Narrative:

Aircraft was dispatched with #1 FMGC and autoplt inoperative. During descent flight was given restr to cross holey at 11000 ft. While descending through 20000 ft on a minimum power descent (FMGS managed), #2 FMGC failed resulting in complete loss of managed navigation, loss of monitored vors, autoplt, automatic thrust (thrust lock), all pictorial navigation. Using rmp (radio management panel) crew manually tuned VOR and selected course. Upon confirmation of VOR, we found we had missed holey intersection crossing by 1200 ft. Note: we had no way of knowing our position with respect to VOR since FMGC normally controls vors, and absent of FMGC, there is no position information displayed or available. After leveling, we were able to restore FMGC #2 and were required to reload all data into FMGC. Only IRS position information was available when FMGC #2 came on line. We eventually recovered autoplt, automatic thrust and FMGC for duration of flight. The loss of both FMGC's, however remote, occurred. Crew actions were appropriate for conditions and there was no conflict at any time. With the advanced automation in the A320, complete loss of navigation becomes a serious problem, since it impacts not only navigation, but also autoplt, and automatic thrust as well, creating a high workload on crew, especially in a descent. Airbus states that the automation should make 1 plus 1 equal 3. (Being 2 crew members plus autoflt.) this was a case where 1 plus 1 equaled 0. Callback conversation with reporter revealed the following information: according to the reporter, the major discrepancy which came to light as a result of this incident is, there is no provision in the MEL's for a failed FMGC (flight mgmt guidance computer). The only maintenance item deferred, in case of FMGC fail, is the associated autoplt. Consequently, the only clue the pilots have of the FMGC failure is the message on the navigation display, 'set offside rng/mode,' and on the pfd (primary flight display) FMA (flight mode annunciator). In this case, with the #1 FMGC failed the #1 and #2 FMA's showed '2fd2' which tells the pilots that only the #2 flight director is available. During the descent with failure of the #2 FMGC, both navigation displays went blank, autoplt disengaged, autothrottles froze in position with the pfd mode annunciator message 'thr lk' (flashing amber), and loss of all navigation radios. Captain reporter turned the aircraft control over to the first officer while he selected manual VOR and succeeded tuning the rbv VOR on the ward 4 arrival to ewr. But, due to the time delay and loss of navigation, the crossing restr at holey was not met. ATC made no mention. Then, the #2 FMGC came back on the line with all subsys operating normally. Post flight maintenance check revealed no discrepancy. On the next leg reporter says they were on approach, in area of thunderstorms, when again the #2 FMGC failed. The flight crew was more prepared then and immediately manually tuned the ILS frequency for the approach. During the approach, however, the #2 ILS (now on the captain navigation display) was intermittent, but the first officer's was normal. After intercepting the ILS it was very unreliable. Aircraft broke out of WX at 2000 ft and continued visually. After touchdown the first officer lost the ILS #1. Reporter says that several issues need to be addressed: 1) when an FMGC is inoperative or intermittent, include it in the MEL and pull the associated circuit breaker to eliminate spurious signals. 2) postflt maintenance printout (centralized data fault display system, cfds) should be reviewed by the pilots with maintenance. It would educate the pilots concerning faults which occurred on their flight. Not only does it include all the faults or failures, but also lists them in real time. Thus, the pilots can learn why and when subsys fail. 3) pilots should be exposed to these type of failure sits during training in order to be better prepared.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB -- BOTH FMGC FAIL XING RESTR NOT MET.

Narrative: ACFT WAS DISPATCHED WITH #1 FMGC AND AUTOPLT INOP. DURING DSCNT FLT WAS GIVEN RESTR TO CROSS HOLEY AT 11000 FT. WHILE DSNDING THROUGH 20000 FT ON A MINIMUM PWR DSCNT (FMGS MANAGED), #2 FMGC FAILED RESULTING IN COMPLETE LOSS OF MANAGED NAV, LOSS OF MONITORED VORS, AUTOPLT, AUTO THRUST (THRUST LOCK), ALL PICTORIAL NAV. USING RMP (RADIO MGMNT PANEL) CREW MANUALLY TUNED VOR AND SELECTED COURSE. UPON CONFIRMATION OF VOR, WE FOUND WE HAD MISSED HOLEY INTXN XING BY 1200 FT. NOTE: WE HAD NO WAY OF KNOWING OUR POS WITH RESPECT TO VOR SINCE FMGC NORMALLY CTLS VORS, AND ABSENT OF FMGC, THERE IS NO POS INFO DISPLAYED OR AVAILABLE. AFTER LEVELING, WE WERE ABLE TO RESTORE FMGC #2 AND WERE REQUIRED TO RELOAD ALL DATA INTO FMGC. ONLY IRS POS INFO WAS AVAILABLE WHEN FMGC #2 CAME ON LINE. WE EVENTUALLY RECOVERED AUTOPLT, AUTO THRUST AND FMGC FOR DURATION OF FLT. THE LOSS OF BOTH FMGC'S, HOWEVER REMOTE, OCCURRED. CREW ACTIONS WERE APPROPRIATE FOR CONDITIONS AND THERE WAS NO CONFLICT AT ANY TIME. WITH THE ADVANCED AUTOMATION IN THE A320, COMPLETE LOSS OF NAV BECOMES A SERIOUS PROB, SINCE IT IMPACTS NOT ONLY NAV, BUT ALSO AUTOPLT, AND AUTO THRUST AS WELL, CREATING A HIGH WORKLOAD ON CREW, ESPECIALLY IN A DSCNT. AIRBUS STATES THAT THE AUTOMATION SHOULD MAKE 1 PLUS 1 EQUAL 3. (BEING 2 CREW MEMBERS PLUS AUTOFLT.) THIS WAS A CASE WHERE 1 PLUS 1 EQUALED 0. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ACCORDING TO THE RPTR, THE MAJOR DISCREPANCY WHICH CAME TO LIGHT AS A RESULT OF THIS INCIDENT IS, THERE IS NO PROVISION IN THE MEL'S FOR A FAILED FMGC (FLT MGMT GUIDANCE COMPUTER). THE ONLY MAINT ITEM DEFERRED, IN CASE OF FMGC FAIL, IS THE ASSOCIATED AUTOPLT. CONSEQUENTLY, THE ONLY CLUE THE PLTS HAVE OF THE FMGC FAILURE IS THE MESSAGE ON THE NAV DISPLAY, 'SET OFFSIDE RNG/MODE,' AND ON THE PFD (PRIMARY FLT DISPLAY) FMA (FLT MODE ANNUNCIATOR). IN THIS CASE, WITH THE #1 FMGC FAILED THE #1 AND #2 FMA'S SHOWED '2FD2' WHICH TELLS THE PLTS THAT ONLY THE #2 FLT DIRECTOR IS AVAILABLE. DURING THE DSCNT WITH FAILURE OF THE #2 FMGC, BOTH NAV DISPLAYS WENT BLANK, AUTOPLT DISENGAGED, AUTOTHROTTLES FROZE IN POS WITH THE PFD MODE ANNUNCIATOR MESSAGE 'THR LK' (FLASHING AMBER), AND LOSS OF ALL NAV RADIOS. CAPT RPTR TURNED THE ACFT CTL OVER TO THE FO WHILE HE SELECTED MANUAL VOR AND SUCCEEDED TUNING THE RBV VOR ON THE WARD 4 ARR TO EWR. BUT, DUE TO THE TIME DELAY AND LOSS OF NAV, THE XING RESTR AT HOLEY WAS NOT MET. ATC MADE NO MENTION. THEN, THE #2 FMGC CAME BACK ON THE LINE WITH ALL SUBSYS OPERATING NORMALLY. POST FLT MAINT CHK REVEALED NO DISCREPANCY. ON THE NEXT LEG RPTR SAYS THEY WERE ON APCH, IN AREA OF TSTMS, WHEN AGAIN THE #2 FMGC FAILED. THE FLC WAS MORE PREPARED THEN AND IMMEDIATELY MANUALLY TUNED THE ILS FREQ FOR THE APCH. DURING THE APCH, HOWEVER, THE #2 ILS (NOW ON THE CAPT NAV DISPLAY) WAS INTERMITTENT, BUT THE FO'S WAS NORMAL. AFTER INTERCEPTING THE ILS IT WAS VERY UNRELIABLE. ACFT BROKE OUT OF WX AT 2000 FT AND CONTINUED VISUALLY. AFTER TOUCHDOWN THE FO LOST THE ILS #1. RPTR SAYS THAT SEVERAL ISSUES NEED TO BE ADDRESSED: 1) WHEN AN FMGC IS INOP OR INTERMITTENT, INCLUDE IT IN THE MEL AND PULL THE ASSOCIATED CIRCUIT BREAKER TO ELIMINATE SPURIOUS SIGNALS. 2) POSTFLT MAINT PRINTOUT (CENTRALIZED DATA FAULT DISPLAY SYS, CFDS) SHOULD BE REVIEWED BY THE PLTS WITH MAINT. IT WOULD EDUCATE THE PLTS CONCERNING FAULTS WHICH OCCURRED ON THEIR FLT. NOT ONLY DOES IT INCLUDE ALL THE FAULTS OR FAILURES, BUT ALSO LISTS THEM IN REAL TIME. THUS, THE PLTS CAN LEARN WHY AND WHEN SUBSYS FAIL. 3) PLTS SHOULD BE EXPOSED TO THESE TYPE OF FAILURE SITS DURING TRAINING IN ORDER TO BE BETTER PREPARED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.