The US Federal Aviation Administration (FAA) approved new rules in June that could allow supersonic passenger jets to fly over land in the United States again, more than 50 years after Washington effectively banned the practice. The agency's proposal replaces its old speed-based restriction with a noise-based standard and repeals the 1973 ban outright.
Under the new rule, any aircraft flying over US land could produce no more than 0.11 pounds per square foot of sound pressure at the surface, roughly equivalent to a moderate sonic boom. The FAA said it intends to finalize the standard by mid-2027.
Juan Alonso, a professor in the department of aeronautics and astronautics at Stanford University in California, said the change was overdue and welcome, adding that NASA and the American aerospace industry had been pushing for it for a long time.
Even with the door now open, the industry still has a loud problem to solve. When an aircraft exceeds the speed of sound it generates a shock wave that produces a sonic boom, an explosion-like noise on the ground that can startle people and, at times, break windows. Some research suggests the noise levels from booms can even affect human health.
A ban born from Oklahoma City's sonic booms
For six months in 1964, the FAA deliberately subjected Oklahoma City to a daily barrage of sonic booms, 1,253 in total, to gauge public tolerance for supersonic flight. A University of Chicago survey of 3,000 residents found 73% believed they could live with the booms, but the program also triggered lawsuits and around 12,400 complaint calls to the FAA, which ended up compensating some residents for damage to windows and walls.
In 1971, Congress cancelled funding for Boeing's proposed supersonic jet, the 2707, leaving only two rivals in the race to build a supersonic airliner: the European Concorde and the ill-fated Soviet Tupolev Tu-144. In 1973 the FAA effectively banned civilian supersonic flight over US land by barring aircraft from exceeding Mach 1, the sound barrier, to avoid sonic booms.
The Concorde era and its limits
Concorde entered passenger service in January 1976, flown by British Airways and Air France on routes from London to Bahrain and Paris to Rio de Janeiro. It faced immediate opposition over its high operating costs and noise, including sonic booms. Transatlantic flights to New York's John F. Kennedy International Airport only began in late 1977, after the US Supreme Court struck down a ban imposed by the Port Authority of New York and New Jersey over noise concerns.
Unable to fly over land in North America or most of Europe, Concorde ended up serving only New York to Paris and London, plus costly charter flights, mostly to luxury tourist destinations. After a catastrophic 2000 crash that killed 113 people and a brief return to service, it was retired in 2003. Only 14 of the aircraft ever entered operation, and it never had a successor.
Boom Supersonic's boomless cruise
Two rival approaches are now competing to meet the FAA's new noise limits. Boom Supersonic, based in Colorado and specifically named in the FAA's proposal, is using atmospheric physics to keep sonic booms from reaching the ground regardless of aircraft design. NASA, meanwhile, is flying an experimental jet called the X-59, built specifically to soften the boom itself.
Boom's method, known as Mach cutoff, or "boomless cruise," relies on the boom refracting upward due to changes in temperature and wind that affect the local speed of sound. Flown at the right altitude and speed for the atmospheric conditions, it can produce no audible boom at all on the ground. Boom carried out a demonstration flight of the technique in February 2025.
Blake Scholl, who founded Boom Supersonic in 2014, said the technique is about breaking the sound barrier at a sufficiently high altitude, generally above 30,000 feet, using enough computing power and software to calculate the fastest, most efficient quiet speed for any day's weather. He said it is extremely simple for pilots: the company's planned Overture airliner will have a "quiet" button that automatically adjusts speed to fly as fast as possible without an audible boom, and can accelerate further once over open ocean.
Mach cutoff is not a new idea. Lockheed Martin engineers first studied it in the 1960s, and NASA ran tests with FAA approval in the 1970s that found the approach viable. Scholl said some Concorde flights technically achieved Mach cutoff, but pilots did not know how to do it reliably or efficiently. He said Boom did not invent or even discover the physics, but was the first to make it practical, which required real-time computing to calculate speed and altitude and a propulsion system able to fly efficiently at low supersonic speed, something Concorde lacked.
NASA's low-boom X-59
NASA's approach is entirely different and does not depend on navigation or speed but on the aircraft's shape. The X-59 was designed with a "low-boom" profile meant to stop a dense, concentrated shock wave from forming in the first place. It has an unusually elongated nose, an extremely smooth underside and no forward-facing windows; the pilot instead relies on a 4K ultra-high-definition screen in the cockpit that digitally recreates the outside view. NASA says the design should let the aircraft produce a thump comparable to a car door closing about 6 meters away, rather than a loud boom.
Peter Coen, mission integration manager for NASA's Quest mission, which is developing the X-59, said any aircraft in flight produces several shock waves of different intensities along its fuselage, at the nose, cockpit and engine intake, which normally merge into what he calls a "stable system" of two abrupt shock waves, one at the nose and one at the tail, that create an intense sonic boom. He said the design goal is to make those shock waves roughly equal in intensity and evenly spaced along the fuselage, so they still merge but so slowly that the system reaches the ground before fully combining, producing multiple weaker waves that the atmosphere disperses further, resulting in a single gradual thump on the ground rather than a sudden bang.
NASA's ultimate goal is to gather enough data for the International Civil Aviation Organization to set new global sonic boom regulations by 2031. Coen said that for supersonic flight to be economically attractive to major airlines, the solution must allow unrestricted speeds over land, not just over water, which is what the Quest mission is working toward with the X-59.
After several delays, the X-59 made its first flight in late 2025 and reached supersonic speed for the first time in June. It has since flown supersonic twice more, reaching a top speed of Mach 1.4. Coen said the next step, planned for later this year, is to fly faster still and take precise measurements of the shock waves and noise levels the aircraft produces.
Once that data is collected, NASA will move to community testing that closely mirrors the 1964 Oklahoma City program. Coen said the goal is to understand how people react to a sound they do not normally hear, with the key difference that laboratory and preliminary tests suggest the X-59's sound is inaudible or does not provoke a negative reaction. He said the plan is to gradually introduce louder sounds to find the point at which a sonic boom shifts from acceptable to unacceptable.
Prototype or science experiment?
Scholl was sharply critical of NASA's Quest program, calling it a waste of taxpayer money because of how it would need to scale. He said NASA built a plane he believes can demonstrate a few isolated, extremely quiet booms, but that scaled up to an airliner it would be as long as a football field, calling it a science experiment and saying he does not see how it becomes a real aircraft.
Coen pushed back, saying the X-59 was never meant as an airliner prototype but as a way to collect data on quiet flight. He said that as an aircraft grows to airliner size there is more volume to work with, the nose would take a different shape, and it would be large enough to push the cockpit and passenger cabin into that section.
NASA and Boom have collaborated once, during one of the XB-1's supersonic flights, when NASA provided reference points for Boom to photograph the aircraft as it broke the sound barrier. But NASA currently has no plans to study Mach cutoff using the X-59.
A NASA spokesperson told CNN that although the agency conducted extensive Mach cutoff testing in the past, the X-59 was designed to produce a sonic boom at its cruise speed and altitude on every flight. The spokesperson said the low-boom design and Mach cutoff are not competitors but different approaches to commercial supersonic travel over land.
Coen said the good news for Boom is that it does not need to design its aircraft shape around Mach cutoff, but the technique has real limits. An aircraft using Mach cutoff can typically travel only slightly faster than sound, around Mach 1.1, some 30% to 40% faster than today's airliners, though Boom says the phenomenon is possible up to Mach 1.3. Coen said it will not work in all weather because it depends heavily on the atmosphere's temperature and wind patterns, so on some days the cutoff speeds simply will not be flyable.
Still, he said the FAA's new rules and the Mach limit create an opening to reintroduce supersonic flight, calling it an important step toward wider adoption. He said he expects the next generation of supersonic aircraft to incorporate quiet boom-shaping technology and eliminate the need for Mach-limited flight altogether, allowing maximum cruise speed over both land and water, a nod to what NASA is pursuing with the X-59.
Overture's passenger ambitions
During its two supersonic flights, Boom's XB-1 hit the Mach cutoff threshold six times, though the company has not released observational data from those flights. Scholl said Mach cutoff was not part of the original plan and was discovered during flight testing.
Boom originally planned to launch transoceanic flights and outsource engine development. After every major aircraft manufacturer declined to build an engine, judging the venture too risky and too niche, the company is now developing its own engine in-house and plans to start with routes within the continental United States.
The XB-1, a single-engine aircraft, became the first jet developed by a private company to break the sound barrier when it reached the Mach limit. Boom retired the aircraft after just two supersonic flights.
Boom is now building a pre-production prototype of its planned Overture airliner, which the company says could eventually carry 60 to 80 passengers at speeds up to Mach 1.7 over water, twice the speed of today's airliners, cutting flight time on routes such as New York to Los Angeles to 3.5 hours. Scholl said the aircraft could be ready for commercial flights within up to four years.
Fuel, cost and what comes next
Alonso said that because it is far easier to design an aircraft without a low-boom shape, Mach cutoff could allow supersonic flights to be introduced more quickly. But he said the concept cannot deliver the true promise of supersonic travel, which he said is eventually reaching Mach 2 or even Mach 2.5, speeds at which a low-boom shape becomes essential.
Mach cutoff also increases fuel consumption, Alonso said, because engines are not in their ideal efficiency range at those speeds, and the technique requires careful management of speed, altitude, wind, temperature and humidity. He nonetheless called Mach cutoff perfectly viable.
Boom says the Overture will burn up to three times more fuel than current airliners, and that it is designed to run entirely on sustainable aviation fuel (SAF), an alternative to fossil fuels made from cooking oil and agricultural waste that the International Air Transport Association says cuts carbon emissions by an average of 80%. SAF adoption across the aviation industry has been slow, however; even though most emissions-reduction plans depend on it, production is expected to fall short year after year, and SAF still accounts for less than 1% of total aviation fuel use.
Although the low-boom shape used on the X-59 is unlikely to be practical for a large airliner and was not designed for any specific aircraft class, Alonso believes its design principles could more easily apply to smaller supersonic jets, in the range of business jets carrying 15 to 20 passengers. He called it an incredible demonstration of something that could have a tremendous impact on a class of aircraft different from the one Boom Supersonic is targeting.
It remains unclear whether Mach cutoff and low-boom design will end up coexisting or whether one will make the other obsolete. Scholl said the world is not necessarily heading toward a boom-free future for supersonic travel. He said he expects people to discover that even a full sonic boom is not a real problem, noting that he has heard several sonic booms and that the vast majority cause no major disruption. He said there could be a second wave of deregulation allowing non-disruptive sounds, since people do not live in a perfectly silent environment and already tolerate storms, adding that trading a bit of noise for more speed seems like a good deal, one the industry can address when the time comes.
