American Airlines Group Inc on Tuesday agreed to buy up to 20 ultra-fast jets from Boom Supersonic, with an option to purchase 40 more, becoming the second major U.S. airline to bet on supersonic passenger travel.

American has made a non-refundable deposit on the initial 20 Overture jets, the companies said in a joint statement, without disclosing the size of the deposit.

The era of regular commercial supersonic flights appeared to have ended in 2003 when Concorde, flown by Air France and British Airways, was retired after 27 years of service.

But last year, United Airlines Holdings Inc agreed to buy 15 Boom Overture aircraft after they met certain safety, operating and sustainability requirements. A similar condition was revealed in American Airlines' agreement on Tuesday.

Boom's Overture jet is expected to carry passengers at twice the speed of the fastest commercial aircraft currently available, the company said.

The jet is scheduled to roll out in 2025 and carry its first passengers by 2029, Boom added.

The Allied Pilots Association, which represents pilots of American Airlines, criticized the deal, saying the carrier should instead focus on reducing cancellations and delays which have hit its operations this year.