United Airlines officials announced a commercial agreement with Denver-based aerospace company Boom Supersonic to add aircraft to its global fleet as well as a cooperative sustainability initiative – a move that facilitates a leap forward in returning supersonic speeds to aviation. Under the terms of the agreement, United will purchase 15 of Boom’s Overture airliners, once the aircraft meets United’s safety, operating, and sustainability requirements, with an option for an additional 35 aircraft. The companies will work together on meeting those requirements before delivery. Once operational, Overture is expected to be the first large commercial aircraft to be net-zero carbon...