Summary: GAO discussed fundamental weaknesses in the Federal Aviation Administration's (FAA) acquisition of major automated systems. GAO noted that, under the Mode Select procurement, FAA: (1) decided to purchase an additional 259 air traffic control systems before it tested any of the 137 systems it originally ordered; (2) spent about $145 million before receiving the first system; (3) did not remedy technical problems as they arose, causing significant delivery delays; (4) did not adequately develop or test the system before awarding the production contract; and (5) did not properly analyze requirements, adequately consider alternatives, or evaluate benefits and costs. GAO also noted that FAA experienced problems in acquiring its Advanced Automation System, due to: (1) an overly ambitious software development schedule; and (2) the contractor's inability to resolve key requirements problems. In addition, GAO noted that FAA inadequately justified its Computer Resources Nucleus (CORN) procurement, since it: (1) could not support its claims regarding insufficient computer capacity, poor response times, and increased data processing needs; (2) lacked a reliable method for validating bidders' proposed solutions; (3) did not provide bidders with complete information about the requirements; and (4) based its cost estimate for converting to CORN on unsupported assumptions regarding staff resources and unit costs.