An Airline Transport Pilot License (ATPL) is the highest level of pilot certification and is required to act as the captain of a commercial airline aircraft. It requires significant experience, typically around 1,500 flight hours, along with advanced theoretical exams, instrument rating, and multi-engine qualification. The ATPL holder is responsible for overall command of the aircraft, safety of passengers, and decision-making during all phases of flight. It represents the highest level of skill, training, and responsibility in the aviation industry, qualifying pilots for senior command positions in airlines worldwide.