Supersonic airliners have been the objects of numerous recent and ongoing design studies. Drawbacks and design challenges are excessive noise generation (at takeoff and due to sonic booms during flight), high development costs, expensive construction materials, high fuel consumption, extremely high emissions, and an increased cost per seat over subsonic airliners. Despite these challenges, Concorde was claimed to operate profitably, although that was due to write off of all development and construction costs plus the willingness of passengers to pay high fares.