Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Workload; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Regained Aircraft Control; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem; General Maintenance Action
Human Factors; Aircraft
During the climb out of ZZZZ we got a Master Caution '>Autopilot' on the EICAS. At the time the right autopilot was connected; and in LNAV and VNAV modes. There was no autopilot disconnect; and there were no FMA mode flags. We noted the issue; looked at what the QRH had to say; and continued. We decided that the best thing to do was monitor the situation.We leveled at 8000 ft. and began getting 'direct to' clearances that shorten the distance from ZZZZ to ZZZZ1. We had begun a descent that put us in a good position to land in ZZZZ1; but then our route was cut much shorter than anticipated. We were cleared to descend to 3000 ft. on a heading of 220. I had called for flaps 5; and had the speed brakes extended in FLCH mode to help get us down a little quicker. The speed bug was down between Vref for flaps 1 and 5 with the flaps extended (not in transit) to Flaps 5. Passing about 4500 ft. in the turn to heading 220 we were given further turn to 280; and cleared for the ILS approach. We do not have a chart for the ILS approach to that runway and were shooting a VFR approach; and the Captain was stating this to the controller to get a clearance for the visual approach - consistent with the limited information available for this airport in [software].I was looking at the heading window; dialing heading 280 when the Captain called out that we were approaching a speed that would overspeed the flaps. I stopped; looked at the PFD (Primary Flight Display) to assess the situation that had suddenly developed; and my first impulse was to change the vertical mode to V/S to shallow the descent in order to slow the airplane; in the 1-2 seconds that I had moved my hand to carry out that change the Captain began saying 'Pull up! Pull up! Disconnect the autopilot and pull up!' I looked back at the PFD; saw that we were at the high speed cue; and descending through 3000 ft. The Flight Director had captured the altitude. 'ALT' was displayed on the FMA. There were no FMA mode flags. It appeared that the autopilot had stopped following the Flight Director guidance; and may have pitched down further. I disconnected the autopilot and recovered the aircraft to straight and level flight as quickly as I felt I could without over stressing the wing. We had descended to roughly 2300 ft. Throughout the recovery the Flight Director showed guidance to maintain 3000 ft.There was some discussion as to whether we should attempt to climb back to 3000; or continue the approach from our present position. At 2300 ft. we were just slightly low on the approach. We were established on our straight-in course to the runway; and I had heard cleared for the approach at some point in the preceding few seconds. We confirmed our approach clearance; and continued the approach to a landing at ZZZZ1.Once we shut down the aircraft we wrote up the autopilot as not functioning correctly because it failed to follow the Flight Director guidance. We could find no reason why it would've stopped following the Flight Director guidance prior to the event; and believed that the autopilot malfunction was the cause of the event.This event highlights how rapidly a situation can develop. The only times my eyes were off the PFD were when I had them on the Mode Control Panel to control the autopilot. What I saw on the PFD when I looked back had me believing I must have been distracted for a significant time for this to develop; but I know that is not true. It developed within just a couple of seconds; and this was confirmed by the other pilots who didn't believe that I had missed anything.The situation got to the point that it did because of a turn clearance that came at the exact moment that the autopilot stopped following the Flight Director; and it occurred right around the time that we would call 1000 ft. to level off. We all know this 1000 ft. is a critical time; and our crew was paying attention. It highlights that even when we're doing everything right; something canquickly develop.As the pilot flying my mind went into an upset recovery mode for a few moments. The aircraft attitude was not outside the normal pitch or roll limitations; but I saw and treated this as a recovery in which I temporarily ignored route and altitude clearances until I was confident the plane was recovered to straight and level. This mentality was not easy to leave as we continued to the landing. In the future I will probably ask that we discontinue the approach for a few moments to ensure everyone in the cockpit (including myself) is ready to continue to the landing. To be roughly on glide path at 2300 ft. meant that when we recovered and continued to landing we were at least nearing an 8 mile final; and because of the issue we had to continue to move with purpose to continue that approach from a Flaps 5 configuration to being stable and configured at 1000 ft. Taking a moment to slow the tempo down after that event would've been a better course to take.
On climb out just before level off at 8000 ft. (short flight; final cruise altitude) we received an 'auto pilot' caution message. I was the Pilot Monitoring and we went over the QRH (advisory QRH; no action) The Pilot Flying was advised that per QRH the Autopilot was working at degraded mode. The autopilot seems to work properly tracking L nav and leveling off at 8000 ft. and holding altitude properly. I asked the Pilot Flying to pay extra attention to the autopilot. Shortly afterward; we were descending to 3000 (FLCh mode) and on a turn towards the airport for visual approach. At 3000 ft. I called altitude and airspeed. I noticed [the] airplane wasn't leveling and airspeed actually accelerating towards flaps 5 limits. I called the Pilot Flying to disconnect the autopilot and pitch up to return to altitude and to prevent flaps over speed. We recovered around 2600 ft. and climbed back to 3000 ft. without exceeding AFM limitation (G loads and flaps over speed).We continue to [our] destination for a visual approach followed by a normal approach and landing. At the gate we entered [the] discrepancy in [the] aircraft logbook. Maintenance could not duplicate issues after test and diagnostic.This was a short flight with [a] high workload and ATC barrier. Even though this was a high workload environment. As a crew; we should have disconnected the autopilot and hand flown the airplane or use another autopilot. Pilot flying should have paid more attention to the airplane and so should have I (Pilot Monitoring).I hope we can add a note in the QRH to try and connect [the] other autopilot even if the current one looks like it's doing a good job.
B747-400 flight crew reported continuing to use an autopilot after it had previously triggered an EICAS warning resulting in altitude and heading clearance deviations.