creat the look of characters changing on airport depature display

[Tim Kurkoski]

What kind of display? Newer airports simply use computer graphics on LCD panels hanging in the terminals, not hard to replicate. Or were you thinking about an LED display? There are fonts out there you can get to do that.

I suspect you’re talking about the old-style flip lettering boards, though. Off the top of my head, I’d say you’re in for using a lot of layers, and animating them in 3D to flip. One trick that may help is to set the letters for a particular space on the board in a pre-comp and to use time remapping to control which one appears. See this tutorial to get an idea of how time remapping can be used in this fashion:
https://www.creativecow.net/articles/rabinowitz_aharon/lip_synch/index.html

You’ll probably want to actually animate the flipping cards in the pre-comp, though, and enable motion blur for the layers.