The Federal Aviation Administration's (FAA's) microwave landing system (MLS), which is designed to replace existing instrument and other landing systems, is to be an all-weather precision guidance system making instrument landings possible at more locations and providing flexibility in approach paths. It is expected to be easier to install and maintain and less expensive than the current system. A high level of uncertainty exists in the Department of Transporation and the aviation community concerning the overall expected benefits of the MLS. It is generally believed that instrument landing systems are reliable, safe, and provide efficient service within technical and operational capabilities. However, the current system is limited to 40 channel frequencies; it does not meet military tactical requirements; and it is adversely affected by heavy snow, irregularities in the terrain, and structures built close to the runway. The MLS is expected to overcome these limitations. The total research and development effort for the MLS program will be between $90 million to $100 million more than originally estimated. No urgent need exists for the military MLS systems; therefore, to plan for production deliveries of both civil and military systems in 1985 and an initial operating capability in 1986 appears unnecessary.