Narrative:

Upon being cleared for the ILS 24R in lax; I armed the VOR/localizer to capture the localizer. After recognizing; on the nd (navigation display); that the aircraft wasn't going to capture it (after two positive identification's); I disconnected the B autopilot and steepened the bank angle to rejoin. At that time; my FD (flight director) course went blank and ATC said we were left of course; and we had traffic south of us lining up for the south runways (25L). After rejoining close to the inbound heading; I could not rejoin the localizer by navigation or LNAV via hand flying; so I elected to transfer the controls to the captain; pm (pilot monitoring); because his flight instruments were not acting erroneously. He took the flight controls and elected to descend on the glidepath; but at that time was off course to the right and 400 ft. Low crossing jetsa (2;200 ft.). ATC advised us again of our course deviation (now to the right) but never altitude deviation below glidepath. At that point; we elected to fly the missed approach and ATC gave us a heading; altitude and subsequent radar vectors to fly the 24R ILS a second time. We noticed the first officer (first officer) side localizer and GS indications were inaccurate and the FD course disappeared where localizer intercept should have been. Therefore; the captain flew the approach via 'a' autopilot and landed uneventfully.at the gate; a maintenance writeup was entered in the aircraft logbook and maintenance control was notified. I do not believe this course deviation was a result of bad piloting. The aircraft 'B' autopilot was not responding to the navigation inputs of the PF (pilot flying). This was clearly an aircraft malfunction. However; if both pilots would have recognized it seconds earlier; then maybe a selection of the other pilot's autopilot (a) and re-arming VOR/localizer or LNAV could have mitigated the problem.

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Original NASA ASRS Text

Title: B-737 flight crew reported experiencing course control problems during ILS approach due to autopilot malfunction.

Narrative: Upon being cleared for the ILS 24R in LAX; I armed the VOR/LOC to capture the Localizer. After recognizing; on the ND (Navigation Display); that the aircraft wasn't going to capture it (after two positive ID's); I disconnected the B Autopilot and steepened the bank angle to rejoin. At that time; my FD (Flight Director) course went blank and ATC said we were left of course; and we had traffic south of us lining up for the south runways (25L). After rejoining close to the inbound heading; I could not rejoin the localizer by NAV or LNAV via hand flying; so I elected to transfer the controls to the Captain; PM (Pilot Monitoring); because his flight instruments were not acting erroneously. He took the flight controls and elected to descend on the glidepath; but at that time was off course to the right and 400 ft. low crossing JETSA (2;200 ft.). ATC advised us again of our course deviation (now to the right) but never altitude deviation below glidepath. At that point; we elected to fly the missed approach and ATC gave us a heading; altitude and subsequent radar vectors to fly the 24R ILS a second time. We noticed the FO (First Officer) side LOC and GS indications were inaccurate and the FD course disappeared where localizer intercept should have been. Therefore; the Captain flew the approach via 'A' Autopilot and landed uneventfully.At the gate; a maintenance writeup was entered in the aircraft logbook and Maintenance Control was notified. I do not believe this course deviation was a result of bad piloting. The aircraft 'B' Autopilot was not responding to the navigation inputs of the PF (Pilot Flying). This was clearly an aircraft malfunction. However; if both pilots would have recognized it seconds earlier; then maybe a selection of the other pilot's autopilot (A) and re-arming VOR/LOC or LNAV could have mitigated the problem.

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.