Boom Technology recently lost its supersonic jet engine partner, Overture, and other major engine manufacturers are also not interested in the project, reports Engadget.

After Boom signed a preliminary agreement with Rolls-Royce for supersonic jet engines in 2020, the latter announced last week that it had left the project. Now other major jet engine manufacturers, including Pratt & Whitney, GE Aviation, Honeywell and Safran Aircraft Engines have said they are not yet interested in supersonic aircraft. Boom assure that the project is still ongoing and that they will soon announce a partner on the engine.

“We can reconfirm our intention to announce Boom’s selected engine partner and transformational approach for reliable, cost-effective, and sustainable supersonic flight, later this year,” Boom said.

The company recently received an order for 20 planes from American Airlines and 15 from United, plans to build a plant in California and complete the supply of planes for passenger transportation by 2029.

“After careful consideration, [we] have determined that the commercial aviation supersonic market is not currently a priority for us and, therefore, will not pursue further work on the program at this time,” Rolls-Royce announced in turn.

The International Civil Aviation Organization (ICAO) recently condemned supersonic travel, saying in a report that it would use 7-9 times more fuel per passenger per kilometer than subsonic jets. In response, Boom said it offsets carbon emissions by using sustainable aviation fuel (SAF). However, the ICAO report said that using the scarce SAF fuel would be a poor solution, given its high burn rate compared to a conventional jet.