Date: 201302
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: B747-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Autoflight System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Training / Qualification; Confusion; Distraction
Second reporter function: Pilot Not Flying; Captain; Relief Pilot
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance; Flight Crew Regained Aircraft Control; Flight Crew FLC Overrode Automation; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While at FL350 we were cleared direct. Upon verification and execution of the direct; the aircraft commenced a 25 to 30 degree left bank away from our direct course with LNAV engaged. Selected Heading Select to correct back on course (heading bug was slightly right of course). Aircraft continued its left turn; not responding to the heading mode. I disconnected the autopilot and turned the aircraft back to our programmed course. Upon disconnecting the autopilot the nose descended as there was more pitch down trim than I suspected for cruise flight. Aircraft quickly descended to [between] 350 [and] 400 FT below our assigned altitude of FL350. Quickly corrected the deviation as ATC asked us to check our altitude. At this point we were back to our assigned altitude and course. Also had a brief TA warning with and aircraft below which indicated 800 FT on the ND. Re-engaged the autopilot once stabilized and proceeded on course. The rest of the flight automation performed reasonably well and we did not encounter this type of problem the rest of the flight. I wrote the event up in the logbook and briefed maintenance upon arrival. I was surprised by the pitch down forces of the aircraft once the autopilot was disconnected. I would suggest leaving the automation on longer to alleviate workload overload at the time.


Second narrative: Captain as pilot flying with First Officer as pilot not flying (first OE leg for First Officer). The crew was cleared direct. The First Officer entered the direct fix in the CDU; there was discussion as to how to confirm if it was correct (it was from my perspective); then Captain commanded execute. The aircraft rolled into a 25-30 degree angle of bank immediately. Captain commanded Heading Select to bring the aircraft back on course. The aircraft continued in a left turn. Captain disconnected the autopilot to hand fly the aircraft back on course. The magenta line was indicating a need to turn back right. During the turn back to course we received a TRAFFIC call; not an RA; to cause more confusion. Captain started an un-commanded descent. I called altitude as we passed approximately 200 feet low. The descent continued to 350-400 FT low. ATC called around 350 FT to inquire as to our alt; we were correcting at that time. The autopilot was re-engaged 350 direct with no further incident. The Relief First Officer was sitting in the center jump seat I; the Relief Captain; was sitting in the left jump seat behind the Captain. Maybe select heading hold vice heading select as well encourage patience when at altitude prior to disengaging the autopilot.


Synopsis: A B747-400 entered an uncommanded 25-30 degree bank after a FMS direct to the next fix selection and when the aircraft did not respond the Captain disengaged the aircraft then lost about 350 FT which triggered a TA from nearby traffic.