Which agency of the U.S. government has the primary responsibility for regulating aviation safety?

The Federal Aviation Administration (FAA) is the correct choice because it is the primary agency responsible for ensuring the safety of civil aviation in the United States. The FAA's mission includes regulating all aspects of civil aviation, including the certification of pilots and aircraft, establishing air traffic control standards, and enforcing safety regulations that govern aircraft operations. The agency is also tasked with overseeing the design and maintenance of aviation infrastructure, further enhancing the safety of air travel.

In contrast, the National Aeronautics and Space Administration (NASA) focuses primarily on space exploration and aeronautics research, rather than the direct regulation of aviation safety. The Federal Bureau of Investigation (FBI) has a broader law enforcement role related to national security and criminal investigations, which does not specifically include aviation safety. The Transportation Security Administration (TSA) is concerned with the security of the transportation system, particularly concerning airport security and passenger screening, rather than the wider scope of aviation safety regulation handled by the FAA.