Why do you think that Frank pays the expenses for his crew of interns personally rather than coming up with a scheme for getting Pan Am to pay them?

He probably wants to make sure that he is not going to get caught before he even gets to Europe. Also, it is easy for a pilot to deadhead across the country and around the world. But it is not standard practice for an entire flight crew to deadhead -- to try to do such a thing attracts suspicion.