Initially, some Boeing engineers were skeptical that the winglets, which add weight to a plane, would boost performance, according to Mr. Clark and Boeing officials.
After he installed winglets on his Citation X to make it go even faster, I asked him if he ever throttled back to take advantage of the fuel savings that the winglets gave his airplane.
These winglets, which Cessna says increase fuel efficiency and takeoff and landing performance at higher elevations and on hot days, were previously available as an aftermarket option on the Citation X but come as standard on the new model.