" The Federal Aviation Administration (FAA), partnering with other federal agencies and the aviation industry, is implementing the Next Generation Air Transportation System (NextGen), a new satellite-based air traffic management system that will replace the current radar-based system and is expected to enhance the safety and capacity of the air transport system by 2025. Concurrently, FAA continues to maintain and upgrade existing air traffic control (ATC) systems that will also be needed for NextGen. This involves acquiring and implementing new software and hardware. GAO was asked to determine (1) how, if at all, costs and schedules of FAA ATC acquisitions programs, including those related to NextGen, have changed since they were first submitted to Congress, (2) the reasons for any such changes, and (3) the extent that selected ATC programs adhere to cost and schedule best practices. To do its work, GAO reviewed 30 programs and conducted cost and schedule analysis on four programs that had an approved baseline and were NextGen related. GAO reviewed acquisition documents and interviewed FAA officials. "