In response to a congressional request, GAO evaluated the Federal Aviation Administration's (FAA) requirements for participation in its Airport Certification Program, particularly: (1) its requirements for commuter airlines with 30 or fewer passenger seats; (2) the program's safety benefits and cost-effectiveness; and (3) alternative requirements and their impact on commuter airports. GAO found that: (1) airports that serve only commuter airlines with less than 31 passengers cannot acquire certification; (2) many currently certified airports could lose their certification because they no longer meet FAA participation requirements; (3) the program has increased airport safety by reducing the risk of accidents and enhancing airports' ability to deal with accidents; (4) airport certification costs ranged from $25,000 to $313,000 for capital costs, $8,200 to $77,000 for annual operating costs, and $820 to $2,100 for FAA inspection and recertification; (5) a grant program under the Airport and Airway Improvement Act of 1982 could cover most of airports' capital costs; and (6) implementation of alternative participation requirements would increase the number of certified commuter airports.