What was found
THE FMC'S SEEM TO DROP WAYPOINTS ON THE RNAV ARRIVALS WHEN THE RUNWAY/APPROACH IS CHOSEN OR CHANGED. NO DISCO APPEARS, THEY JUST RANDOMLY CONNECT TWO POINTS OMITTING SOME BUT NOT ALL OF THE WAYPOINTS. GROUNDED - YES. COULD NOT DUPLICATE DISCREPANCY. #1 AND #2 FMC BITE SHOWED NO RELEVANT FAULTS LAST FLIGHT, REF B737-900 FIM 34-61 TASK 801. VERIFIED NAV DATA BASE IS CURRENT AND VERIFIED THAT BOTH FMC'S ARE LOADED WITH THE CORRECT SOFTWARE, REF B737-900 IPC 34-61-02. NO HISTORY LAST 90 DAYS.