A300 flight crew reported that an autopilot malfunction resulted in a course deviation.

Narrative:

IMC arrival. After several vectors for spacing; and speed changes; we were given a heading of 320 degrees to join the localizer; maintain 3;000 ft. And cleared the ILS. Sometimes; an airbus flight director does not like large turns to join a localizer; this was one of those cases. Our aircraft indicated 'localizer STAR' meaning it was joining the localizer; yet the aircraft continued a right turn through the localizer course and a further 20 deg right. I immediately noticed the deviation; and directed the first officer to disconnect the autopilot and turn left back on course. Our CDI indicated a max deviation of 1.5 dots right of course. When; while hand flying; we were centered on the localizer once again; we re-automated the aircraft. Remainder of the ILS was normal. Later that same night; I got a phone call from the [chief pilot] stating that TRACON wanted to speak with me; saying we had left an ILS and returned without clearance. I called TRACON and explained the situation above. Once I told him that our max deviation was 1.5 dots (meaning we were on the localizer at all times while correcting back to centerline) he was relieved and stated 'ok that's all I need to know.'I have experienced this problem with airbus flight directors before and written them up; and the clearing action is always 'cannot duplicate the error'. Even the [chief pilot] said he has experienced this same problem.

Original NASA ASRS Text

Title: A300 flight crew reported that an autopilot malfunction resulted in a course deviation.

Narrative: IMC arrival. After several vectors for spacing; and speed changes; we were given a heading of 320 degrees to join the LOC; maintain 3;000 ft. and cleared the ILS. Sometimes; an Airbus Flight Director does not like large turns to join a LOC; this was one of those cases. Our aircraft indicated 'LOC STAR' meaning it was joining the LOC; yet the aircraft continued a right turn through the LOC course and a further 20 deg right. I immediately noticed the deviation; and directed the First Officer to disconnect the autopilot and turn left back on course. Our CDI indicated a max deviation of 1.5 dots right of course. When; while hand flying; we were centered on the LOC once again; we re-automated the aircraft. Remainder of the ILS was normal. Later that same night; I got a phone call from the [Chief Pilot] stating that TRACON wanted to speak with me; saying we had left an ILS and returned without clearance. I called TRACON and explained the situation above. Once I told him that our max deviation was 1.5 dots (meaning we were on the LOC at all times while correcting back to centerline) he was relieved and stated 'ok that's all I need to know.'I have experienced this problem with Airbus Flight Directors before and written them up; and the clearing action is always 'cannot duplicate the error'. Even the [Chief Pilot] said he has experienced this same 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.

Attributes
ACN	1710753
Time
Date	201912
Local Time Of Day	0001-0600
Environment
Flight Conditions	IMC
Aircraft 1
Make Model Name	A300
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types