Having downloaded the MS SDKs, I see they are listed in Control PanelAdd or Remove Programs. I've also got a downloaded aircraft there too. Is there any reason why I shouldn't remove these?

I'm not entirely sure exactly what you are asking but downloading any of those items alone shouldn't make them visible in Add or Remove Programs, but installing them after downloading obviously does. I have a similar situation. I don't want to uninstall any of them so I will leave them alone. If and when I want to uninstall them I will do that via Add or Remove Programs. I can always reinstall if I want to later from the original downloaded files which I always keep in a special folder. I hope that answers your question and if you decide you don't need the SDK's then by all means uninstall them the same way as I would.

Thanks. It's the first time I'd seen anything other than applications listed in Ad or Remove Programs - I don't often need to use it.Thinking about it, there's no reason why an installer shouldn't do this and provide uninstall instructions, though it seems a bit over the top for SDK Word files!

Yes, I have quite a number of add on planes and even some panels listed there, and many other FS add ons too which one would expect. All the SDK installations are listed, in fact I find it useful as a reminder so I don't have to remember which ones I installed.