United Airlines said it would buy ultra-fast jets from Denver-based aerospace company Boom Supersonic, bringing back supersonic passenger travel which died out with the retirement of the Anglo-French Concorde in 2003.

Under the agreement, the airline will purchase 15 of Boom's "Overture" aircraft once they meet United's safety, operating and sustainability requirements, with an option for an additional 35 aircraft.

Overture, a supersonic aircraft with 65 to 88 seats which will be initially priced at business class fares, would cut transatlantic flying time by 50% to about three-and-half hours.

United said the aircraft would be optimized to use 100% sustainable aviation fuel (SAF) from its entry to service, projected to be in 2029.

Currently, commercial aircraft engines are certified to fly with 50% of alternative fuel, with the rest using ordinary kerosene, but available supplies fall far short of that level.

United's head of corporate development, Mike Leskinen, told The Air Current in an interview that the transaction was not a firm order but it involved United taking the lead on "a real aircraft" project.

The aviation publication noted United's move contrasted with the trend in recent decades, of "a desire to fly cheaper not faster".

United said the move reflected a strategy to invest in sustainable air travel.