FL240 refers to a flight level of 24,000 feet above sea level. In aviation, flight levels are used to indicate altitude in a standardized way, measured in hundreds of feet. FL240 is commonly used by commercial aircraft during cruising phases of flight, where they operate efficiently and safely above most weather disturbances. At FL240, aircraft are typically flying in controlled airspace, which is managed by air traffic control. This altitude allows for adequate separation between different aircraft, reducing the risk of mid-air collisions. Pilots and air traffic controllers use this designation to ensure safe navigation and communication during flights.