Pursuant to a congressional request, GAO evaluated the Federal Aviation Administration's (FAA) progress in: (1) rebuilding the air traffic controller and safety work forces; and (2) developing a plan to address aging aircraft problems. GAO found that: (1) FAA had rebuilt the air traffic controller work force since the 1981 strike, but the number of full-performance-level (FPL) controllers was still about 2,400 below pre-strike levels; (2) as of September 1990, only 10,800 controllers were FPL, and most facilities were below the FAA goal that 75 percent of the controller work force be FPL; (3) in June 1989, FAA initiated a 5-year pay demonstration project to encourage experienced controllers to relocate or remain at the busiest air traffic facilities, but the project had limited success after almost 2 years; (4) to decrease the current 45-percent controller training failure rate and its associated costs of over $13 million annually, FAA developed two projects to explore alternatives for screening and hiring controllers; (5) since the aviation inspector work force has grown from 1,500 in 1983 to 2,577 in September 1990 and is not expected to increase much beyond 3,000, FAA must use its current inspectors more effectively and provide them with better training; and (6) FAA has worked closely with the aviation community to improve the safety of the aging commercial transport fleet, but has not yet completed a comprehensive plan to guide industry and government efforts to address aging aircraft concerns.