Narrative:

I have flown to scel (santiago chile) dozens of times and when you engage approach from LNAV; 90% of the time; the jets breaks right about 5 degrees and then south turns a couple times until settling down on the localizer (never any issues with the glideslope). Today's flight on final to scel performing an ILS Z runway 17L catiii approach (weather 400m ovc 200 ft; I was pilot flying and we briefed that once configured the captain would take over and we'd perform a catiii autoland); about 12 miles out we engaged approach and the jet broke hard right (approximately 15 degree bank) our ILS (localizer) broke lock and we got the amber boxed localizer which forced the jet to just keep going wings level. At that time; we got a call from tower asking us if we were lining up on 17R; we answered that our aircraft had an instrument problem and we were correcting; I clicked off the autopilot and corrected back to the course manually. Once stabilized; I re-engaged the autopilot and the jet started breaking right again so at approximately 1;000 AGL; I initiated a go-around and we climbed out uneventful. On downwind; the weather improved to cati mins (600m and ovc 250 ft) so we were cleared ILS Y 17L cati and again; we waited until we were a little closer but once we engaged app mode; the jet broke hard right approximately 15 degrees and we immediately disconnected the autopilot; flew manually back to course; engaged LNAV to bring us even closer to the ILS signal; reset both flight directors which recentered the lateral guidance; and continued the approach until about 1;000 AGL where the system 'seemed' to settle down. We re-engaged ILS and the autopilot; and the jet flew 'so so' until about 300 ft where I called approaching minimums and we saw the approach lights and runway (we were about 30 ft left of course); the captain disconnected the autopilot; manually corrected to centerline and we landed uneventful.this was the most uncomfortable I've ever been in any jet as with most emergencies/abnormals there are procedures; you fly them and run the checklist and that's that. This is the type of setup/error chain that gets people killed because there are no procedures; mountainous terrain; low visibility and a known anomaly with a fleet that is sent down here every day year around. We spoke to two other crews that landed before and after and neither had the same issue; so it was most definitely aircraft specific.

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Original NASA ASRS Text

Title: B767 flight crew reported erratic localizer movement on the SCEL ILS Runway 17L which caused a go-around on the first approach and eventually a successful landing on the second approach.

Narrative: I have flown to SCEL (Santiago Chile) dozens of times and when you engage approach from LNAV; 90% of the time; the jets breaks right about 5 degrees and then S turns a couple times until settling down on the LOC (never any issues with the glideslope). Today's flight on final to SCEL performing an ILS Z Runway 17L CATIII approach (Weather 400m OVC 200 ft; I was pilot flying and we briefed that once configured the captain would take over and we'd perform a CATIII autoland); about 12 miles out we engaged approach and the jet broke hard right (approximately 15 degree bank) our ILS (LOC) broke lock and we got the amber boxed LOC which forced the jet to just keep going wings level. At that time; we got a call from tower asking us if we were lining up on 17R; we answered that our aircraft had an instrument problem and we were correcting; I clicked off the autopilot and corrected back to the course manually. Once stabilized; I re-engaged the autopilot and the jet started breaking right again so at approximately 1;000 AGL; I initiated a go-around and we climbed out uneventful. On downwind; the Weather improved to CATI mins (600m and OVC 250 ft) so we were cleared ILS Y 17L CATI and again; we waited until we were a little closer but once we engaged APP mode; the jet broke hard right approximately 15 degrees and we immediately disconnected the autopilot; flew manually back to course; engaged LNAV to bring us even closer to the ILS signal; reset both flight directors which recentered the lateral guidance; and continued the approach until about 1;000 AGL where the system 'seemed' to settle down. We re-engaged ILS and the autopilot; and the jet flew 'so so' until about 300 ft where I called approaching minimums and we saw the approach lights and runway (we were about 30 ft left of course); the captain disconnected the autopilot; manually corrected to centerline and we landed uneventful.This was the most uncomfortable I've ever been in any jet as with most emergencies/abnormals there are procedures; you fly them and run the checklist and that's that. This is the type of setup/error chain that gets people killed because there are no procedures; mountainous terrain; low visibility and a known anomaly with a fleet that is sent down here every day year around. We spoke to two other crews that landed before and after and neither had the same issue; so it was most definitely aircraft specific.

Data retrieved from NASA's ASRS site 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.