You can't. You can, however, open multiple windows, and those windows can operate independently.
Thank you, Joe.
when I try to start 2 instances of AIR app that has background music playing in background (double-clicking twice on desktop shortcut icon), I hear the music being played "with echo" (like you started 2 instances of players of same mp3; one after another with slight delay in between).
This is the symptom that somehow actually "2 instances are running in 1 application window". Another symptom is that everything becomes noticeably slower. This is 100% reproducible on all windows platforms tested (7, XP, Vista). Restarting it (with just 1 double-click), all is normal.
It is my understanding that this is or should be taken care of by AIR platform (in fact, single running instance is enforced) and could not be an error in our code. Please confirm.