I fly for a Fortune 20 flight department. I also do some outside flying if I am contacted. I get to get keep 100% of what I make. But when I get called I make sure I ask my boss if I can do it, even if I am not on the schedule that day. There have been times he has even changed the schedule and taken me off a trip so that I can go make money somewhere else. The guys I fly with are all good guys and don't have a problem with that. We all cover for each other.
We have a couple of guys who get alot of time off to fly in the AF Reserves. Since he has to give guys time off to do that and they get paid to do it he thinks it's only fair that if I get a chance to make money on the side.