Narrative:

The flight departed the gate with all normal preflight operations completed. A ground stop at phl required us to shut down our engines and wait 2 hours on the taxiway. The FMS was checked several times and concurred with the flight plan and clearance. On departing we were required to deviate several times due to severe WX. ATC questioned us saying 'where are you?' and stated that we were not cleared direct to fkn. So we checked the FMS only to find the ccv (cape charles) had dropped out and only fkn was remaining as the next point. Ccv was reprogrammed and we were abeam the fix (15 mi to the west). According to the mechanics, when deviating if you get close to or abeam a fix it will drop out. Evidently that is what happened. Neither of us remember it dropping out. We continued on with the rest of our flight plan and nothing else was ever said by ATC. The following day the FMS was programmed and found to be giving erroneous routes of flight. The mechanics reprogrammed the data once we returned to rdu. We flew three more flts and it seemed to be functioning properly. Callback conversation with reporter revealed the following information: reporter talks about how the waypoint dropped out of the flight plan route and the next waypoint in the flight plan became the active waypoint. Reporter was not certain if the FMS was supposed to work this way, however, some mechanics on the subsequent flts indicated that is the way the FMS works. Reporter felt that any navigation deviation should have been taken care of with a properly working FMS. He felt the FMS system was not working properly, thus, a navigation deviation happened.

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Original NASA ASRS Text

Title: A CRJ65 DEVIATES FOR WX AND INCURS A NAV DEV IN ZDC AIRSPACE.

Narrative: THE FLT DEPARTED THE GATE WITH ALL NORMAL PREFLT OPS COMPLETED. A GND STOP AT PHL REQUIRED US TO SHUT DOWN OUR ENGS AND WAIT 2 HRS ON THE TXWY. THE FMS WAS CHKED SEVERAL TIMES AND CONCURRED WITH THE FLT PLAN AND CLRNC. ON DEPARTING WE WERE REQUIRED TO DEVIATE SEVERAL TIMES DUE TO SEVERE WX. ATC QUESTIONED US SAYING 'WHERE ARE YOU?' AND STATED THAT WE WERE NOT CLRED DIRECT TO FKN. SO WE CHKED THE FMS ONLY TO FIND THE CCV (CAPE CHARLES) HAD DROPPED OUT AND ONLY FKN WAS REMAINING AS THE NEXT POINT. CCV WAS REPROGRAMMED AND WE WERE ABEAM THE FIX (15 MI TO THE W). ACCORDING TO THE MECHS, WHEN DEVIATING IF YOU GET CLOSE TO OR ABEAM A FIX IT WILL DROP OUT. EVIDENTLY THAT IS WHAT HAPPENED. NEITHER OF US REMEMBER IT DROPPING OUT. WE CONTINUED ON WITH THE REST OF OUR FLT PLAN AND NOTHING ELSE WAS EVER SAID BY ATC. THE FOLLOWING DAY THE FMS WAS PROGRAMMED AND FOUND TO BE GIVING ERRONEOUS ROUTES OF FLT. THE MECHS REPROGRAMMED THE DATA ONCE WE RETURNED TO RDU. WE FLEW THREE MORE FLTS AND IT SEEMED TO BE FUNCTIONING PROPERLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR TALKS ABOUT HOW THE WAYPOINT DROPPED OUT OF THE FLT PLAN RTE AND THE NEXT WAYPOINT IN THE FLT PLAN BECAME THE ACTIVE WAYPOINT. RPTR WAS NOT CERTAIN IF THE FMS WAS SUPPOSED TO WORK THIS WAY, HOWEVER, SOME MECHS ON THE SUBSEQUENT FLTS INDICATED THAT IS THE WAY THE FMS WORKS. RPTR FELT THAT ANY NAV DEV SHOULD HAVE BEEN TAKEN CARE OF WITH A PROPERLY WORKING FMS. HE FELT THE FMS SYS WAS NOT WORKING PROPERLY, THUS, A NAV DEV HAPPENED.

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.