B757-200 flight crew reported the FMCs failing during the climbout.
Synopsis
B757-200 flight crew reported the FMCs failing during the climbout.
Narrative
During climb-out at approximately FL260; both FMC's went blank; [and the] Captain's PFD (Primary Flight Display) had numerous yellow flags. Raw data attitude; speed; and altitude indications were not affected when compared to the standby attitude and FO's (First Officer) instruments; based on the call-outs he was making. AT (Autothrottles) disconnected; autopilot remained engaged but in a degraded state. Complied with QRH for L FMC FAIL EICAS message. Captain's PFD returned to normal after QRH. L FMC FAIL and FMC MESSAGE EICAS Message remained entire flight. During this issue we also had FMC R OUTPUT LOSS scratchpad message. SINGLE FMC R OPERATION scratchpad message at block-in. After completing the checklists and re-automating the airplane; we confirmed we had good lateral navigation from the FMS; but no vertical navigation returned. After discussing why; I noticed the zero fuel weight did not come back after the R FMC was reselected. After re-entering the zero fuel weight; all of the VNAV capabilities returned and operated normally. We continued to ZZZ1 without any more issues. Not sure what caused this issue. We thought originally [that] we had a lightning strike; but ZZZ1 Maintenance found no evidence of one. There was a lot of static electricity and St. Elmo's Fire on the windscreen prior to the FMC failure.
Second reporter narrative
During climb-out passing approximately FL260 both FMC's went blank and numerous yellow flags appeared on the left and right PFDs (Primary Flight Display). Near simultaneously; the AT (Autothrottles) disconnected but the autopilot remained engaged in a degraded state. The raw data of pitch and airspeed remained intact so the CA (Captain) continued climb utilizing that information. We notified ZZZ Center that we had lost navigation capability and requested to maintain current heading and climb to FL390 while we assessed the situation. We ran the QRH for the following EICAS messages: L FMC FAIL and FMC MESSAGE. The CA's PFD returned to normal once he switched to FMC-R per the checklist. After completing QRH checklists; the L FMC FAIL; FMC MESSAGE remained displayed [for] the remainder of the flight. Additionally; we had an FMC R OUTPUT LOSS scratchpad message and SINGLE FMC R OPERATION scratchpad message at block-in. After running all the checklists; the CA re-automated the airplane and we determined that lateral navigation was intact but were suspect of vertical navigation as VNAV was not providing valid data. After consulting with Dispatch and Maintenance Control; we decided to continue to destination. We did not declare an emergency but discussed our vertical navigation limitations with each ATC controller enroute. We did not have any further issues during enroute; arrival and landing at ZZZ1.I originally suspected a lightning strike as we were climbing through heavy precipitation with a few white flashes just prior to the event. However; upon landing at ZZZ1; Maintenance personnel did not see any obvious lightning strike damage. Therefore; I surmise that there was an electrostatic event that occurred as there was significant St. Elmo's Fire on the windscreen just prior to and during the event.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.