Narrative:

Shortly after passing over hpw fix; the FMS started on the argal 5 arrival; then proceeded directly to rdu. After ATC queried; we took a heading; got back on course; no issues or conflicts stated by ATC. The FMS dropped the arrival on the mfd; but kept it in the box. After going directly to fix; the FMS drew a strange course past the missed approach; and onto a random fix over 100 NM away. We both looked bewildered along with another captain in the jumpseat. After deleting the random fix into the future; the PF (captain) then drew a normal course on the mfd. At this time; I could not believe my eyes as; he cleared out his FMS with the random fix; my mfd drew the same course out of nowhere. I now had a strange course on my mfd; I quickly deleted the strange fix; and we decided that the FMS would not be useful any more. After telling ATC that we had malfunctioning avionics; we took a heading proceed to an extended final and contacted maintenance on the ground. We suspected that due to having 5 electrical sensitive MEL's on the plane; then reduced to 4 we thought that maybe they could be connected. With over 15-20 combined yrs between the 3 pilots in the cockpit; all of us had never seen anything like that before. I hope this issue gets resolved before another flight crew accepts it. Random FMS behavior; quick communications between crew allowed for immediate course realignment; and using 'green world' technology.

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Original NASA ASRS Text

Title: EMB135 FO REPORTS STRANGE FMC MALFUNCTION DURING ARGAL ARRIVAL TO RDU CAUSING TRACK DEV.

Narrative: SHORTLY AFTER PASSING OVER HPW FIX; THE FMS STARTED ON THE ARGAL 5 ARR; THEN PROCEEDED DIRECTLY TO RDU. AFTER ATC QUERIED; WE TOOK A HDG; GOT BACK ON COURSE; NO ISSUES OR CONFLICTS STATED BY ATC. THE FMS DROPPED THE ARR ON THE MFD; BUT KEPT IT IN THE BOX. AFTER GOING DIRECTLY TO FIX; THE FMS DREW A STRANGE COURSE PAST THE MISSED APCH; AND ONTO A RANDOM FIX OVER 100 NM AWAY. WE BOTH LOOKED BEWILDERED ALONG WITH ANOTHER CAPT IN THE JUMPSEAT. AFTER DELETING THE RANDOM FIX INTO THE FUTURE; THE PF (CAPT) THEN DREW A NORMAL COURSE ON THE MFD. AT THIS TIME; I COULD NOT BELIEVE MY EYES AS; HE CLRED OUT HIS FMS WITH THE RANDOM FIX; MY MFD DREW THE SAME COURSE OUT OF NOWHERE. I NOW HAD A STRANGE COURSE ON MY MFD; I QUICKLY DELETED THE STRANGE FIX; AND WE DECIDED THAT THE FMS WOULD NOT BE USEFUL ANY MORE. AFTER TELLING ATC THAT WE HAD MALFUNCTIONING AVIONICS; WE TOOK A HDG PROCEED TO AN EXTENDED FINAL AND CONTACTED MAINT ON THE GND. WE SUSPECTED THAT DUE TO HAVING 5 ELECTRICAL SENSITIVE MEL'S ON THE PLANE; THEN REDUCED TO 4 WE THOUGHT THAT MAYBE THEY COULD BE CONNECTED. WITH OVER 15-20 COMBINED YRS BTWN THE 3 PLTS IN THE COCKPIT; ALL OF US HAD NEVER SEEN ANYTHING LIKE THAT BEFORE. I HOPE THIS ISSUE GETS RESOLVED BEFORE ANOTHER FLT CREW ACCEPTS IT. RANDOM FMS BEHAVIOR; QUICK COMS BTWN CREW ALLOWED FOR IMMEDIATE COURSE REALIGNMENT; AND USING 'GREEN WORLD' TECHNOLOGY.

Data retrieved from NASA's ASRS site as of May 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.