FMS 1 & 2

[stuart11n]

Of all the mysteries and wonders of this beautiful bird this is the one that is bothering me today

What is the difference between FMS 1 and FMS 2?

I see FMS 1 and 2 as options as the navigation source. When I load a flight plan, it loads into FMS 2. AP follows FMS 2, life is good I can get to where I want but how to use FMS 1?

Are they perhaps redundant systems? So if 2 fails, it fails over to 1?

I can't find an explanation in the manual. Can someone help me out?!

Thanks!

[ComputerJones]

They are 2 separate computers for redundancy. When I load a flight plan, both FMS2 and FMS1 have the waypoints. You will notice that, when sitting in the left seat, and selecting "FMS2" as your nav source, the nav data will appear in yellow on the navigation display to let you know that you are using a "cross side" source (conversely, in the right seat, selecting "FMS1" will show in yellow).

They are 2 separate computers for redundancy. When I load a flight plan, both FMS2 and FMS1 have the waypoints. You will notice that, when sitting in the left seat, and selecting "FMS2" as your nav source, the nav data will appear in yellow on the navigation display to let you know that you are using a "cross side" source (conversely, in the right seat, selecting "FMS1" will show in yellow).

Here is an example for you. Here, I have entered a simple flight plan using the FLT PLAN screen on the left CDU, origin KTIW (Tacoma Narrows) and destination KPAE (Paine Field).

Here I have selected FMS1 as my nav source on the left side CDU, and FMS1 as the nav source on the right side CDU.

Note that the left side Navigation Display shows Course, Waypoint, Selected System (FMS1), Distance to go, sequencing mode, and course deviation indicator in white, and this data appears in yellow on the right side ND.

Here I have selected FMS2 as my nav source on the left side CDU, and FMS2 as the nav source on the right side CDU.

Now, on the left side, the navigation data is yellow, and on the right, it is in white. That is because the left side is in "cross source" mode, and the system is telling me I'm doing so.

Bonus: Radio Navigation sources show in green when "same side" selected (e.g., VOR1 in the left seat, VOR2 in the right seat):

And here I have selected VOR2 in the left seat, and VOR2 in the right seat:

I don't think there is an auto failover here, you would have to select the "working" system manually in the NAV SOURCE page should one of the computers bite the dust.