Date: 202104
Local time of day: 0001-0600
Location: ZZZZ.Tower, FO
Flight conditions: Marginal
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Approach
ATC / advisory: Center ZZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Workload; Situational Awareness; Physiological - Other; Fatigue; Confusion; Communication Breakdown
Second reporter function: First Officer; Pilot Flying
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Ground Event / Encounter Ground Equipment Issue
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Contributing factors: Human Factors; Weather
Primary problem: Human Factors

Narrative: Intercepting the unstable Localizer on a 225 vector; approximately 16 nm final; the aircraft started to join the Localizer. The Localizer shifted to the right and the aircraft began a hard right turn to intercept passing of approximately 240 degrees. I instructed the FO to stop the turn and come back to the left toward final approach heading.  He did not reply to my direction and did not act.  As the aircraft passed approximately 255 degrees; I took command of the aircraft; disconnected the auto-pilot and started a turn back to the Localizer.  I was concerned about the numerous aircraft on final for Runway XX.  In my turn back to the Localizer I overshot the Localizer and deviated from the assigned 900 meter altitude by approximately 100 meters.  I intercepted the Localizer; got back on altitude; and flew an uneventful ILS and normal landing. This all happened unexpectedly. The hard right-hand turn to intercept is unprecedented in my XX years of flying [this type aircraft].Unstable Localizer and Autopilot aggressive turn to intercept. Fatigue affected my flying after taking the aircraftThe current schedules to service this country during Covid leave no extra margin of safety when things like this go wrong. Multi-leg days; with long turns between flights; after crossing X time zones leave little margin of safety. Also; the very long trip extensions for crew members leads to fatigue.


Second narrative: I was the PF for the 2nd leg of the night which was a night recovery.  At altitude I had briefed the STAR and approach; and once the descent started; we received numerous altitude; heading; and airspeed clearances as the controller was trying to work what appeared to be a fairly large recovery into ZZZZ [Airport].  ATIS reported that simultaneous ILS approaches were being flown to [Runway] XXL as well as [Runway] YY.  Approaching ZZZZ; we were being vectored for the ILS Y; Runway XXL and at about 20 miles were cleared 'heading 215; maintain 180 knots to 8 miles; maintain 900 meters until intercepting the Localizer; report established.'  We were already configured at flaps 15 with the ILS tuned and the approach checklist complete.  The assigned heading provided a comfortable 15 degree cut; but with winds of about 120 at 25 knots at our altitude (overshooting crosswind); and parallel approaches being conducted; with the autopilot still engaged; I was diligently watching the automation.  I pressed the APP/LAND tile and initially the aircraft maintained heading; but after a few seconds; it started making some gentle (level) turns left and right.  Initially these turns were mild and we even chuckled at what a poor job the AP was doing to maintain heading to intercept.  Suddenly; the magnitude of one of the turns to the right increased markedly and the aircraft was in a level turn to the right of approximately 25 degrees angle of bank with the heading coming through approximately 230 degrees.  As I spent just a few seconds (no more than 4 or 5 I would say) trying to determine what the autopilot was doing; the CA called out; 'turn left; turn LEFT; I have the airplane' and executed a maneuver that I would describe as similar to a PRM breakout maneuver.  He disconnected the AP; added power; and reversed our turn; climbing and accelerating in the process.  The maneuver was aggressive enough that I thought it possible the CA had SA to something that I was missing since I had already started to reach for the heading selector in order to get the plane to level its wings and come back to the left (note: things were happening very quickly now and I did not verbalize this FMC input since I would have just been trying to talk over the CA telling me to turn left even though the airplane did start to shallow its turn to the right once I pulled the selector).  I verbalized 'you have the controls' and monitored his inputs.  As former fighter pilots; the CA and I both have fairly wide comfort zones and although the maneuver was fairly aggressive; I was still comfortable with the aircraft's attitude and remained quiet as I monitored the aircraft's flight path.  I did not want to add to the confusion of the moment by asking questions or saying anything unnecessary since the CA was very purposeful in his maneuver.  Now things became quite busy because in addition to receiving a 'bank angle' audible warning due to our steep turn to the left; the approach Controller began talking to us rapidly.  He made several transmissions and told us repeatedly that he had us on a heading that was not going to intercept the Localizer and that we were above our assigned altitude and asked what we were doing. I replied that we were still below the glidepath at approximately 930 meters; and maneuvering to intercept the Localizer.  After a few more moments the CA stabilized the aircraft's attitude; I selected FMS speeds (since we had accelerated to approximately 210 knots and needed to slow back to 180 knots); and he began a turn back to the right to intercept the Localizer.  The CA re-armed the approach (but never re-engaged the AP); slowed to the assigned speed; returned to the assigned altitude; and leveled the wings on an appropriate intercept heading.  The FD provided what appeared to be valid guidance to shoot the rest of the approach.  The aircraft was configured and stable before glide-slope intercept and the remainder of the approach proceeded normally with me remaining in my role as PM.We went from conducting a routine controlled approach; to one where I think we had widely differing perceptions of what was actually occurring in the space of literally about 4 or 5 seconds.  This rapid breakdown of CRM resulted in actions that were perhaps more aggressive than they needed to be; and a deviation from the ATC clearance.  I would actually say there were two separate events.  The first being the aircraft's unexpected and overly aggressive turn to the right to capture the Localizer for ILS Runway XXL; and the second being our response to it.  The first I would potentially attribute to a software issue; a problem with the ILS tune; or some sort of RF interference.  As far as the second I would suggest the following; 1) Even though I did not feel fatigued during the approach; it was at the end of a long day and it's possible I underestimated my level of fatigue.  That said; I did have some coffee prior to Beginning of Daylight (BOD) for this reason and; I felt like the CA and I were both alert and engaged and don't feel like my response to the aircraft was unacceptably slow or inappropriate.  2)The CA believed that the intercept angle was excessive (he referenced 45 degrees during our debrief) and that based on his prior experiences; there was no way the airplane was going to be able to capture the Localizer.  Since I had not experienced the automation act in the manner it did during our approach; I was perhaps more comfortable than I should have been with the AP's ability to capture the Localizer; even with the admittedly substantial intercept angle that we had before the CA took the controls.  3)  The CA stated during the debrief that he thought we had already flown through the Localizer; and that he was therefore worried about a lack of separation from the traffic that was flying the ILS to Runway XX; to our right.  I did not perceive that we had flown through the Localizer for the following reasons: a) We were in a phase of flight where we both (certainly I was) monitoring the raw Localizer data in anticipation of Localizer capture; and neither of us ever called 'Localizer alive'.  I felt like I was hawking this for the reasons listed above (overshooting crosswind and proximity to other landing traffic). b) The AP commanded a turn to the right; which in my mind it would have only done if it were trying to intercept the Localizer from the left.  c) When ATC contacted us; it was to say that we were not on an intercept heading.  He did not indicate that we had flown through the Localizer or were encroaching on the protected airspace between the approach corridors for the active runways. He never issued a vector to East which is likely what he would have done had he perceived there to be a risk of loss of separation.  d) When we finally got the situation under control; the aircraft intercepted the Localizer from the left.Again; this entire narrative took place in what I suspect was less than a minute.  Between the uncommanded turn to the right and the CA taking the controls; maybe 5 seconds passed.  That said; I could have acted sooner and certainly should have verbalized when I reached for the heading selector to stabilize the heading; since that may have precluded the CA from taking the controls and executing the 'escape' maneuver.  I think in the CA's mind; we were probably already past the point where that was going to mitigate our situation since he perceived that we had already crossed the Localizer; but it might have helped.  I wish the CA would have verbalized why he was maneuvering as aggressively as he was.  I thought that perhaps he saw an impending collision that I did not have SA of; and so I stayed quiet for longer than I should have before I started to rebuild the picture and work to develop a CRM.  Ultimately; he was well within his authority to act in the manner he did and fully adhered to the company's three step intervention process.   This was a tough one for me to analyze and I welcome any feedback you might have.


Synopsis: Air carrier flight crew reported an altitude and track heading deviation during approach to an international airport.  The crew stated this sequence of flights; since the COVID-19 pandemic started; are very long and fatiguing which may have been a factor in the event.