<p>On 8 February 1933, Boeing flew the prototype of a new civil airliner which was identified by the company as its Model 247. This had derived via the design of the single-engined civil Model 200 Monomail and the twin-engined Model 214 (US Army designation B-9) bomber, each of which had a cantilever monoplane wing.
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<p>A revolutionary aircraft, it has since become regarded as a prototype for the modern airliner, for it was a clean cantilever low-wing monoplane of all-metal construction with twin-engined powerplant, retractable landing gear, and accommodated a pilot, co-pilot, stewardess and 10 passengers. With one engine inoperative it could climb and maintain altitude with a full load, and introduced a new feature for a civil transport aircraft by being equipped with pneumatic de-icing boots on wing, tailplane and fin leading edges to prevent ice accretion from reaching a dangerous level.
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<p>Sixty examples of the Model 247 were ordered 'off the drawing board' to re-equip the Boeing Air Transport System, shortly to become a major limb of United Air Lines, and another 15 were ordered subsequently for companies or individuals. The one built for Roscoe Turner and Clyde Pangborn (to compete in the England-Australia 'MacRobertson' air race of 1934) was provided with fuselage fuel tanks instead of the standard airline cabin equipment, and introduced NACA engine cowlings (to reduce drag) and controllable-pitch propellers with optimum settings for take-off and cruising performance. These improvements were incorporated retrospectively on most airline Model 247s, thus elevating them to Model 247D standard.
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<p>When the USA became involved in World War II in late 1941, these Model 247Ds remained in airline use, and 27 of them were impressed for service with the USAAF under the designation C-73. It had been anticipated that they could be used for the carriage of cargo and troops, but it was discovered that the cabin doors were too small for this purpose. Instead, they were deployed to ferry aircrew and, later in the war, were used for training. In service they were provided with more powerful engines than the standard civil 550-hp (410-kW) Pratt & Whitney Wasp S1H-1G radials. When no longer required at the war's end they were returned to civil airline service.
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<hi style=hdr1>Specification</hi>
<list style=aflst>
<item><hi format=bold>Type:</hi> civil transport aircraft utilized in military role
<item><hi format=bold>Powerplant:</hi> two 600-hp (447-kW) Pratt & Whitney R-1340-AN-1 Wasp radial piston engines
<item><hi format=bold>Performance:</hi> maximum speed 200 mph (322 km/h); cruising speed 189 mph (304 km/h); service ceiling 25,400 ft (7,740 m); range 745 miles (1,199 km)
<item><hi format=bold>Weight:</hi> maximum take-off 13,650 lb (6,192 kg)
<item><hi format=bold>Dimensions:</hi> span 74 ft 0 in (22.56 m); length 51 ft 7 in (15.72 m); wing area 836 sq ft (77.66 m<su>2</su>)
