Just curious about the ability to use/purchase daily lounge access for one airline when flying on another.

Let's say I have an AA ticket - can I go buy a day pass for another airline? Or do they require you to be flying that airline?

What about if you have lounge access due to status - If I am an AA elite member, or a United CC holder (which gives lounge access) - do I need to be flying on THAT airline that day?

thanks!