Capital Airlines Lockheed Constellations. In 1955 they became the first U.S. operator of the British manufactured, four engine Vickers Viscount, the first passenger turboprop airliner. The Viscount propjets were deployed on the flagship Washington-Chicago route and the airline had planned to fly them on expanded service; however, Capital was mostly stymied by the federal Civil Aeronautics Board (CAB). The CAB also refused Capital a requested subsidy. Still, Capital's passenger-miles in 1957 were 88% more than 1955. On November 14, 1956 a Capital pilot reported seeing a blue-white ball in the sky. The pilot, Captain William J. Hull, was a senior captain who
Turboprop Kaman's K-125 synchropter, which used a Boeing T50 turboshaft engine to power it on 11 December 1951. Compared to turbofans, turboprops are most efficient at flight speeds below 725 km/h (450 mph; 390 knots) because the jet velocity of the propeller (and exhaust) is relatively low. Modern turboprop airliners operate at nearly the same speed as small regional jet airliners but burn two-thirds of the fuel per passenger. However, compared to a turbojet (which can fly at high altitude for enhanced speed and fuel efficiency) a propeller aircraft has a lower ceiling. The most common application of turboprop engines in