Explained: In proposed return of supersonic flying, the benefits and concerns

Nearly two decades since the last supersonic passenger flight, of the British-French airliner Concorde, took off, the planes are set to return to the runways by 2029. United Airlines on Thursday announced it was ordering 15 planes with the ability to travel at Mach 1.7, faster than the speed of sound, from the Denver-based startup Boom.

If the deal gets through, the new supersonic “Overture” aircraft will become the world’s fastest commercial airliner, reducing travel time by about half of today’s planes. Travel time from Singapore to Dubai, usually around seven hours, would be reduced to four hours. United Airlines has committed to buy the Boom planes only if they meet certain requirements of safety and sustainability.