Ten months after its long-delayed first subsonic flight took place last March, Boom Supersonic’s prototype test plane, the XB-1, broke the sound barrier today three times during its twelfth flight. The XB-1 is a smaller-scale demonstration version of the larger Overture airliner Boom wants to eventually build that will carry 64 passengers on supersonic international flights at cruising speeds of up to Mach 1.7, similar to service that the Concorde offered before it retired in 2003.

After taking off from the Mojave Air & Space Port in California, Boom’s chief test pilot, Tristan Brandenburg, flew the XB-1 to an altitude of 34,000 feet before hitting a top speed of Mach 1.1 (around 844 mph) for approximately four minutes. Today’s flight is not only the first time Boom’s demonstrator aircraft broke the speed of sound, it’s also the first time a civil aircraft has gone supersonic. The Concorde was built as a joint venture between the governments of the UK and France, not a private company.

The XB-1 broke the sound barrier two additional times during its return and descent. Today’s test flight took place in airspace known as the Bell X-1 Supersonic Corridor (named after the first plane ever to break the sound barrier) and lasted almost 34 minutes. The 63-foot-long plane is powered by three General Electric J85-15 turbojet engines, but the company plans to develop and build the four engines needed to power the larger Overture airliner on its own after Boom’s partnership with Rolls Royce ended in 2022.

During its initial test flight on March 22, 2024 — originally scheduled to take place in 2021 — the XB-1 achieved a top speed of just 283 mph. The most recent test flight took place earlier this year on January 10th, 2025, when Brandenburg hit a top speed of Mach 0.95 and an altitude of 29,481 feet.

Although its first successful supersonic flight is a milestone for Boom Supersonic, there’s still a lot of development and test flights needed for the company to achieve its current goal of Overture taking its first flight by 2030. As of May 2024, the company has raised over $700 million and has sold 15 supersonic aircraft to United Airlines (with the option to buy 35 more) and 20 to American Airlines.