FL190 refers to a flight level of 19,000 feet above sea level. In aviation, flight levels are used to indicate altitude in a standardized way, measured in feet. FL190 is commonly used by commercial and private aircraft during cruising phases of flight, providing a safe altitude above terrain and weather. At FL190, aircraft typically operate in controlled airspace, where air traffic control manages the flow of air traffic. This altitude helps maintain separation between different aircraft and ensures safety during flight. Pilots must adhere to specific regulations and procedures when flying at this level, including communication with air traffic control.