Boom's supersonic jet is facing a lack of interest from engine suppliers
Manufacturers say supersonic travel is 'tangential' and are focusing on efficiency instead.
Boom Supersonic
United Airlines plans to add 15 Boom Supersonic jets to its fleet
The carrier could end up buying a total of 35 planes from the startup.
Boom unveils the XB-1, its supersonic testbed
The craft is expected to start test flights in 2021.
The Colorado startup dreaming up a return to supersonic flight
Boom Supersonic hopes to test-fly its supersonic plane in 2021.
