I dont really see how much time it's going to save you.
You are still going to have to go through each route and edit it for the new aircraft. :wink:
If you put it that way... I would imagine it like this - plane properties menu - replace button - choose new aircraft - then you get a nice page with all routes and their prices, frequencies. You edit everything to suit your needs - press next and voila.
And it also would save more than closing routes. It would save closing route, remembering what route it was (writing it down, or keeping that window open), creating new route and edit it. It's not so bad if you want to replace 1 aircraft. But if you just received 10 aircrafts?
It would also be great if we could select few planes and then click replace. In this case there wouldn't be empty spaces in planes timetables. What I mean is, let's say I have two planes, with two one hour routes (4 hour total) and I have one plane, which can travel same route in, let's say 2 hours. So if i click replace for both of the previous planes, it would put all routes into one plane, rather than a simple transfer... Some sort of append function... Anyway, I'm getting lost myself here, I hope you don't.