Narrative:

Just after takeoff we had a dual FMC failure. Captain was pilot flying and took control of aircraft while both first officers ran checklists and com. Captain asked nfp (non-flying pilot) to quickly tell ATC we have lost all navigation capability and get a vector. Busy frequency and when able to broadcast he was unable to transmit. Observer first officer (first officer) took communications and told ATC. By this time ATC could see we were off course and asked if we had terrain ahead in sight and we replied yes and could maintain clearance. Ca (captain) started a turn to [the] right. ATC had us turn back to heading 140 for a moment and then 090 climb to 9;000 feet. At this time we got basic nav back per checklist and continued on course. Contacted dispatch; [maintenance]; [chief pilot] via satcom. Elected to continue at least to [an alternate airport] if not all the way to [our destination]; had lots of fuel to burn or dump regardless. We had concerns about class 2 nav without FMC limitations in vol 1. About 1hr into flight recovered left FMC only and continued to [our destination]. Heavy rain [at origin airport] and we suspect that water got into east/east [electrical/electronic] compartment?be more proactive during heavy rain to ensure ground crews and flight crew keep L1 door shut. Now that myself and [the] crew have experienced a dual FMC failure at one of the worst times of a flight; I will certainly be better prepared in the future. Thankful for a good experienced crew and CRM. We talked it through once established on a safe heading and altitude and got the company personnel involved via satcom.

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Original NASA ASRS Text

Title: B747 flight crew reported that during climb the aircraft lost all navigation systems and had a dual FMC failure.

Narrative: Just after takeoff we had a dual FMC failure. Captain was pilot flying and took control of aircraft while both First Officers ran checklists and com. Captain asked NFP (non-flying pilot) to quickly tell ATC we have lost all navigation capability and get a vector. Busy frequency and when able to broadcast he was unable to transmit. Observer FO (First Officer) took communications and told ATC. By this time ATC could see we were off course and asked if we had terrain ahead in sight and we replied yes and could maintain clearance. CA (Captain) started a turn to [the] right. ATC had us turn back to heading 140 for a moment and then 090 climb to 9;000 feet. At this time we got basic Nav back per checklist and continued on course. Contacted Dispatch; [Maintenance]; [Chief Pilot] via SATCOM. Elected to continue at least to [an alternate airport] if not all the way to [our destination]; had lots of fuel to burn or dump regardless. We had concerns about class 2 Nav without FMC limitations in Vol 1. About 1hr into flight recovered L FMC only and continued to [our destination]. Heavy rain [at origin airport] and we suspect that water got into E/E [Electrical/Electronic] compartment?Be more proactive during heavy rain to ensure ground crews and flight crew keep L1 door shut. Now that myself and [the] crew have experienced a dual FMC failure at one of the worst times of a flight; I will certainly be better prepared in the future. Thankful for a good experienced crew and CRM. We talked it through once established on a safe heading and altitude and got the company personnel involved via SATCOM.

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.