How long will masks be required on planes? Flight attendants say mandate should be extendedIt shouldn't be anytime soon, flight attendants say. The union, which represents flight attendants at airlines including United, Alaska, Spirit and Frontier, recently began doling out stickers to vaccinated flight attendants. U.S. airlines have required passengers to wear masks for nearly a year and repeatedly asked for a federal mask mandate to help them enforce it on flights. He said the federal mask mandate will likely be extended but can't be extended forever. He asked Dr. Leonard Marcus, director of the Aviation Public Health Initiative at the Harvard T.H.