Yes, being a competent swimmer is a mandatory requirement for flight attendants (cabin crew) at almost all international airlines. While you don't need to be an Olympic athlete, you must be able to demonstrate "water confidence." Specific requirements vary by carrier; for example, British Airways requires crew to swim 50 meters and tread water for three minutes, while many others require a 25-meter swim unaided. This skill is critical for "ditching" procedures—an emergency water landing. During safety training, recruits must undergo "wet drills" where they enter a pool in full uniform, assist "passengers," and learn how to board and manage a life raft from the water. Some airlines, like Virgin Atlantic, may allow you to apply if you are currently a non-swimmer, provided you take lessons and pass the test before the final training begins. Ultimately, the ability to swim is a non-negotiable safety certification required by aviation authorities to ensure the crew can lead a successful evacuation in the rare event of a water emergency.