You tip the airport bartender, the hotel shuttle driver, and maybe even the person who delivers food to your gate, so what happens when a flight attendant hands you a drink at 35,000 feet? For many travelers, tipping flight attendants occupies a strange gray area because the interaction can look a lot like other service jobs where gratuities are expected. Yet flight attendants aren’t primarily onboard to serve drinks or snacks, and tipping has never become a standard expectation across U.S. airlines. There have even been disagreements within the airline industry about whether tipping should be encouraged at all. Before pulling out cash after your next complimentary coffee, here’s what travelers should understand about the etiquette and why your flight attendant’s job is very different from your restaurant server’s.