B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 1746
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Aircraft
We began the ILS 25L into LAX from SEAVU and were established in LNAV and VNAV Path. The PF selected approach mode on an intercept heading. Upon selection; the aircraft immediately captured LOC mode in the FMA and instituted a right turn almost 45 degrees across the localizer when it should have turned left to join. The autopilot was disconnected while I double checked the frequency and course of the ILS. We were queried by ATC and told to rejoin on a heading which we complied with. The autopilot was reengaged on the intercept heading from the north and proceeded to capture the LOC FMA and turn right (north) away from the course. The autopilot was disconnected again and we reassessed everything a second time. ATC offered 24R if it would help but we declined as we were still troubleshooting. The guidance provided by the flight director in the approach mode was not even close to what was required to rejoin. The PF elected to hand fly it from the final approach fix where Flight Director Approach guidance was telling him he was correct but we were lined up on a taxiway south of 25R. He corrected promptly and we landed without exceeding our stabilized approach criteria. The aircraft malfunction was written up on arrival to the gate. The malfunction by the autoflight caused us to be north of course by an undetermined amount. This report is just in case any loss of separation occurred inadvertently.
[Report narrative contained no additional information.]
B757 flight crew reported difficulties with the autoflight function to keep on the LAX Runway 25L ILS centerline.