A320
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 270; Flight Crew Total 18000; Flight Crew Type 2500
Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types
Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
While approaching CLE; the Airbus I was flying experienced a simultaneous dual FMS failure but at the time; thought it was a spurious fluke. Last night while approaching SEA I had another simultaneous dual FMS failure. After landing the FO told me he had recently seen the exact same thing. When briefing the Captain who was taking the aircraft out of SEA; he told me that he too had experienced a recent dual FMS failure; and that he had just flown with another FO who had experienced two of them. From these discussions; I learned that all of these happened at the exact same point in the flight; when? Cleaning up the box? After being vectored off of the arrival STAR. For at least a year I have frequently used the technique of selecting 'No Star' under 'Arrivals' after being vectored off of the STAR. This would result in the box automatically entering all of the fixes on the loaded approach; along with the crossing altitudes. This saves a lot of time in the approach environment; and is useful at time such as when ORD TRACON vectors you off one of the southeast arrivals with a turn to intercept the 27L ILS; which has multiple step-downs which must be complied with. In the case of my two FMS failures; I had just entered 'No Star.' I noticed that the fixes on the ILS did not automatically load as I have seen in my previous experience. I then attempted to clear out the remaining waypoints from the STAR we had just been vectored off of. That is when both boxes failed simultaneously. 'No Map' was displayed on the ND's; initially the FMS froze and would not respond to any input; then everything was dumped and the orange FMS-1 (and FMS-2 respectively) came on each box. This also causes the pressurization system to lose its landing field elevation value requiring manual over-ride. Also; the landing ref airspeed dumps too. The outbound Captain I spoke with last night said that he does not use the 'No Star' technique I described above; but that his FMS failure did occur when he went to 'clean up the box' after being vectored off of a STAR. I would suggest that someone look into whether there is some systemic issue with a recent data-base update or software change to our FMS's. I know I'm preaching to the choir; but this type of failure occurs at a very inopportune time in the flight. I was fortunate in that both of the failures I experienced occurred in VMC. Had we been IMC we definitely would have had to perform a go-around as it takes a bit of time to get an ILS hard-tuned with an inbound course in Rad-Nav and selected on Rose-ILS; and the pressurization issue has to be dealt with too. It's not a good situation.
The reporter's research indicates that other methods of cleaning up the approach can cause the dual FMGC failures and that the failures seem limited to arrivals to SEA and CLE only. His company is currently working on the issue.
Another A320 Captain experiences the loss of both FMGC's during approach when the 'no star' function is used to clean up the approach after being vectored off an arrival.