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.