A KC-135 tanker typically requires Programmed Depot Maintenance, or PDM, every five years. Boeing inspects the aircraft and performs necessary maintenance and repairs, ensuring readiness for five years or more. Aircraft undergoing PDM are not available to support combat operations. Boeing's role, therefore, is to complete its work and return a quality product back to the Air Force as quickly as possible. Through a series of lean activities, Boeing is shortening the amount of time each aircraft spends in PDM.