Narrative:

During climb out; departure control cleared us direct to ldn; climb to 17000 ft and to maintain 250 KIAS. The FMS was programmed for direct ldn. The aircraft started a left turn. The crew realized this was the wrong direction and took corrective action. The FMS showed a course to ldn as 070 degrees and approximately 256 NM. The correct course was approximately 270 degrees and 15 NM. While turning back to the right direct ldn; ATC queried us as to our direction of flight. The crew explained that the FMS was 'confused' and we were turning back to the right direct ldn. While the crew was trying to determine what was wrong with the FMS and its position; the aircraft was leveled at 17000 ft. While the crew's attention was drawn to the FMS; the aircraft speed increased to around 320 KIAS. ATC called and instructed us to maintain speed of 250 KIAS. The crew promptly complied. There were no known traffic conflicts; no TCASII RA's; and ATC did not advise that any problems were caused. The problem was caused by the crew being distraction by the 'lost' FMS in a busy terminal area. The crew should have promptly advised ATC that there was a problem with the navigation system and requested assistance from ATC until the situation was rectified.

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Original NASA ASRS Text

Title: FLT CREW OF F2TH DEVIATE FROM CLRED TRACK DUE TO FMC IRREGULARITY. ENSUING CONFUSION RESULTS IN DEV FROM ASSIGNED SPD.

Narrative: DURING CLBOUT; DEP CTL CLRED US DIRECT TO LDN; CLB TO 17000 FT AND TO MAINTAIN 250 KIAS. THE FMS WAS PROGRAMMED FOR DIRECT LDN. THE ACFT STARTED A L TURN. THE CREW REALIZED THIS WAS THE WRONG DIRECTION AND TOOK CORRECTIVE ACTION. THE FMS SHOWED A COURSE TO LDN AS 070 DEGS AND APPROX 256 NM. THE CORRECT COURSE WAS APPROX 270 DEGS AND 15 NM. WHILE TURNING BACK TO THE R DIRECT LDN; ATC QUERIED US AS TO OUR DIRECTION OF FLT. THE CREW EXPLAINED THAT THE FMS WAS 'CONFUSED' AND WE WERE TURNING BACK TO THE R DIRECT LDN. WHILE THE CREW WAS TRYING TO DETERMINE WHAT WAS WRONG WITH THE FMS AND ITS POS; THE ACFT WAS LEVELED AT 17000 FT. WHILE THE CREW'S ATTN WAS DRAWN TO THE FMS; THE ACFT SPD INCREASED TO AROUND 320 KIAS. ATC CALLED AND INSTRUCTED US TO MAINTAIN SPD OF 250 KIAS. THE CREW PROMPTLY COMPLIED. THERE WERE NO KNOWN TFC CONFLICTS; NO TCASII RA'S; AND ATC DID NOT ADVISE THAT ANY PROBS WERE CAUSED. THE PROB WAS CAUSED BY THE CREW BEING DISTR BY THE 'LOST' FMS IN A BUSY TERMINAL AREA. THE CREW SHOULD HAVE PROMPTLY ADVISED ATC THAT THERE WAS A PROB WITH THE NAV SYS AND REQUESTED ASSISTANCE FROM ATC UNTIL THE SIT WAS RECTIFIED.

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.