Narrative:

In cruise we were given direct ink. When line selected to the legs page it showed as the letter 'D' with no other latitude/longitude; etc; information. Upon second try; line selected ink but sso showed in scratch pad. Third try worked normally. Kept the airplane a second leg with no further anomalies. Usually I might not report this but yesterday we had a dropped fix and we were watching particularly close today with deliberate FMC entries. Having flown FMC's for over 10 yrs now; I have found the B737 to be particularly reliable. Now with 2 days and 2 strange occurrences; I will be watching the FMC really close. Just curious if other reports have increased. Could the software be less stable? Could it be onboard electronic interference?

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Original NASA ASRS Text

Title: B737-800 CAPT RPTS ANOMALOUS FMC RESPONSES.

Narrative: IN CRUISE WE WERE GIVEN DIRECT INK. WHEN LINE SELECTED TO THE LEGS PAGE IT SHOWED AS THE LETTER 'D' WITH NO OTHER LATITUDE/LONGITUDE; ETC; INFO. UPON SECOND TRY; LINE SELECTED INK BUT SSO SHOWED IN SCRATCH PAD. THIRD TRY WORKED NORMALLY. KEPT THE AIRPLANE A SECOND LEG WITH NO FURTHER ANOMALIES. USUALLY I MIGHT NOT RPT THIS BUT YESTERDAY WE HAD A DROPPED FIX AND WE WERE WATCHING PARTICULARLY CLOSE TODAY WITH DELIBERATE FMC ENTRIES. HAVING FLOWN FMC'S FOR OVER 10 YRS NOW; I HAVE FOUND THE B737 TO BE PARTICULARLY RELIABLE. NOW WITH 2 DAYS AND 2 STRANGE OCCURRENCES; I WILL BE WATCHING THE FMC REALLY CLOSE. JUST CURIOUS IF OTHER RPTS HAVE INCREASED. COULD THE SOFTWARE BE LESS STABLE? COULD IT BE ONBOARD ELECTRONIC INTERFERENCE?

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.