Date: 201908
Local time of day: 0001-0600
Location: LAX.Airport, CA
Flight conditions: Mixed
Weather elements / visibility: 0.25
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B LAX
ATC / advisory: TRACON SCT
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Troubleshooting; Confusion
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Unstabilized Approach
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

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.


Second narrative: First Officer was Pilot Flying and we were being vectored to intercept 24R LOC for the ILS approach; given a 225 degree heading to intercept and subsequently cleared for the ILS approach. The PFD showed the correct identifier and the FMA (Flight Mode Annunciator) displayed the normal indications. The aircraft did not capture the localizer or glideslope. By the time we had intervened manually we had drifted toward the 25L final causing a call from ATC. We were given a traffic alert of an aircraft on 25L final to which we responded 'in sight.' We attempted to continue the approach manually while troubleshooting our instrument setup; verifying it was correct. The aircraft never would capture the LOC or GS and LAX Final Controller gave us another call that we were now right of course.The FO (First Officer) initiated a control change to me because his LOC indications on the PFD were erratic. I was more outside the aircraft looking at traffic and; admittedly; not ready to assume controls but did anyway because he seemed to be in the red. While trying to establish my scan and get myself into the green we decided to execute a go-around; initiating it at approximately 1300 ft. MSL. Our missed approach instructions were to level at 2000 ft. Because I was still in the red and under a high task load; we did not stop our climb until approximately 2300 ft. and descended back to 2000 ft. There were no TA/RA Alerts received or altitude calls from ATC. We were vectored back around for another approach which I flew without problem. We did notice that the FO's LOC indication in the PFD disappeared for a few seconds around the time of course intercept. We determined that must have been the cause of the aircraft not capturing the ILS on his attempt. A defect entry in the logbook was made. The biggest mistake we made was not executing a go-around sooner. Because we were in IMC and also in a high traffic area as soon as the aircraft did not capture the final approach course we should have not tried to troubleshoot and salvage the approach. The better course of action without the runway in sight would have simply been to go-around and do our troubleshooting there.


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