPLT WAS IMMEDIATELY DISCONNECTED AND I TURNED THE AIRPLANE BACK ON COURSE FOR THE ILS. WE PROCEEDED DOWN TOWARDS THE RWY AND AT ABOUT 1000 FT WE RECEIVED A FULL L THEN A FULL R DEFLECTION ON THE LOC. WE EXECUTED A MISSED APCH. THE TWR VECTORED US AROUND FOR ANOTHER APCH. AT ABOUT 800 FT WE GOT A VISUAL ON THE RWY. THE LOC THEN SHOWED A DEFLECTION TO THE R EVEN THOUGH WE WERE ALIGNED WITH THE RWY. WE LANDED WITHOUT INCIDENT. MAINT WAS CALLED OUT TO WORK ON THE AVIONICS.

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.