FSX .AIR files

Which program do i use to view .AIR files, i am using FS Tweaks and it is asking for a directory to my .AIR viewing Program.

Use notepad.

Notepad is used to open the aircraft.cfg file NOT the .air file. You'll need something like AirEd:

http://pagesperso-orange.fr/hsors/fsairfile.html

I can't verify that this app works with the FSX .air files, just give it a try. Make sure you keep a copy of the original before you start tweaking.