Miroku: "Suggest you also look at Sky Demon flight planning. If you eventually buy it then could you PM me, as I'll then be one third of the way to a free year's subscription."
Sadly Sky Demon doesn't run on an iPad, or on any Apple OS natively.
I run it on Parallels/Windows 7 on a MacBook Pro, and very good it is too. You could run the internet version on an iPad using a browser I suppose, but I wouldn't expect that would work in the air...