Is this at all a plausible sitation? If he'd worked that long in the US, I'm guessing he'd have to have had a green card. As a pilot with an international route, he would be very aware of the laws (unlike myself). If he had a passport, would they be able to detain him?
I've searched variations of British citizen working in US, work visa, foreign national employment in US. What information I've found is difficult to understand, being written in legalese. I'd love personal experience or a good interpreter of legal statements.