Yes, it would be different flying internationally. Whenever he returns through border control, if he has a warrant, they will arrest him. His best advice is to resolve the warrant before he leaves the country or else he faces arrest upon return.
Just for clarity sake it's not the airline that does the security check. The airline gives the passenger manifest to Homeland Security who does the rest. My research tells me they focus on people who might have terrorist connections and do not search outstanding warrants.
I agree with the analysis of both of my colleagues, and also agree with the suggestion that he needs to resolve the warrant as soon as possible. Good luck.
DISCLAIMER I do not practice law in your State. This answer is provided solely for informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.