United Airlines plans to transform the friendly sky into ultra-fast sky with supersonic jets.

The airline announced Thursday that it is buying 15 aircraft from Boom Supersonic with the option to buy 35 more at some point.

Boom’s first commercial supersonic jet, the Overture, has not yet been built or certified. It aims to launch passenger service in 2029 with an aircraft that could fly at Mach 1.7 and cut some flight times in half. This means that a flight from New York to London, which normally takes seven hours, would only take 3½ hours.

A rendering of a United Supersonic Jet

Source: United Airlines

“Boom’s vision for the future of commercial aviation, combined with the world’s strongest network in the industry, will give business and leisure travelers access to a great flying experience,” said Scott Kirby, United CEO, in a press release announcing the deal.

Although the terms of sale were not disclosed, the companies anticipate that the transaction will bring immediate benefits.

Since its inception in 2014, Denver-based Boom Supersonic has raised $ 270 million in capital and grown to 150 employees. For founder and CEO Blake Scholl, winning a firm contract with an old airline confirms his vision of bringing back supersonic flights.

The supersonic Concorde flew commercial flights from 1976 to October 2003.

“The world’s first purchase agreement for carbon-free supersonic aircraft is an important step towards our mission to create a more accessible world,” said Scholl in a statement.

For United, ordering boom supersonic jets fits in with the strategy Kirby has outlined since he took office a year ago.

United Airlines CEO Scott Kirby

Chip Somodevilla | Getty Images

Kirby is aggressively trying to develop opportunities for the airline. Earlier this year, United acquired a stake in eVTOL start-up Archer Aviation and worked with Mesa Airlines to order 200 short-haul electric aircraft. It did so after United announced a multi-million dollar investment in a carbon capture startup and pledged to be carbon neutral by 2050.

Part of what made buying supersonic jets attractive to United is Boom’s plan to power the planes with engines that run on sustainable aviation fuel.

A rendering of a United Supersonic Jet

Source: United Airlines

However, it remains to be seen whether Boom’s plan to bring back supersonic airliners will get underway.

The company plans to make its maiden flight with a demonstrator jet called the XB-1 later this year. If things go as planned, Boom will start producing the overture in 2023 and make its maiden flight in 2026. The ultimate hurdle will be certification from regulatory agencies, including the Federal Aviation Administration.

In this case, United expects to target long-haul international flights between major cities around the world such as San Francisco to Tokyo and New York to Paris.

Mike Leskinen, United’s vice president of corporate development, said the overture could dramatically change some of the airline’s busiest international routes. “If we can cut the time it takes to fly from the US east coast to certain cities in Europe and do it with lower emissions, we think it will be very attractive,” he said.