NASA this week commemorated the 50th anniversary of the blanket ban on civilian supersonic flight over the United States. The milestone comes as the agency continues to develop the X-59 experimental supersonic aircraft designed to reintroduce civilian Mach+ into service.
April 27, 1973, United States Federal Aviation Administration (FAA) has implemented a new rule that prohibits civilian aircraft from flying over US land or territorial waters at speeds exceeding Mach 1. The decision follows the introduction of the Aircraft Noise Abatement Act of 1968 and growing public concern about the impact of military sonic booms on certain parts of the country.
Sonic booms are unpleasant and potentially destructive things. In short, they are the result of shock waves formed in front of a supersonic aircraft. As the plane flies overhead, the built-up energy is released in the form of a boom loud enough to shatter window glass and startle livestock and wildlife.
Given this, the 1973 ban made sense from an environmental point of view, but the significance of the regulation goes far beyond simple ecological protection. Some support for it comes from groups that oppose supersonic flight for ideological reasons, while others support it as a way to protect the U.S. aerospace industry by shooting at foreign competitors.
By 1973, the United States was effectively out of the race to win the next revolution in air travel, the development of a practical commercial supersonic airliner. The U.S. government supported several projects by Boeing, General Electric, and Lockheed, but these failed to make enough progress and were largely abandoned.
This put the Anglo-French Concorde and the Soviet TU-144 as contenders, with international sales of the Concorde program comparable to the Boeing 707’s launch boom, pushing subsonic aircraft to the brink. At the time, however, the United States was the world’s largest buyer of aircraft, with a huge share of world air traffic. This means that banning supersonic flight in US airspace has effectively destroyed the market for supersonic aircraft.
The prejudicial nature of the provision can be seen in the wording. If the regulation was based on noise levels, it could theoretically solve the problem and develop an aircraft that could fly faster than the speed of sound in the US, but the FAA specifically said the ban was based on speed. Whether the plane produced a boom is irrelevant. It still can’t fly faster than Mach 1.
Today, the ban is still in effect, but times have changed. Since December 31, 2020, the FAA has been working on a periodic review of aircraft noise regulations, with an eye toward modifying the controls for civil supersonic flight. As part of the rethink, NASA’s Quesst program, in partnership with Lockheed Martin, is developing the X-59 experimental aircraft.
The purpose of the X-59 was to test a new aerodynamic hull and wing design that would disperse the shock wave from a supersonic aircraft and deflect most of it upward rather than toward the ground. Once its airworthiness is proven, it will fly at Mach 1.4 on a flight test course with ground sensors and over multiple volunteer communities to assess the aircraft’s sound footprint, comparing it to a sonic thump rather than a roar sound for comparison.
According to NASA, the data will be used to determine acceptable sound levels and how these can be used as the basis for lifting the ban and rewriting FAA regulations.
If successful, it would give the green light to companies around the world investing in the revival of the supersonic passenger transport era.