Narrative:

In cruise flight we lost all waypoint and route data on both CDU's with no route displayed on either navigation display. We had no EICAS or status message. The scratchpad on both CDU's had a white 'standby one' message. I tried to input waypoints on both the legs page and the route page. I tried to enter a new route in route 2 page but was unable due to the standby one message. We both tried switching to alternate FMC but the standby one message remained on both CDU's. Due to the fact that we had lost all route and waypoint data and were about to head out over open water and night was approaching; I asked ATC for a heading toward mhlm which was the closest airport displayed on the navigation display. We started a descent to FL300 to remain in VFR conditions. I tried to contact flight control with the satcom but it was inoperative. The first officer (first officer) and I discussed how it was raining heavily in ZZZZ before we departed and we could have water intrusion into the electronics and equipment compartment. I decided to [request priority handling] and ask for vectors to ILS runway 22 in mhlm was the safest course of action. I checked the QRH and only found the FMC message checklist that was not applicable to the situation. After about 15 minutes the white 'standby one' message disappeared and I was able to enter mhlm in the route page and lms in the legs page. We navigated to lms in LNAV. The [company] mechanic in mhlm found extreme corrosion which appears to be carbon buildup on the power connectors on both FMC units in the electronics and equipment compartment. Attached are photos of the power plugs the mechanic took. Carbon buildup can cause an electrical fire and this is a serious concern that needs to be addressed.

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Original NASA ASRS Text

Title: B757-200 flight crew reported Flight Management Computer failure inflight.

Narrative: In cruise flight we lost all waypoint and route data on both CDU's with no route displayed on either navigation display. We had no EICAS or Status message. The scratchpad on both CDU's had a white 'Standby One' message. I tried to input waypoints on both the legs page and the route page. I tried to enter a new route in Route 2 page but was unable due to the standby one message. We both tried switching to alternate FMC but the Standby One message remained on both CDU's. Due to the fact that we had lost all route and waypoint data and were about to head out over open water and night was approaching; I asked ATC for a heading toward MHLM which was the closest airport displayed on the navigation display. We started a descent to FL300 to remain in VFR conditions. I tried to contact flight control with the SATCOM but it was inoperative. The FO (First Officer) and I discussed how it was raining heavily in ZZZZ before we departed and we could have water intrusion into the Electronics and Equipment compartment. I decided to [Request Priority Handling] and ask for vectors to ILS Runway 22 in MHLM was the safest course of action. I checked the QRH and only found the FMC MESSAGE checklist that was not applicable to the situation. After about 15 minutes the white 'Standby One' message disappeared and I was able to enter MHLM in the route page and LMS in the legs page. We navigated to LMS in LNAV. The [Company] Mechanic in MHLM found extreme corrosion which appears to be carbon buildup on the power connectors on both FMC units in the Electronics and Equipment compartment. Attached are photos of the power plugs the mechanic took. Carbon buildup can cause an electrical fire and this is a serious concern that needs to be addressed.

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.