Boom Supersonic is building its own engine after major manufacturers refused to help. Here's what we know about Symphony, which will power the super-speedy Overture jet.

• Boom is trying to build a Supersonic jet that could cross the Atlantic in 3.5 hours.
• Last December, it decided to make its own engine after engine manufacturers refused to help.

Boom — the company building a supersonic aircraft which could go from New York to London in under 4 hours — shared new details about its engine at the Paris Air Show on Tuesday.

Boom is creating an engine called Symphony, which will be built with aerospace partners FTT, StandardAero, and GE Additive — which is known for using 3D printing.

"We are optimizing Symphony for sustainable commercial supersonic flight by designing it to run on 100% SAF [sustainable aviation fuel] from day one," a spokesperson told Insider.

Sustainable aviation fuel is made from sources like cooking oil and waste, and can reduce carbon emissions by up to 80% compared to traditional jet fuel.

Boom CEO Blake Scholl said the airliner "can be powered by a relatively conventional turbofan engine," which has been around for over 60 years.

"Today, this is the class of engines that powers virtually every commercial," he said. "To hit the best performance, economics, and sustainability, Overture needs a turbofan engine specifically optimized for sustained supersonic flight and sustainable performance."

The company is aiming to be net zero by 2025, and Scholl said using sustainable aviation fuel is key to this.

"SAF is truly the best and really only way to rapidly decarbonize aviation," he added.

Scholl also announced that Boom has chosen Jupiter, Florida, as the site for its assembly plant to build the first 40 Symphony engines.

However, there will be another site chosen in the future because Boom will need thousands of engines to meet its expected fleet of hundreds of Overture airliners.

Boom's decision to build its own engine came after all of the major jet-engine manufacturers refused to help. Rolls-Royce used to have a contract with Boom before deciding it didn't want to prioritize commercial supersonic flight.

"As Boom has matured the Overture program, we listened to our partners and customers and learned that applying the current subsonic engine model to our supersonic airliner would not be the most economically sustainable solution," a Boom spokesperson told Insider.

The company is now three and a half years into its 10 year program, and despite any setbacks with the engine, Scholl said he is still confident in Boom's 2029 target for the supersonic airliner to receive FAA certification.

According to Boom, the planemaker has solidified 130 orders and pre-orders from carriers like United Airlines and American Airlines, the former's worth $200 million.