Airplane regulation is handled worldwide by individual countries. For example, the United States has the Federal Aviation Administration, under the United States Department of Transportation, which oversees all air travel and aviation in America. The Federal Aviation Administration is first and foremost concerned with safety regulations. This includes passenger and airline safety and regulation covering safety issues is extensive. For example, FAA regulations part 23 is one of the agency's most well known regulations and covers the airworthiness of an airplane. To pass inspection a plane must pass all regulation sections listed in part 23. These include regulations on the number and placement of seats in a plane, emergency landing procedures, and fire prevention systems. Airplane regulation came to public attention after September 11, 2001. When terrorists attacked the Twin Towers in New York City travellers worldwide suddenly had second thoughts about air travel. And, for the first time in airline history, all United States flights and flights into and out of the country were grounded for an extended time. Since this time regulation of airplanes has become extensive to ensure passenger safety.