Air carrier pilot crew reported the failure of both FMS flight computers during cruise. Crew continued to destination airport and landed.
Synopsis
Air carrier pilot crew reported the failure of both FMS flight computers during cruise. Crew continued to destination airport and landed.
Narrative
During the flight from ZZZ1 to ZZZ we had a dual FMS failure en-route approximately 75 miles from the ZZZ airport. All of the flight phases up until this FMS failure were normal and conducted without incident. We had just exited an approximate 25 min hold at ZZZZZ due to weather in the area and I was inputting a new route into the CA side FMS. This route was given to us by ATC for weather avoidance and traffic flow into ZZZ. I communicated the new route via ACARS to dispatch and we were on our way to the first fix on the new route. Shortly after passing this first fix ATC queried about us being slightly off route. I re-inputted the airway and clicked to execute the change ; at this point FMS1 displayed FMS NOT AVAILABLE. None of the functions of the FMS were usable at this time ; a yellow MAP flag appeared on my MFD (Multi-function Flight Display) and all waypoints / airports / vors disappeared. At this point; I attempted to load FMS2 (FO Side) with the route ; shortly after executing the new route this FMS also failed and displayed FMS NOT AVAILABLE; it also flagged the FOs MFD with a yellow MAP message in the center of the MFD. At this point we decided it was a good idea to [request priority handling] into ZZZ. We were still able to use ACARS and I informed dispatch of the situation. I communicated to the flight attendants the situation; but a normal landing was expected at ZZZ. We requested vectors to ZZZ and were able to accept the ILS to runway XX due to the fact that we could still identify all of the fixes on the approach with the DME from the localizer. All respective phases of flight from the approach; landing; and taxi to the gate were accomplished without further incident. Maintenance met us at the gate and started diagnosing the problem. Cause: The event occurred because we had both FMS1 and FMS2 fail; requiring us to request vectors to ZZZ. We [requested priority handling] because we had lost all waypoints/airports/vors; performance data; automatic fuel burn calculations; ect. and we had already burned through the hold fuel and extra fuel prior to this occurring. We had enough fuel to attempt one approach into ZZZ then have to divert to our alternate airport. Which would have had to be either with radar vectors or VOR to VOR adding to the workload immensely. Suggestions: I'm not sure how you would prevent unanticipated failures from occurring; however some lessons that aimed at making crews aware that even without both of the FMS's; the aircraft can fly VOR to VOR in green needles or you can request radar vectors to the destination if such an event occurred. Also highlighting the approaches that can still be flown without either of the FMSs would be useful information to go over and bring to light that the MFD isn't actually needed to fly an ILS approach or VOR at-all.
Second reporter narrative
After approximately 25 minute hold at ZZZZZ on the ZZZZZ1 arrival; we were given new routing to ZZZ for thunderstorm diversion which put us east of ZZZ as thunderstorms built west and moving rapidly towards the east. Calculating our fuel requirements with the new routing and considering options within busy airspace/ZZZ Center - both FMS failed in flight. First FMS1; then FMS2 a minute or so later. At that point we felt we needed priority handling with a lack of navigational information; performance data; and fuel burn calculations; along dwindling fuel and options. We [requested priority hanlding] with ATC and Captain informed the flight attendants. We continued with vectors for an ILS approach in VMC conditions into RWY XX into ZZZ and landed/taxied to the gate without incident. Cause: The event occurred due to both FMS1 and FMS2 failures; requiring us to request vectors to ZZZ. We [requested priority handling] because we had lost all of our GPS waypoints; performance data; and automatic fuel burn calculations. We had burned through the hold fuel and extra fuel prior to this occurring. With the challenging airspace and thunderstorms surrounding the area; this would have been workload heavy. Suggestions: Training in only 'green needles' / what should pilots do in this situation in the future.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.