So this was written a few bankrupts' ago and whilst I'd still like to see this feature, I'd like to expand upon it slightly.
I'd like to be able to assign a category (color/name/number) to each aircraft and to each route.
The primary reason is that when I have 2 pages of one aircraft type or 9 pages of routes for one of my aircraft types, of I'd like the option to be able to refine that down to a select few using existing functions in the interface.
I think this could be achieved by each detailed route page and each detailed aircraft page having a text box for a user defined name and/or number (call it RouteGroup and AircraftGroup if you like).
In the Route Management Page (Routes|Manage) when pulling down the aircraft type (Fleet Group), there could be an option (above or below a separator) to include names RouteGroup names or it could have it's own pull-down menu for this data called Route Group.
In the Scheduling Page (Routes|Scheduling) when pulling down the aircraft type (Fleet Group), there could be an option (above or below a separator) to include names AircraftGroup names or it could have it's own pull-down menu for this data called Aircraft Group.
I see this as a mechanism that could further improve the interface.