Summary: GAO reviewed the Federal Aviation Administration's (FAA) effectiveness in modernizing the air traffic control (ATC) system and rebuilding its aviation safety work force. GAO found that: (1) actions such as making FAA independent from the Department of Transportation (DOT) or exempting it from procurement regulations would not alone solve ATC modernization and work-force problems; (2) FAA has underestimated the complexity of ATC modernization, resulting in delays in systems development and equipment deployment; (3) FAA may need to request almost $4.5 billion for facilities and equipment in fiscal year 1991 to meet current modernization schedules; (4) FAA has initiated several long-term efforts to improve recruitment, hiring, and training, but will likely not meet its full-performance-level controller staffing goals in the time frames established; (5) maintenance staff shortages may force FAA to contract for maintenance services, rather than perform them in-house; and (6) removing FAA from DOT could damage national transportation planning efforts.