Date: 201409
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: FMS/FMC
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Training / Qualification; Human-Machine Interface; Distraction; Confusion
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action; Flight Crew Became Reoriented; General Maintenance Action
Contributing factors: Procedure; Aircraft; Human Factors
Primary problem: Aircraft

Narrative: We were being vectored for an RNAV visual to Rwy XXL.  The approach loaded in FMGC's was the ILS to Rwy XYL; the FO was the pilot flying; and he attempted to load the RNAV visual into the right FMGC.  When he did this; the entire database dumped.  There was no data in the navigation system whatsoever; and neither of us were able to load a new destination.  I notified the controller that we had lost our navigation system; and we would be unable to shoot the RNAV visual.  Since the weather was VMC and no clouds; with >10 visibility; I asked the FO if he would be OK to get vectors to a visual approach.  He said he was fine with that; and I asked the controller for vectors.  The controller asked us if we needed special assistance; and I advised him that we did not; but we only had basic instruments.  He told us that he would vector us toward ZZZ VOR; and then we could tell him when we had the airport in sight.  We proceeded with the vectors; and visually acquired the airport.  It was during this time that the FO spent a good deal of time heads down; and that lead to some distractions.  I too was distracted by the malfunction; and spend a good deal of time heads down.  I noticed that the APP Mode was not armed at about 7;000 MSL.  The FO asked me to arm it then; and I pushed the button to arm it; but was then again distracted by a question from ATC; and I failed to press the CONFIRM button.  APP Mode was not armed; and at 3;000' when the FO pressed the speed button to go 'managed' on the speed; the power and target speed went to 250 knots.  The FO; not realizing that this problem was a normal result of APP mode not being selected; disconnected the auto-thrust; and proceeded to fly the visual approach with manual thrust control.  He believed that he could not trust the auto-throttles; although the FMCG problem was apparently unrelated to the speed issue of not being in APP mode when selecting managed speed.  This additional attention to detail of flying the visual approach in manual thrust mode causes us to be high on glide-path as the FO started to fly erroneous flight director indications.  I turned off the flight directors to prevent him from being confused by the FD.  The FO corrected the aircraft onto the glide-path; however we became destabilized for a brief period below 500'; and the FO got the rate of descent to around 1;200 FPM at 400'.  We landed uneventfully. This data dump of the FMGC's concerns me because it could present be a serious problem if in IMC and minimal fuel.  We had enough extra fuel to make the go around; so I would recommend going around early next time as soon as the FO and I were not on the same page as to the use of the manual thrust; and the FO was not comfortable flying in manual thrust.  I would suggest that we practice more manual thrust visual approaches in the simulator during our recurrent training.  I should have been more active in telling the FO not to go heads down once we were in the later stages of being vectored for a visual approach.  His continued efforts to figure out how to reload the database were not helpful at that point in the flight; and our goal for a stable approach would have been better served if he had stayed outside and not been working on the FMGC.  Had we wanted to work on the FMGC at that late stage; we would have needed to ask for a heading or a holding pattern.  I think our plan to land with a visual was a good plan; but once we committed to that plan; we should have ceased troubleshooting the FMGC's that low and that close to the airport.  Also; I should have had more attention to detail in not getting distracted from arming the APP mode as that caused the FO to connect unrelated issues of Navigation Failure and Autothrust Failure as there was no Autothrust failure.


Second narrative: The primary and secondary routes on both FMGC's dumped. I was able to reestablish the RNAV Visual XXL Approach by selecting direct to one of the arrival waypoint and then selecting a new destination into the FMGS. Captain ask ATC for a visual approach to XXL to help reduce the work load. We were still being vectored at this point. Captain finished updating the arrival information into the FMGS for me; he also activated the approach. When we were cleared for the visual approach I went direct to the waypoint and started the approach.  I decided to continue with The visual approach. I tried managed speed for the approach but the plane wanted to speed up to 209 knots. I asked him to set the approach speed manually and that I would hand flying. By this point I was controlling the thrust manually; this was to insure we would maintain the proper speed. By this point turning onto final. I realized I was a high and started to correct. At 1000ft I was stable and slightly high; between 1000 and 500 ft I got a GPWS warning for sink. I corrected and landed with no other issues. Captain wrote up the MCDU. The avionics mechanic said that he had seen this before and at the same point in flight; during a runway change input into the MCDU.


Synopsis: An A321 FMGC dumped the primary and secondary routes when the Captain selected an RNAV Visual 13R in the Secondary Flight Plan while the First Officer was flying the VOR 13L in the Primary Flight Plan. They were able to partially recover before landing.