Narrative:

Evening departure out of iad. The clearance was radar vectors hafnr gve sbv. All preflight and operations checks were normal. After takeoff we were assigned radar vectors and eventually direct gve. According to our FMS; gve was about 90 degrees to our right. We challenged ATC stating the turn did not seem correct and we were told by ATC direct gve for now. Direct gve was initiated and the aircraft made a right turn. We challenged ATC several times stating the turn did not look correct to us. ATC told us to continue direct gve. The crew noticed the #1 FMS was no longer in sync with #2 FMS. At about the same instant we noticed traffic at our altitude roughly 7 mi out. We asked ATC if they had that traffic and requested a heading while we looked into our problem. ATC asked us to immediately climb and asked if we were proceeding direct to gve. We immediately initiated the climb (TCAS never alerted). After a short time we were provided radar vectors and questioned if we were direct gve. We advised ATC of our FMS problem after which we were switched to a new frequency and left on vectors. We advised the new controller we had an FMS failure and changed our suffix to /a. We continued the flight without event using raw data. I believe the crew could have persisted on the challenges to ATC differently by advising the heading that direct gve provided. Stated differently; a challenge may have put a question in the controller's thoughts. Also; it was later discussed among the crew that a second mfd in the aircraft may have shown the discrepancy a little earlier. The workload of the controller may have also contributed to the situation by not allowing the controller to give our challenges proper attention. The situation emphasizes the need to back up your navigation sources (we had departed iad VOR and ILS frequency in the box). It also shows the need to maintain good CRM skills and discuss irregularities which occur during flight.

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Original NASA ASRS Text

Title: BE400 FLT CREW ON DEP FROM IAD EXPERIENCED FMS FAILURE; RESULTING IN DEV FROM CLRNC.

Narrative: EVENING DEP OUT OF IAD. THE CLRNC WAS RADAR VECTORS HAFNR GVE SBV. ALL PREFLT AND OPS CHKS WERE NORMAL. AFTER TKOF WE WERE ASSIGNED RADAR VECTORS AND EVENTUALLY DIRECT GVE. ACCORDING TO OUR FMS; GVE WAS ABOUT 90 DEGS TO OUR R. WE CHALLENGED ATC STATING THE TURN DID NOT SEEM CORRECT AND WE WERE TOLD BY ATC DIRECT GVE FOR NOW. DIRECT GVE WAS INITIATED AND THE ACFT MADE A R TURN. WE CHALLENGED ATC SEVERAL TIMES STATING THE TURN DID NOT LOOK CORRECT TO US. ATC TOLD US TO CONTINUE DIRECT GVE. THE CREW NOTICED THE #1 FMS WAS NO LONGER IN SYNC WITH #2 FMS. AT ABOUT THE SAME INSTANT WE NOTICED TFC AT OUR ALT ROUGHLY 7 MI OUT. WE ASKED ATC IF THEY HAD THAT TFC AND REQUESTED A HDG WHILE WE LOOKED INTO OUR PROB. ATC ASKED US TO IMMEDIATELY CLB AND ASKED IF WE WERE PROCEEDING DIRECT TO GVE. WE IMMEDIATELY INITIATED THE CLB (TCAS NEVER ALERTED). AFTER A SHORT TIME WE WERE PROVIDED RADAR VECTORS AND QUESTIONED IF WE WERE DIRECT GVE. WE ADVISED ATC OF OUR FMS PROB AFTER WHICH WE WERE SWITCHED TO A NEW FREQ AND LEFT ON VECTORS. WE ADVISED THE NEW CTLR WE HAD AN FMS FAILURE AND CHANGED OUR SUFFIX TO /A. WE CONTINUED THE FLT WITHOUT EVENT USING RAW DATA. I BELIEVE THE CREW COULD HAVE PERSISTED ON THE CHALLENGES TO ATC DIFFERENTLY BY ADVISING THE HDG THAT DIRECT GVE PROVIDED. STATED DIFFERENTLY; A CHALLENGE MAY HAVE PUT A QUESTION IN THE CTLR'S THOUGHTS. ALSO; IT WAS LATER DISCUSSED AMONG THE CREW THAT A SECOND MFD IN THE ACFT MAY HAVE SHOWN THE DISCREPANCY A LITTLE EARLIER. THE WORKLOAD OF THE CTLR MAY HAVE ALSO CONTRIBUTED TO THE SITUATION BY NOT ALLOWING THE CTLR TO GIVE OUR CHALLENGES PROPER ATTN. THE SITUATION EMPHASIZES THE NEED TO BACK UP YOUR NAV SOURCES (WE HAD DEPARTED IAD VOR AND ILS FREQ IN THE BOX). IT ALSO SHOWS THE NEED TO MAINTAIN GOOD CRM SKILLS AND DISCUSS IRREGULARITIES WHICH OCCUR DURING FLT.

Data retrieved from NASA's ASRS site as of January 2009 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.