I don’t think that’s technically true. There is a form your CC can fill out and approve outside employment. But it’s not required. Just as long as your other job is on a non interference basis and doesn’t have a conflict of interest. Meaning you can’t do a job that is directly related to your mil job. Because that would create a bias. Otherwise as long as you don’t have a bias and you are doing it on your free time or leave that has been approved, there shouldn’t be any legal issue. With regards to the airlines, I have no idea. But I’ve known people flying for the majors prior to terminal. And on active duty or guard or reserve.