Narrative:

FMC selector switch in left and position reference 2 page left as primary. On track at FL360 we had a dual FMC failure; shortly after making a route modification to the arrival airport. We got the following malfunctions: amber autopilot caution followed by VNAV with a line through it. No magenta course line on either map with route 1; route 2; and the legs page operating normally. LNAV was engaged and in green. We tried to repair the loss of the route on our map by going to RTE2 to activate that. In the interim we went flch opened the speed window to M84. While trying to clean up route 2 we got 'standby one' in the FMC scratch pad with the following indications: LNAV with a line through it; map inop on both maps; loss of all data in route 1. We went to heading select to keep on course. Standby one lasted about 1 min; during that time we could not operate either FMC. After it went away our maps came back as well as the fmcs. We put our next point on the fix page while waiting and when the fmcs came back put that point in route 1. Then rebuilt the rest of the route. LNAV was available again so we reengaged it. We fixed VNAV by putting in a cruise altitude and reloading the perf page; then reengaging it. About 30 minutes after the event we got radar contact with ATC and reported that we had a loss of navigation for a short period of time. They confirmed we were on course. As far as I know we were on course the entire time even when in heading select.

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Original NASA ASRS Text

Title: While at cruise on an oceanic route; B777 flight crew modified the destination airport's arrival in the FMC RTE 1 page. A dual FMC failure occurred shortly after; but the crew rebuilt the route and returned both FMCs to normal operation.

Narrative: FMC selector Switch in L and POS REF 2 page L as primary. On track at FL360 we had a Dual FMC failure; shortly after making a RTE modification to the Arrival airport. We got the following malfunctions: Amber Autopilot Caution followed by VNAV with a line through it. No magenta course line on either MAP with RTE 1; RTE 2; and the legs page operating normally. LNAV was engaged and in green. We tried to repair the loss of the route on our MAP by going to RTE2 to activate that. In the interim we went FLCH opened the speed window to M84. While trying to clean up RTE 2 we got 'Standby One' in the FMC scratch pad with the following indications: LNAV with a line through it; MAP inop on both MAPs; loss of all data in RTE 1. We went to HDG select to keep on course. Standby One lasted about 1 min; during that time we could not operate either FMC. After it went away our MAPs came back as well as the FMCs. We put our next point on the Fix page while waiting and when the FMCs came back put that point in RTE 1. Then rebuilt the rest of the RTE. LNAV was available again so we reengaged it. We fixed VNAV by putting in a Cruise Altitude and reloading the PERF page; then reengaging it. About 30 minutes after the event we got radar contact with ATC and reported that we had a loss of NAV for a short period of time. They confirmed we were on course. As far as I know we were on course the entire time even when in Heading select.

Data retrieved from NASA's ASRS site 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.