United Airlines officials announced a commercial agreement with Denver-based aerospace company Boom Supersonic to add aircraft to its global fleet as well as a cooperative sustainability initiative – a move that facilitates a leap forward in returning supersonic speeds to aviation.

Under the terms of the agreement, United will purchase 15 of Boom’s Overture airliners, once the aircraft meets United’s safety, operating, and sustainability requirements, with an option for an additional 35 aircraft. The companies will work together on meeting those requirements before delivery.

Once operational, Overture is expected to be the first large commercial aircraft to be net-zero carbon from the start, optimized to run on 100% sustainable aviation fuel (SAF). It’s slated to roll out in 2025, fly in 2026, and expected to carry passengers by 2029. United and Boom will also work together to accelerate production of greater supplies of SAF.

“United continues on its trajectory to build a more innovative, sustainable airline and today’s advancements in technology are making it more viable for that to include supersonic planes,” United CEO Scott Kirby said. “Our mission has always been about connecting people and now working with Boom, we’ll be able to do that on an even greater scale.”

Capable of flying at speeds of Mach 1.7 – twice the speed of today’s fastest airliners – Overture can connect more than 500 destinations in nearly half the time. Among the many future potential routes for United are Newark to London in 3.5 hours, Newark to Frankfurt in 4 hours and San Francisco to Tokyo in 6 hours. Overture will also be designed with in-seat entertainment screens, ample personal space, and contactless technology.

“The world’s first purchase agreement for net-zero carbon supersonic aircraft marks a significant step toward our mission to create a more accessible world,” said Blake Scholl, Boom Supersonic founder and CEO. “At speeds twice as fast, United passengers will experience all the advantages of life lived in person, from deeper, more productive business relationships to longer, more relaxing vacations to far-off destinations.”

Overture’s order book, including purchases and options, stands at 70 aircraft, and Boom is working with the United States Air Force for government applications of Overture. XB-1, a demonstrator aircraft, rolled out in 2020, and its net-zero carbon flight test program is underway. The company is backed by world-class investors, including Bessemer Venture Partners, Prime Movers Lab, Emerson Collective and American Express Ventures.

A potential rival in supersonic business jets, Florida-based Aerion Supersonic, shut down May 24 after failing to raise the further capital it needed to bring its supersonic business jet to market.

Aerion had been aiming to begin build a prototype of its AS2 supersonic business jet in 2023, with its first flight scheduled to follow in 2025.