Date: 201201
Local time of day: 1801-2400
Location: ZDV.ARTCC, CO
Weather elements / visibility: Turbulence
Light: Night
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Aircraft component: FMS/FMC
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Confusion; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Early in the Cruise Phase; First Officer was pilot flying. It was brought to my attention by the First Officer that his ND was displaying 'Map Not Available' in red color; no map was displayed on the number 2 ND. Seconds later a level 2 ECAM (single chime) with the message of CAB PR LDG ELEV FAULT; which was then accompanied by another fault; the lower ECAM GW display was amber XX LBS. As the pilot not flying I began to troubleshoot what seemed to be the most critical aspect of the multiple failures. At the time it seemed that the Cabin Pressurization was the most critical; not to mention; it was that problem that triggered the Level 2 caution. Once I determined that the integrity of the pressurization system was not compromised; I moved on to the other issue; the lack of the map display on the First Officer side. It seemed that the number 2 FMGC had failed; however; the PFD indications were consistent with no failures. FMA's displayed MACH ALT CRZ NAV all in green; no mode reversions had occurred. Even the FD mode was 1FD2. Yet; as I scanned over to my display; I realized the aircraft failed to make a turn upon passing the previous fix so I immediately went to HEADING Mode turning the aircraft back to re-intercept the course and engage AP1. The deviation was 6.1 NM left of course. At that moment; ATC had queried our position and asked what our next FIX was; I told ATC what our next fix was. I then requested DIRECT; and was cleared direct. This lateral deviation would have been avoided had the aircraft been equipped with a lateral deviation alert similar to altitude deviation alerts that most aircraft are equipped with. Although flying the airplane is the priority at all times; it was very deceiving to the pilots when the aircraft indicated that it is flying based on what the PFD FMA's were displaying. As a former instructor on this airplane; I always used to tell my students to believe what the FMA displays. In this case; it lied about its NAV capability; even though it displayed a normal green NAV display; it wasn't. There must be a communication link between the ND and the PFD.

Callback: The Reporter stated that the disparity between the green FMA status indications and the FMGC failure to correctly guide the autopilot could not be reconciled. The FMGC faults should have triggered a transition to the default heading mode along with an appropriate FMA change. The only indication the crew saw; other than the ECAM; was the ND2's MAP display fault and on further investigation both FMGC's displayed amber INDEPENDENT OPERATION in small letters at the bottom of the screen. The autopilot was selected to number one and functioned normally to landing. All systems were operating normally even with the FMGC anomalies. After landing the systems reset and operated normally.



Synopsis: An A320 number 2 ND MAP failed and the autopilot did not track correctly causing a track deviation although the FMA indications remained green and the FMGCs entered independent operations.