CANADAIR CL604. DATA DROPOUT ON FMS #1 AND #2. FMS #3 WAS NORMAL. CREW WAS WORKING AN AIR DATA COMPUTER FAILURE WHEN CTLR NOTICED OFF COURSE TRACK DEV. FMS #1 AND #2 HAD DROPPED FLT PLAN INFO AND WAS PROCEEDING DIRECT TO A WAYPOINT SEVERAL WAYPOINTS AHEAD.

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ACFT ON FLT FROM SFO TO MDW ON MAY/XA/98. WE FILED MVA; J84. CLRNC GAVE LIN J84 MVA AS FILED. WE RE-ENTERED FLT PLAN INTO MSA #1 AND #2. APPARENTLY; WHEN RE-ENTERING; SOME DATA GOT DELETED ON THE AIRWAY. AFTER XING MVA AT XA11Z; THE FMS #1 AND #2 PICKED UP A DIRECT OBH ROUTING WHICH PUT US SOME 11 MI N OF THE AIRWAY. PRIOR TO REACHING RESTR AREA R6405 WHICH WAS HOT; ATC ASKED US IF WE WERE ON A HDG ASSIGNED. WE LOOKED AT THE FMS'S AND INFORMED HIM WE WERE DIRECT OBH. HE SAID HE WAS NOT AWARE OF THAT AND GAVE US A 15 DEG R VECTOR FOR A FEW MINS TO AVOID R6405 AND THEN RECLRED US DIRECT TO OBH. THE FMS #3 WAS INDICATING THE PROPER J84 THE WHOLE TIME. OUR FIRST ERROR WAS DATA ENTRY AND CONFIRMATION DURING THE RERTE. THE SECOND ERROR WAS NOT PROPERLY MONITORING THE PROGRESS ON ALL FMS'S. THIS LATTER ERROR WAS MADE DURING A PERIOD IN WHICH WE HAD EXPERIENCED AN AIR DATA COMPUTER FAILURE AND WE WERE INVOLVED WITH CHKLIST ITEMS AND PHONE CALLS TO MAINT OPS AND DISPATCH TO DISCUSS POSSIBLE OPTIONS. AFTER THE CTLR ASSIGNED US THE HDG; WE XCHKED THE FMS #1; #2 AND #3 WITH FLT PLAN AND DISCOVERED OUR ERROR.