'Secret Airline Codes' That Save Travelers Cash | Know what air travelers get with AA, DL and UA ? . Fly those airlines (American, Delta, United) with a single checked bag and you get a $50 fee . But there are two acronyms that can help save money . Especially when shopping for plane tickets . You may never stumble across these three letter codes, not unless you study raw airfare data like I do, but you don't need to see them to use them to your advantage.