Among its responsibilities for aviation safety, the Federal Aviation Administration (FAA) issues thousands of certificates and approvals annually. These certificates and approvals, which FAA bases on its interpretation of federal standards, indicate that such things as new aircraft, the design and production of aircraft parts and equipment, and new air operators are safe for use in the national airspace system. Past studies and industry spokespersons assert that FAA's interpretations produce variation in its decisions and inefficiencies that adversely affect the industry. GAO was asked to examine the (1) extent of variation in FAA's interpretation of standards for certification and approval decisions and (2) views of key stakeholders and experts on how well these processes work. To perform the study, GAO reviewed industry studies and reports and FAA documents and processes; convened a panel of aviation experts; and interviewed officials from various industry sectors, senior FAA officials, and unions representing FAA staff. GAO recommends that FAA develop a continuous evaluative process with measurable performance goals to determine the effectiveness of the agency's actions to improve its certification and approval processes. The Department of Transportation provided technical comments, which were included as appropriate.