I've never worked for an airline, but I know that one of the benefits of working in the industry is that you can fly for free or almost free on a space-available basis. I realize that every airline is slightly different, but what's the general procedure for this? To provide a concrete example, let's say I live in New York and want to non-rev to Miami tomorrow.

How would I know if a space is available? How far ahead will I know that I have a seat? Can more senior employees beat me out or is it first come, first served? Do I need a boarding pass? If not, how do I get past the TSA checkpoint?

In general, how does flying non-rev work?