MD-11
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human-Machine Interface; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented
Aircraft
Approaching ZZZZ VOR; I observed the aircraft position to be on the magenta course line. I observed the aircraft begin a left turn to join ZZZZZ. My map range was 80nm mid-range (160nm full scope). I went about usual cockpit duties. A min or two after the turn was completed; wings level; ATC called to confirm our course; which drew both pilot's attention to examine our indicated position.I found the aircraft position was now right of the magenta line with a 7nm right deviation data tag; the FMAs showed all white: speed defaulted to speed select; Bow Tie; the nav was in HEADING mode; the altitude was LEVEL CHANGE altitude hold; no VOR bearing indicators were visible. I immediately used the heading selector to set a 45 deg intercept; and attempted to reselect NAV mode. Each time I selected NAV; the aircraft rolled out and/or rolled into a right turn after wings level intercept was established. ATC re-cleared us direct ZZZZZ1. The PM (Pilot Monitoring) selected ZZZZZ1; I confirmed it; and that nav was available; then selected NAV. This time the automation tracked the magenta course to ZZZZZ1. I'm not sure if I changed the autopilot from AP2 to AP1 before or after the navigational automation began properly tracking direct ZZZZZ1. At this point; I reselected FMS SPEED and PROF which appeared to work normally.After the automation was fully engaged; I manually tuned ZZZZ VOR which gave us bearing and distance from ZZZZ to verify our position with a ground based navaid. When I cleared the manual tuning; the bearing pointers disappeared; again. I reviewed both sensor status pages and position pages and found no discrepancies. There were no Level 1 or Level 2 alerts annunciations and both MCDU and FMC's did not indicated any abnormalities. After passing the first abeam point; the VOR bearing pointers were displayed started operating normally. There was no cockpit indication noted by PF (Pilot Flying) or PM of any navigational error prior to being queried by ATC. We did advise ATC that an equipment malfunction caused the discrepancy and that we were able to take the necessary actions to overcome the malfunction. But after a lengthy review of the navigational equipment and automation; it appears the malfunction was transient.The Captain was on his rest period and was alerted to the issue. No further requests or inquiries were made by ATC related to the navigational error.The only other thing I noted about 45 min earlier; after climbing from FL350 to FL370; the FMS never re-calculated and Optimal FL. However; it did calculate a MAX FL of 390.Upon returning from my rest period; I learned from the Captain same malfunction occurred two more times; subsequent to the aforementioned event in which ATC was involved.Upon landing we made [a maintenance logbooks] entry.Review / fix XYZ load in MD-11 FMS. The Captain recalled several events in which this has happened to him since XYZ software was loaded in FMS. I will bring the FMA into my crosscheck after each waypoint turn; however that is a human factor burden to correct a design flaw of the current FMS load and is simply not realistic on some routes with large numbers of waypoints in rapid succession. Furthermore; with long distance between waypoints and wings level; the thing could revert to heading mode and drift miles on oceanic legs; even with oceanic procedures that require you to cross check your course; depending on when the malfunction happens.
In normal cruise configuration; all magenta FMS spud; NAV; Hold. Aircraft was tracking correctly for the previous flight and for the first portion of this flight In NAV. The autopilot commenced a turn at point ZZZZ; as [we were switching ATC frequencies]; so it felt like everything was fine as we were indeed in a turn; and I switched up [the next ARTCC]. Evidently somewhere in the turn the auto-flight system reverted to basic mode and came out of NAV reverted to HDG mode; with no alert. It appears we tracked on a heading of about 30 degrees of course for enough time to put us 2-2.5 miles off centerline of [the course]. [ATC] queried our course as both the pilot flying and myself noted the issue. [ARTCC] just gave us direct to ZZZZZ2 and we complied. Controller didn't seem to have an issue with us; and it did not appear we were in conflict with other traffic.[This was caused by] Aircraft system failure coupled with lapse in monitoring.I'm under the impression this malfunction of the FMC system is a known problem with the present XYZ load. I had just gone through three days of training and yet this was not mentioned at all. I feel; that it is important enough and tricky in its presentation; no alerts; that the MD-11 crew force should be made aware of it. That being said pilot monitoring skills were stressed in the current training as well; and at altitude I let my guard down. It could have been worse; I should have been more vigilant.
MD11 flight crew reported autopilot reverted to heading mode uncommanded.