A319 flight crew reported temporary loss of aircraft control when the autopilot and autothrottle disengaged during approach; resulting in a course deviation and airborne conflict.
Synopsis
A319 flight crew reported temporary loss of aircraft control when the autopilot and autothrottle disengaged during approach; resulting in a course deviation and airborne conflict.
Narrative
We had 4 legs with this same aircraft on the day of the incident. All day; it had been acting strange; and we were watching it closely after several minor FMS 'glitches' left us guessing as to why the aircraft was doing the things it was doing (mostly to airspeeds and approaches). We never felt the aircraft was dangerous; and the weather everywhere was clear and uneventful; so we kept with it; but agreed we'd 'trust but verify' the aircraft automation; as we were getting no real faults or ECAS messages concerning any aircraft systems. Going into ZZZ1 earlier that day; the aircraft failed to capture the RNAV final and flew through the course. We intervened; corrected; and landed uneventfully. We thought we had maybe done something wrong in the FMS; but we figured we corrected the situation; trapped the error; and landed uneventfully in ZZZ1. We didn't give it much thought afterwards. On one other leg; it failed to go into approach mode at the 'Circle D' on the screen while in the NAV mode and on course. We had to go into the FMS and manually select 'Activate and Confirm' after crossing the 'Circle D'. The last leg into ZZZ was the one that got us in trouble.Weather: ClearWinds: minimalVectors to final; Rnwy XXL; with simultaneous approaches being flown to Rnwy XYCA was PF during this approach.FMS was setup well beforehand; and Rnwy centerline extension was executed and we were on a Heading to final. The aircraft was at 190 IAS; flaps 1 and stable. We were told to intercept final on Rnwy XXL; and armed the LOC. Our flight plan anchor point was in front of us; so the approach would sequence properly. Everything was normal until this point. Upon reaching the point where the aircraft should have intercepted the XXL LOC; it didn't. Our first indication was a query from ATC telling us it looked like we were flying through the course. This surprised us; and we took it out of the LOC mode to make corrections to final. Looking at our displays; the old CRT screens in the A319 showed that we were just about to intercept final; not flying through it. The screens then 'jumped' a small bit; and then we received the initial TCAS TA. After flying through the course; and while attempting to correct our position; the TCAS TA was followed quickly by an RA from an aircraft on the parallel approach for Rnwy XY. I had already started to take action before the TCAS RA; and started turning with the autopilot engaged to the final approach course as I noticed our aircraft encroaching upon the northern runway approach path; and failing to capture final. After the RA the aircraft Autopilot and Autothrust were disengaged and I had to steeply bank away from the other traffic; and began a climb for our RA. I do not remember disengaging the auto thrust system; but it disengaged. At this point; our stabilized approach was completely gone; and we were fighting for control of the aircraft and our situational awareness and position; trying to keep from overspeeding drag devices; getting too slow; and avoiding the aircraft from our TCAS RA. I do not think we reported that we were responding to an RA. Autothrust would not reengage; and Autopilot was not responding properly to inputted commands; so I disengaged it completely and was hand flying everything. ATC was also calling us repeatedly as we fought for aircraft control. I instructed my FO to respond to their 'state intentions' queries; and to tell them to break us out of the approach; and that we were having systems malfunctions. ATC seemed to want us to continue the approach; and we were not in a safe or stable condition to do so. Both myself and my FO were extremely task-saturated; and we did not state 'pan pan' to declare an emergency; only that we were having trouble controlling the aircraft; and automation seemed to be fighting us when we tried to engage it. It's all we could manage saying with everything we were going through. Shock and surprise factors were definitely in full effect. Everything was good right up until it all wasn't.ATC vectored us back around; and sequenced us back into the Rnwy XXL flow. I was able to get the AP reengaged for a portion or the downwind and approach. Once we were starting our final descent; I disengaged the AP entirely due to our lack of confidence in it; and I hand flew the entire segment without AP or AT. The rest of the approach and landing were uneventful. We did hear on the radio that there were other aircraft that were having issues intercepting final as well; though none sounded as serious as ours; and I didn't hear full details; as we were focused on just safely getting our aircraft on the ground. After switching over to ZZZ GRND control; we were given a 'possible pilot deviation' and a number to call. After parking; shutting down; and completing checklists; I called ZZZ tower at the supplied number. The Controller was very professional as I explained what happened to us on the approach. I passed my information to him; and he shared with me that this was becoming a common occurrence in ZZZ; and that there were probable systems issues with the approach equipment at ZZZ; and that they were on a fact finding mission to resolve those issues similar to ours. I'm not sure if that was a direct cause in our case; but combined with the issues our aircraft was having; could have combined to create the incident we experienced.I was very rattled after this incident. I've flown the A320 series aircraft for X years as an FO; and almost X.Y years as a CA. I'm very comfortable with; and knowledgeable about the aircraft. I've never had one not respond and get away from me the way this one did. It took both pilots everything we had to balance not over speeding the drag devices; and not getting too slow while we tried to figure out just why the aircraft was not responding as expected; while simultaneously hand flying and attempting to avoid other aircraft on the parallel approach. I felt we were both dangerously task saturated; but we somehow managed to pull everything back together just enough to put us back into a safe operating zone and get the aircraft safely on the ground.I do not have any recommendations at this time; as I still don't fully understand what happened with the aircraft. I made a Maintenance write-up on this aircraft; and the logbook deferral sheet was promptly signed off by maintenance and returned to service by the time we left the airport for our short layover in ZZZ. The action was the 'MMR (Multi-Mode Receiver) was reset and ops checked good'. Another crew accepted it and it proceeded to ZZZ2 shortly afterwards.
Second reporter narrative
We had this aircraft all day and it was doing a lot of weird things to us all day. We had situation where we passed circle D and the approach did not arm. Another situation where I had 290 knots preselected in the FMS and Managed Speed. The plane just decide to go to 250 knots on the speed. We did not pass circle D and not even close to 10k feet; we was at 16k on the altitude when it happened. During our RNAV approach into ZZZ1 airport the inbound course did not capture. During this ILS approach I was very tentative to the PFD because of past experience with other aircraft. I flew corporate; so I had many years of experience staying with the same aircraft. When an aircraft starts acting up it gets worse through the course of the day and this was the fourth and final leg of the day. I was literally staring at the PFD when I saw that we was going to capture the LOC and GS about the same time and then everything dropped out right at capture/active phase. The WOW factor kicked in and I couldn't figure out what happened. I had no idea that the auto pilot kicked off until the Captain said something. He later told me that the AutoThrottle kicked off too. I was in shocked as I have never experienced something like that. At that exact time we then get the RA; and simultaneously being informed by ATC that we blew by the localizer. We started to correct and requested to be re-vectored for the approach. I had to request twice because it seemed like she wanted us to continue the approach. We received our instructions and landed the aircraft without further incident.My suggestions are that planes that have incidents like this should be taken out of service. the 'can not duplicate' factor should not be used. The planes should re-download new software. In my other life when this happened to my Corporate Plane; I would fly it to the manufacturer's maintenance and have them upload the software again and that would always take care of the issue.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.