The way iOS works is that every app lives in its own 'sandbox'. For security reasons, apps cannot access the sandboxes of other apps. They can only communicate with each other using certain defined channels, such as "Send To".
If you have data in an app such as Air Nav Pro, the only "official" way to get that data out is if the app supports sending it to another app. In which case you can send it to Dropbox, GoodReader or something else and send it to your PC from there. For obvious reasons (copyright, licensing), Air Nav Pro does not support that.
The unofficial way is to "jailbreak" your iPad. That will eventually allow you to install applications that can look in all sandboxes. It also may void, or limit, support/warranty from Apple. And if Air Nav Pro somehow stores its data in an encrypted or proprietary format, it may not help anyway.
The third way which I'm not entirely sure about, but which might work, is that iOS 5 apps are able to upload some or all of their data to the iCloud - essentially a huge Apple database on the internet. I don't know if Air Nav Pro does that for its maps data (my gut feeling tells me it doesn't, but I haven't checked) but if it does, you might be able to get the data from the iCloud via, for instance, iTunes or the iCloud website. I don't use iCloud myself though, so I can't help you further with that.
But seeing as Air Nav Pro makes a lot of money from selling maps, I am fairly certain that they've made it very hard for users to be able to use those maps outside of Air Nav Pro.