So, due to compile issues you are currently unable to load the Backtrack OS directly to a Raspberry PI (Arm versions differ), it is therefore required that the most popular programs are installed onto the OS manually. As I work through them myself, I will be recording the steps.
Update: Scrap that. You need the Debian version of aircrack-ng and I am buggered if I can find it. Will start the hunt now, but a few locations have failed me.
On the plus side a Raspberry OS called pwnpi is available at the following location, and is intended for penetration testing purposes http://sourceforge.net/projects/pwnpi/
First item on the list, is aircrack-ng-1.1.