FT. WORTH, Texas: American Airlines has become the second major U.S. airline to bet on ultra-fast passenger travel, after signing an agreement to purchase as many as 20 jets from aircraft maker Boom Supersonic.

However, the jets must still meet American’s safety, operating and sustainability requirements. In 2021, United Airlines agreed to buy 15 Boom Overture aircraft.

In an interview, Boom Chief Executive Blake Scholl said the American Airlines deal brings the company’s order book to 130 airplanes, valued at about $26 billion, including options.

Officials said American also has an option to purchase 40 more of the four-engine Overture jets, which can fly from Miami to London in just under five hours, cutting the nearly nine-hour flight time between the cities by about half, with a capacity of 65 to 80 passengers.

Matt Miller, American Airlines spokesperson, said considering the aircraft is not expected to serve passengers until 2029, it was too early to discuss ticket prices.

Environmentalists have criticized supersonic jets for burning more fuel per passenger than subsonic planes.

Designed to run fully on sustainable aviation fuel or a blend, the Overture will be rolled out of Boom’s Greensboro, North Carolina factory in 2025, with test flights being planned for 2026.

However, Third Bridge senior analyst Christopher Raite warned that the delay in conducting test flights for Boom’s other jet, the XB-1, suggests a similar delay in the delivery of the Overture.