Hubbry Logo
Boeing 247Boeing 247Main
Open search
Boeing 247
Community hub
Boeing 247
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Boeing 247
Boeing 247
Boeing 247
View on Wikipedia
from Wikipedia

The Boeing Model 247 is an early American airliner, and one of the first such aircraft to incorporate advances such as all-metal (anodized aluminum) semimonocoque construction, a fully cantilevered wing, and retractable landing gear.[3][4] Other advanced features included control surface trim tabs, an autopilot and de-icing boots for the wings and tailplane.[5] The 247 first flew on February 8, 1933, and entered service later that year.[6]

Key Information

Design and development

[edit]
The Boeing 247 production line
Early versions had the windshield raked forward, to avoid reflecting light off the cockpit instruments. It was later changed to a backward slope because it reflected landing lights on the ground.

Boeing introduced a host of aerodynamic and technical features into a new commercial airliner building on work with the earlier Monomail (Models 200, 221, 221A) mailplanes and B-9 bomber designs. The Boeing 247 was faster than the best U.S. fighter of its day, the open-cockpit biplane Boeing P-12.[7] The low landing speed of 62 mph (100 km/h) avoided the need for flaps, and pilots learned that at speeds as low as 10 mph (16 km/h), the 247 could be taxied "tail high" for ease of ground handling.[8]

The 247 could fly on one engine. With controllable-pitch propellers, the 247 could maintain 11,500 ft (3,500 m) at maximum gross weight on one engine.[9] Aside from its size, much lower wing loading, and the wing spar obstructing the cabin, many of its features became the norm for airliners, including the Douglas DC-1, before World War II.[6] Originally planned as a 14-passenger airliner powered by Pratt & Whitney R-1690 Hornet radial engines, the preliminary review of the design concept by United Air Lines' pilots had resulted in a redesign to a smaller, less capable configuration, powered by R-1340 Wasp engines.[10][11][12]

One concern of the pilots was that in their view, few airfields could safely take an eight-ton aircraft.[11] They also objected to the Hornet engines, which had a detonation problem when using the available low octane fuel, and suffered from excessive vibration.[13] Pratt & Whitney's chief engineer, George Mead, knew the problem would be resolved eventually,[11] but P&W's president, Frederick Rentschler acquiesced to the airline pilots' demand. The decision created a rift between Mead and Rentschler.[11] Despite the disagreements, the 247 would be Boeing's showcase exhibit at the 1933 Chicago World's Fair.[14]

The slope of the early 247's windshield was reversed from normal. This was a design solution, also used on other contemporary aircraft, to the problem of control panel instrument lights reflecting off the windshield, but the reversed windshield reflected ground lights instead, especially during landings, and it also increased drag.[15][16] By the introduction of the 247D, the windshield was sloped normally, and the glare was resolved with a glarescreen extension over the panel.[17]

Boeing incorporated design elements to enhance passenger comfort, such as the thermostat controlled, air conditioned, and noise-proofed cabin. The crew included a pilot and copilot, as well as a flight attendant (then known as a "steward"), who could tend to passenger needs.[18] The main landing gear did not fully retract; the wheels extended slightly below the nacelles, typical of designs of the time, as a means of reducing structural damage in a wheels-up landing. The tailwheel was not retractable. While the Model 247 and 247A had speed-ring engine cowlings and fixed-pitch propellers, the Model 247D incorporated NACA cowlings and variable-pitch propellers.[19]

Operational history

[edit]
United Airlines crew members and employees stand in front of a Boeing 247
A Boeing 247D in its MacRobertson Air Race markings, c. 1934: Note the dramatic pose in this fanciful 1935 illustrated card art.
A stewardess points to the markings on a Boeing 247 that commemorate finishing third in the MacRobertson Air Race.

As the 247 emerged from its test and development phase, the company further showcased its capabilities by entering a long-distance air race in 1934, the MacRobertson Air Race from England to Australia. During the 1930s, aircraft designs were often proven in air races and other aerial contests. A modified 247D was entered, flown by Colonel Roscoe Turner and Clyde Pangborn.[20] The 247, race number "57", was essentially a production model, but all airliner furnishings were removed to accommodate eight additional fuselage fuel tanks.[21] The MacRobertson Air Race attracted aircraft entries from all over the globe, including both prototypes and established production types, with the grueling course considered an excellent proving ground, as well as an opportunity to gain worldwide attention. Turner and Pangborn came in second place in the transport section (and third overall), behind the Boeing 247's eventual rival, the new Douglas DC-2.[22]

Being the winner of the 1934 U.S. Collier Trophy for excellence in aviation design, the first 247 production orders were earmarked for William Boeing's airline, Boeing Air Transport.[21] The 247 was capable of crossing the United States from east to west eight hours faster than its predecessors, such as the Ford Trimotor and Curtiss Condor. Entering service on May 22, 1933, a Boeing Air Transport 247 set a cross-country record of 19+1⁄2 hours on its San Francisco to New York City inaugural flight.[2][23]

Boeing sold the first 60 247s, an unprecedented $3.5 million order, to its affiliated airline, Boeing Air Transport (part of the United Aircraft and Transport Corporation, UATC), at a unit price of $65,000.[6][9] TWA (Transcontinental & Western Air) also ordered the 247, but UATC declined the order, which resulted in TWA President Jack Frye setting out requirements for a new airliner and funding Don Douglas to design and build the Douglas DC-1 prototype. Douglas eventually developed the design into the DC-2 and DC-3.[6]

The Boeing design had been the first to enter series production, but the 247 proved to have some serious deficiencies. Airlines considered its limited capacity a drawback, since it carried only 10 passengers, in five rows with a seat on each side of the aisle, as well as a stewardess. Compared to the more spacious DC-2 and later DC-3, the passenger count was too few to make it a commercially viable airliner.[22] Another feature influencing passenger comfort was that the 247's main wing spar ran through the cabin, so persons moving through the cabin had to step over it.[24] The Lockheed Model 10 Electra had a similar configuration, and while it was a more compact design, the Electra managed to carry the same number of passengers at a slightly better overall performance, and at a lower cost-per-mile.[22]

Seventy-five 247s were built; Douglas collected 800 civil orders for DC-3s before the Pearl Harbor attack, and produced over 10,000 DC-3s, including wartime production of C-47s, while the rival Lockheed Electra "family" was eventually to reach over 3,000 in its various civil and military variants. Boeing Air Transport bought 60 examples, United Aircraft Corp. 10, Lufthansa ordered three, but only two were delivered,[25][26] and one went to a private owner in China. While the industry primarily standardized on Boeing's competitors, many of United's aircraft were later purchased by Western Air Express at "bargain-basement prices".[27]

No. 121 RCAF Squadron Boeing 247D, c. 1939

The 247 remained in airline service until World War II, when several were converted into C-73 transports and trainers. The Royal Canadian Air Force's 121 Squadron operated seven 247Ds as medium transports during the early part of the war.[28] One of these aircraft was donated to the Royal Air Force (RAF) for radar testing, where it was renumbered DZ203. DZ203 was passed among several units in the RAF before being used to make the world's first fully automatic blind landing on 16 January 1945.[29]

Warlord "Young Marshal" Zhang Xueliang ordered two Boeing 247Ds for his air force. He used one of them, named Bai-Ying (White Eagle), during the Xi'an incident in 1936, during which he flew into the opposing Nationalist army's camp at Sian (now rendered as Xi'an) under a secret truce, and had their leader, Generalissimo Chiang Kai-shek, arrested, ending the civil war between the Communist and Nationalist armies, so they could fight together against the Japanese invaders.[30]

A number of specially modified variants included a Boeing 247Y appropriated from United for Air Corps use as a test aircraft fitted with two machine guns in the nose. The same installation later was fitted to a 247Y owned by Generalissimo Chiang Kai-shek. This aircraft also featured a Colt .50 in (12.7 mm) machine gun in a flexible mount.[31] A 247D purchased by the British RAF became a testbed for instrument approach equipment and received a nonstandard nose, new powerplants, and fixed landing gear.[32] Some 247s were still flying in the late 1960s as cargo transports and business aircraft.[22]

The Turner/Pangborn 247D still exists. Originally flown on September 5, 1934, it was leased from United Airlines for the 1934 MacRobertson Air Race and returned to United, where it served in regular airline service until 1937. Subsequently, the 247D was sold to the Union Electric Company of St. Louis for use as an executive transport. The Air Safety Board purchased the aircraft in 1939 and it remained in use for 14 years before it was donated to the National Air and Space Museum, Washington, DC. It is displayed today with two sets of markings, the left side is marked as NR257Y, in Colonel Turner's 1934 MacRobertson Air Race colors, while the right side is painted in United Airlines livery, as NC13369.[20]

Variants

[edit]
Boeing 247 prototype at Boeing Field, circa 1933
A 247 in the 1950s

[33]

Model 247
Twin-engined civil transport airliner, initial production version
247A
Powered by new 625 hp (466 kW) P&W Wasp, on special order for Deutsche Luft Hansa in 1934
247E
This designation was given to the first Boeing 247 aircraft, it was used to test a number improvements that were later incorporated into the Boeing 247D.
247D
Original one-off was a race aircraft designed for the MacRobertson Air Race; use of Hamilton Standard variable-pitch propellers allowed for a 7 mph (11 km/h) gain; the 247D configuration incorporated in production series bearing the same name.
247Y
Armed version, one exported to China, second used for trials
C-73
Designation for Boeing 247D airliners impressed into military service in USAAF, 27 in total
Model 280
Proposed development of Boeing 247 with 14 seats and 700 hp (520 kW) P&W Hornet engines

Operators

[edit]

Civil operators

[edit]
A C-73 during World War II
 Brazil
Canada
 Republic of China
  • Private owner operated one aircraft.
 Colombia
Germany
United States

Military operators

[edit]
Canada
 United Kingdom
United States

Accidents and incidents

[edit]
October 10, 1933
United Air Lines 247, NC13304 (c/n 1685), was probably the first victim of sabotage of a commercial airliner. The aircraft, en route from Cleveland to Chicago, was destroyed by a nitroglycerin-based explosive device over Chesterton, Indiana.[34] All seven on board were killed.
November 9, 1933
A Pacific Air Transport 247, NC13345 (c/n 1727), crashed on takeoff after the pilot became disoriented in fog and low visibility; four of ten on board died.[35]
November 24, 1933
A National Air Transport 247, NC13324 (c/n 1705), was being ferried from Chicago to Kansas City when it crashed near Wedron, Illinois, killing all three crew.[36]
February 23, 1934
A United Air Lines 247, NC13357 (c/n 1739), crashed in Parley's Canyon in fog near Salt Lake City, killing all eight on board.
December 20, 1934
United Air Lines Flight 6, a 247 (NC13328, c/n 1709), struck a tree and crashed near Western Springs, Illinois, due to carburetor icing; all four on board survived. The aircraft involved was repaired and converted to 247D standard in July 1935 and returned to service;[37] the aircraft was pressed into USAAF service in 1942 and redesignated as C-73 with tail number 42-57210. The aircraft was damaged in a wind storm at Duncan Field, Texas, on August 30, 1942, and was written off.[38]
March 24, 1935
The sole 247 operated by Lufthansa (D-AGAR, c/n 1945) was damaged beyond economical repair in a collision with an Air France aircraft on the ground at Nuremberg and then scrapped[26]
September 1, 1935
Western Air Express 247, NC13314 (c/n 1695), was being ferried from Burbank, California, to Saugus, California, when it struck high tension power lines after takeoff, killing all three on board.[39]
October 7, 1935
United Airlines Flight 4, a 247D (c/n 1698), went down about 10 mi (16 km) west of Cheyenne, Wyoming due to pilot error. Three crew and nine passengers killed, there were no survivors.[40]
October 30, 1935
United Air Lines Boeing 247D, NC13323 (c/n 1704), crashed during an instrument checkflight near Cheyenne, killing the four crew members aboard.[41]
December 15, 1936
Seven died when Western Air Express Flight 6, a 247D,[42] en route from Burbank, California, to Salt Lake City via Las Vegas, crashed just below Hardy Ridge on Lone Peak in Utah.[43] The major parts of the aircraft were hurled over the ridge and fell over 1,000 ft (300 m) into a basin below.[42]
December 27, 1936
United Airlines Trip 34, a 247D (c/n 1737), crashed at the head of Rice Canyon, Los Angeles County, California, due to pilot error; all 12 on board died.
January 12, 1937
Western Air Express Flight 7, a 247D (c/n 1696) flight from Salt Lake City to Burbank, crashed into a mountain near Newhall, California, killing five. Among the dead was Martin Johnson of Martin and Osa Johnson fame (adventurers, authors, and documentary filmmakers).[44]
August 13, 1937
A 247 being operated by the Luftwaffe's proving ground at Rechlin (formerly D-AKIN of Lufthansa, c/n 1944) crashed at Hannover, Germany, during a test flight,[26] killing seven of eight on board. The aircraft was being used as a testbed for an experimental autopilot.
March 13, 1939
A SCADTA 247D, C-149, crashed near Manzanares, Caldas, Colombia, killing all eight on board.[45]
February 27, 1940
A SCADTA 247D, C-140, struck El Mortino mountain near Tona, Santander, Colombia, killing all 11 on board.[46]
July 30, 1942
A Northwest Airlines C-73, 42-68639 (c/n 1717, former NC13335), crashed and burned on takeoff from Wold Chamberlain Field, near Minneapolis, Minnesota, killing all 10 on board.[47]

Surviving aircraft

[edit]
Boeing 247D at the National Air and Space Museum showing United Air Lines markings in this view.[20]
c/n 1699, CF-JRQ
Exhibited in Canada Aviation and Space Museum, Ottawa. Donated to the museum in 1967 by California Standard Oil of Calgary, Alberta.[48]
c/n 1722, N18E
Exhibited in the National Museum of Science and Industry, Wroughton, UK
The Boeing 247 at the Museum of Flight in the city of Tukwila, just south of Seattle
c/n 1729, N13347
Static display, flown after restoration at the Museum of Flight Restoration Center, Paine Field, Snohomish County, Washington, USA, to the Museum of Flight main facility on 26 April 2016 where it was subsequently installed in that museum's Air Park.[49]
c/n 1953, NC13369 / NR257Y
Exhibited in the Hall of Air Transportation at the National Air and Space Museum, Washington, D.C., USA, with United Air Lines colors and registration as NC13369 on its right fuselage and wing and as NR257Y with MacRobertson Air Race markings on its left side.[20]

Specifications (Boeing 247D)

[edit]

Data from Boeing aircraft since 1916[50]

General characteristics

  • Crew: Three
  • Capacity: 10 passengers + baggage and 400 lb (181 kg) of mail
  • Length: 51 ft 7 in (15.72 m)
  • Wingspan: 74 ft 1 in (22.58 m)
  • Height: 12 ft 1.75 in (3.7021 m)
  • Wing area: 836.13 sq ft (77.679 m2)
  • Airfoil: Boeing 106B[51]
  • Empty weight: 8,921 lb (4,046 kg)
  • Max takeoff weight: 13,650 lb (6,192 kg)
  • Fuel capacity: 273 US gal (227 imp gal; 1,030 L)
  • Powerplant: 2 × Pratt & Whitney R-1340 S1H1-G Wasp 9-cylinder air-cooled radial piston engines, 500 hp (370 kW) each at 2,200 rpm at 8,000 ft (2,400 m)
  • Propellers: 2-bladed variable-pitch propellers (3-bladed propellers shown in line drawing)

Performance

  • Maximum speed: 200 mph (320 km/h, 170 kn)
  • Cruise speed: 189 mph (304 km/h, 164 kn) at 12,000 ft (3,700 m)
  • Range: 745 mi (1,199 km, 647 nmi)
  • Service ceiling: 25,400 ft (7,700 m)
  • Absolute ceiling: 27,200 ft (8,291 m)
  • Rate of climb: 1,150 ft/min (5.8 m/s)

Notable appearances in media

[edit]
Main article: Aircraft in fiction § Boeing 247

See also

[edit]

Related development

Aircraft of comparable role, configuration, and era

Related lists

Notes

[edit]

Bibliography

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Boeing 247

View on Grokipedia
from Grokipedia

The Boeing 247 was a twin-engine all-metal monoplane airliner developed by Boeing Airplane Company and first flown on February 8, 1933, marking it as the inaugural modern passenger aircraft through innovations including a semi-monocoque fuselage, retractable landing gear, and de-icing equipment for wings and propellers. Powered by two Pratt & Whitney R-1340 Wasp radial engines, the Model 247D variant cruised at approximately 170 mph and accommodated up to 10 passengers plus crew in a pressurized cabin, enabling faster transcontinental flights compared to tri-motor competitors like the Ford Trimotor. Primarily ordered by United Air Lines, a subsidiary controlled by Boeing, the aircraft was initially withheld from sale to competitors to secure United's dominance on lucrative air mail routes, a strategy that fueled the 1934 Air Mail scandal when government investigations revealed collusion among manufacturers and airlines, leading to contract cancellations, antitrust scrutiny, and Boeing's divestiture of United. Only 75 units were produced between 1933 and 1934, limiting its commercial proliferation as rivals like the Douglas DC-2 offered greater capacity at similar speeds, yet its design influenced subsequent airliners and saw military adaptations as transports during World War II.

Development

Origins and Initial Design

The Boeing 247 originated from efforts by the Boeing Airplane Company in early 1932 to develop a successor to the carrier's aging biplane airliners, such as the Model 40 and Model 80, amid growing demand for faster and more efficient passenger transport. As part of the holding company, Boeing prioritized designing an advanced aircraft tailored for United Air Lines, with President Philip G. Johnson placing an order for 60 units in March 1932 to secure exclusivity and accelerate modernization of the fleet. Initial design proposals explored various configurations, including a and a high-wing twin-engine layout, before engineers settled on a low-wing, twin-engine to optimize speed, , and structural efficiency using all-metal construction. The prototype, designated as the Boeing 247 with registration X13301 and constructor's number 1682, incorporated two or Twin Wasp radial engines rated at approximately 550 horsepower each, cantilevered wings, and retractable to reduce drag and enhance performance. This design drew from prior Boeing projects like the Model 200 Monomail and B-9 bomber, adapting military-derived for commercial use to achieve cruising speeds exceeding 180 miles per hour, significantly outpacing contemporaries. The prototype achieved its maiden flight on February 8, 1933, from in , validating the innovative features including controllable-pitch propellers, wing de-icing boots, and an system, which together marked a departure from fabric-covered biplanes toward streamlined, all-metal airframes capable of reliable high-altitude operations. These elements positioned the 247 as the first truly modern , emphasizing safety through single-engine service ceiling capabilities and passenger comfort in a cabin accommodating up to 10 passengers and three members.

Technical Innovations and Engineering Challenges

The Boeing 247 incorporated pioneering engineering features that advanced design in the early 1930s. Its all-metal fuselage and low-wing configuration eliminated drag-inducing external wires and struts prevalent in airliners, enabling a streamlined profile with a gross weight of 16,000 pounds in initial variants. Powered by twin Wasp S3H1 supercharged radial engines each delivering 550 horsepower, the aircraft achieved a cruise speed of 165 mph and a service ceiling of 25,400 feet, outperforming tri-motor contemporaries like the by approximately 50 percent in speed. Retractable main , hydraulically actuated, further minimized aerodynamic drag compared to fixed-gear designs. Subsequent refinements in the 247D variant introduced controllable-pitch propellers via hydraulic mechanisms from , allowing optimized thrust for takeoff and cruise, alongside pneumatic de-icing boots on leading edges of wings and tail surfaces to mitigate ice accumulation—a first for production airliners. Control surface enabled precise in-flight adjustments, reducing pilot workload, while early integration of an system enhanced stability on long routes. These elements collectively demonstrated forward-thinking and systems integration, with the 247 capable of single-engine flight at altitudes up to 11,500 feet, a threshold unmatched by rivals at the time. Engineering challenges arose from internal Boeing conflicts and developmental constraints. Chief engineer R.J. Minshall advocated for a conservative limited to existing production scales, but broader debates pitted —favoring a compact 10-passenger layout tailored to United Air Lines' specifications—against engineers pushing for an expandable 18-seat model with greater gross weight up to 16,000 pounds for future-proofing. This compromise resulted in a underpowered for economic viability, as the fixed 12,000-pound gross weight restricted and range, yielding only marginal profitability on short routes. Weight penalties from new features like de-icing boots and variable-pitch propellers sparked resistance, with engineer Monty Monteith citing added mass as a performance risk, delaying full implementation until the 247D. Operational deficiencies highlighted rushed integration issues, including absent cutoff switches for motors, which caused frequent burnouts from prolonged extension cycles, and an initial backward-sloping that reflected ground lights into the , necessitating post-production glareshields. Evolving from the underpowered prototype, the 247 grappled with immature technologies like variable-pitch propellers, which were not fully reliable until later refinements, contributing to higher maintenance demands. These factors, compounded by the aircraft's limited capacity, underscored how corporate priorities over engineering scalability curtailed its long-term dominance, as evidenced by its swift obsolescence against the larger Douglas DC-3.

Production and Commercialization

Manufacturing and Sales Strategy

The Boeing 247 was manufactured at the Boeing Airplane Company's plant in Seattle, Washington, where assembly lines produced the all-metal, twin-engine airliners using advanced fabrication techniques for the era, including construction and integration. Production began following the prototype's first flight on February 8, 1933, with the first delivery to United Air Lines occurring in May 1933. In total, 75 aircraft were built between 1933 and 1934, each costing approximately $65,000. Boeing's sales strategy centered on prioritizing its affiliate, United Air Lines—a subsidiary within the United Aircraft and Transport Corporation (UATC) holding company—to secure a dominant market position. United placed an initial order for 60 aircraft, which effectively monopolized production capacity and granted the airline exclusive access to the model for an extended period, preventing competitors like Trans World Airlines (TWA) from purchasing units until United's fleet requirements were fulfilled. This approach aimed to leverage the 247's technological superiority—such as its speed, range, and all-weather capabilities—to provide United with a competitive edge in transcontinental routes. Of the 75 produced, United Air Lines operated 60, while the remaining units went to (10), , and private owners. The exclusivity clause drew criticism for stifling , contributing to broader antitrust of UATC's integrated operations, though it initially succeeded in positioning the 247 as United's for non-stop coast-to-coast service. Subsequent sales to non-U.S. operators highlighted Boeing's pivot after fulfilling the primary commitment, but the strategy underscored the era's trend toward vertically integrated conglomerates.

Exclusivity Clauses and Market Exclusion Attempts

Boeing Airplane Company, as a subsidiary of United Aircraft and Transport Corporation (UATC), developed the Model 247 primarily for its affiliated airline, United Air Lines, which placed an initial order for 60 aircraft in 1933 at a cost of approximately $3.5 million. As part of this arrangement, Boeing agreed not to offer the 247 for sale to any competing U.S. airlines until United's full order was fulfilled, effectively granting United temporary exclusivity over the aircraft's advanced features, including its all-metal construction, retractable landing gear, and twin-engine configuration capable of carrying 10 passengers at speeds up to 200 mph. This clause stemmed from UATC's integrated structure, where manufacturing and operations were vertically aligned to prioritize internal efficiency and competitive dominance in key routes, such as transcontinental airmail and passenger services. The exclusivity provision excluded rivals like () from acquiring the 247, despite their interest in its superior performance over existing biplanes like the . 's repeated requests were denied, forcing the carrier to solicit alternative designs from manufacturers such as , which responded with the DC-1 prototype in 1933 and the production DC-2 in 1934. Similarly, other airlines, including American Airways, faced , prompting independent development efforts that accelerated innovation in the sector but diluted Boeing's initial market lead. Boeing's strategy reflected a calculated attempt to leverage the 247's technological edge—deemed the first modern airliner—for United's route monopoly advantages, particularly following UATC's 1931 consolidation of carriers with exclusive Post Office contracts. By mid-1934, after delivering United's 60 units, Boeing began offering the 247 to external buyers, but the delay had already spurred competitors' advancements, with the DC-2 outselling the 247 in some markets due to its larger capacity for 14 passengers. This market exclusion tactic, while short-term, highlighted UATC's broader approach to , where equipment divisions supplied affiliates preferentially to consolidate control over air . Critics, including rival carriers, argued it stifled in an industry reliant on rapid technological diffusion, though Boeing maintained the policy protected substantial R&D investments exceeding $1 million in the 247's design. Ultimately, only 75 civilian 247s were produced, limiting its commercial proliferation compared to successors like the DC-3.

Regulatory and Economic Context

Antitrust Actions Against United Aircraft and Transport

In response to revelations of collusion in airmail contract bidding during the , Congress passed the Air Mail Act of 1934 (Black-McKellar Act) on June 12, 1934, which prohibited aircraft manufacturers from operating or holding significant interests in commercial airlines to prevent anti-competitive practices and ensure fair bidding. This legislation directly targeted conglomerates like (UATC), a formed in 1929 that integrated Airplane Company, engines, , and United Air Lines, giving it control over roughly 60% of U.S. airmail routes and substantial manufacturing dominance. UATC's vertical integration enabled preferential treatment, such as exclusive access to advanced aircraft like the Boeing 247 for its airline subsidiary while restricting sales to competitors, exacerbating antitrust concerns over market foreclosure and reduced innovation incentives. Federal regulators, enforcing the new act, required UATC to divest within five and a half months, leading the company to propose a three-way split in July 1934: one unit for transport (United Air Lines), one for airplane manufacturing (Boeing Airplane Company), and one for engines and accessories (, incorporating and Sikorsky). The dissolution was finalized on September 26, 1934, marking a pivotal antitrust intervention that dismantled UATC's empire and reshaped the aviation industry by separating manufacturing from operations, though critics like William Boeing argued it hindered efficiency without addressing underlying competitive dynamics. This breakup preserved Boeing's division but curtailed its influence over fleets, indirectly opening opportunities for rival manufacturers like Douglas to supply competitors with comparable twin-engine airliners.

Impact of Airmail Scandal and Legislation

The emerged from a 1933 congressional investigation into the awarding of lucrative airmail contracts under the Air Mail Act of 1930, revealing collusion among major airlines and their parent holding companies, including (UATC), which controlled Boeing Airplane Company and United Air Lines. UATC had leveraged airmail subsidies to fund the rapid development of the Boeing 247, an advanced twin-engine airliner introduced in 1933 exclusively for United Air Lines, enabling the carrier to dominate transcontinental routes with superior speed and capacity. On February 9, 1934, President canceled all private airmail contracts via executive order, citing monopolistic practices, and reassigned delivery to the U.S. Army Air Corps, which proved disastrous with adverse winter weather, inadequate equipment, and 12 fatalities among the 66 involved pilots. This abrupt disruption slashed United Air Lines' revenue—airmail had accounted for up to 80% of its income—hampering expansion of its Boeing 247 fleet and forcing reliance on less profitable passenger services amid the . The ensuing Air Mail Act of 1934, enacted on June 12, prohibited aircraft manufacturers from holding more than 5% equity in airlines, directly targeting vertically integrated entities like UATC to curb perceived monopolies and promote competition. In response, UATC dissolved in September 1934, spinning off United Air Lines as an independent operator on September 26 and reorienting Boeing Airplane Company toward pure manufacturing, severing the financial and operational synergies that had accelerated the 247's engineering innovations, such as its all-metal semimonocoque fuselage and retractable . The also mandated competitive bidding for reissued contracts at reduced rates—capping compensation at 35 cents per pound for the first 1,000 miles, down from prior highs—and allocated routes to smaller carriers, diluting the of majors like United and limiting their ability to subsidize advanced operations like the 247 through mail revenues. These reforms shifted industry emphasis from mail-dependent models to passenger transport, indirectly benefiting the Boeing 247's role in pioneering all-weather, high-speed commercial flights but constraining United's fleet growth to just 60 units due to capital shortages post-cancellation. Boeing founder William Boeing, disillusioned by the government's intervention, resigned from UATC in October 1934 and sold his interests, exiting entirely and contributing to the company's pivot away from aggressive airline integration that had birthed the 247. The scandal and legislation thus dismantled the ecosystem that prioritized the 247's deployment, fostering a more fragmented market where competitors like Douglas could challenge with designs such as the DC-2 and DC-3, ultimately eroding the 247's early competitive edge.

Operational Deployment

Entry into Commercial Service

The Boeing 247 entered commercial service with United Air Lines in 1933 as the first all-metal twin-engine passenger airliner, featuring low-wing design and retractable landing gear. United Air Lines, formerly Boeing Air Transport, received the initial deliveries and began operations on transcontinental routes, enabling faster coast-to-coast travel without overnight stops. This deployment revolutionized air transportation by accommodating 10 passengers at speeds up to 200 mph, outpacing biplane competitors like the Ford Trimotor. By the latter half of 1933, United operated a fleet of 59 247s, conducting regular flights carrying passengers, mail, parcel post, and air express. Key routes included segments from Newark to with stops in and Toledo, featuring hourly departures and amenities such as air hostess service, meals, and transfers. The aircraft's introduction spurred record ticket sales for United, reflecting public demand for its reliability and reduced flight times, such as 5¾ hours for the Newark-Chicago leg.

Military Adaptations and Wartime Use

During World War II, the Boeing 247 underwent limited military adaptations, primarily involving the conversion of existing civil airframes into transport and training configurations rather than purpose-built military variants. The United States Army Air Forces impressed 27 aircraft, redesignating them as C-73 transports. These conversions retained the core airframe with minimal structural changes, seating a crew of three plus up to 10 passengers or cargo, and most preserved the original Pratt & Whitney Wasp S1H1 engines, while others received military-grade R-1340-AN-1 powerplants. The C-73 maintained civil specifications, including a length of 51 feet 7 inches (15.72 meters) and a wingspan of 74 feet (22.58 meters), prioritizing rapid repurposing over extensive redesign. The C-73 fulfilled secondary utility roles such as logistics support and pilot training within the USAAF, but its wartime service proved short-lived due to the aircraft's age and the emergence of more capable designs like the Douglas C-47. No armament was added, reflecting its non-combat orientation, and operational use focused on domestic and limited overseas transport without significant frontline exposure. Canada's acquired eight ex-U.S. commercial 247s for transport duties, assigning them to No. 121 Squadron circa to ferry personnel and supplies. These aircraft supported early war efforts in before being struck off strength in 1942, with six transferred to Canadian Pacific Airlines by October 1, 1943, for continued civil-military hybrid operations. The United Kingdom's employed one Boeing 247, serial DZ203, as an experimental platform for , electronics testing, and blind-landing development, culminating in the first fully automatic blind landing on January 16, 1945. This adaptation underscored the 247's value in specialized technical evaluations amid wartime innovation demands. , some military-converted 247s persisted in service into the late 1960s, demonstrating enduring structural integrity despite limited numbers.

Variants and Configurations

Primary Variants

The Boeing 247 was initially produced as the Model 247, a twin-engine, low-wing monoplane with all-metal semi-monocoque construction, retractable landing gear, and Pratt & Whitney R-1340 Wasp radial engines rated at 550 horsepower each. This variant seated 10 passengers plus a crew of three (pilot, copilot, and steward), featured fixed-pitch propellers, and achieved a top speed of 182 mph with a cruise of 170 mph, enabling it to outperform tri-motor contemporaries like the Ford Trimotor. Only a limited number of early 247s were built before refinements, with initial deliveries to United Air Lines in 1933 emphasizing speed and reliability for short-haul routes. The primary production variant, the 247D, incorporated key enhancements including controllable-pitch propellers, wing de-icing boots using rubber expansion methods, and revised windshield raking for reduced glare on instruments. These modifications boosted top speed to 200 mph and cruise to approximately 190 mph, while improving high-altitude performance and all-weather capability; 53 units were delivered to United Air Lines, forming the bulk of the 75 total airframes produced. The 247D maintained the 10-passenger configuration but added operational efficiencies like for control surfaces, making it the definitive version for commercial service. A specialized sub-variant, the 247A, was tailored for Deutsche Luft Hansa with uprated 625 hp Pratt & Whitney Wasp engines for better hot-and-high performance, though production remained limited to export orders. Experimental models like the one-off 247D racer with tuned engines and streamlined features achieved record speeds but did not enter series production, highlighting Boeing's iterative approach to performance optimization. Overall, the 247 and 247D established benchmarks for twin-engine airliners, prioritizing structural integrity and engine redundancy over larger capacity.

Performance Modifications

The Boeing 247D variant represented the primary performance upgrade to the original Model 247, introduced to enhance speed and efficiency in response to competitive pressures from aircraft like the Douglas DC-2. Key modifications included the adoption of NACA low-drag engine cowlings, replacing the earlier or speed-ring cowlings, which reduced aerodynamic drag. Additionally, fixed-pitch propellers were substituted with controllable-pitch propellers, improving takeoff performance, climb rate, and single-engine handling by allowing optimal blade angles for different flight phases. These changes yielded measurable gains: the 247D achieved a top speed of and a cruise speed of approximately 189 mph at optimal altitude, compared to the original 247's cruise of around 165 mph. United Air Lines, the primary operator, retrofitted its existing fleet of 59 aircraft to the 247D configuration starting in 1934, applying the new cowlings and propellers to all but five original models. Engine power remained based on Wasp radial engines rated at 550 horsepower each, but the aerodynamic refinements effectively boosted overall efficiency without increasing fuel consumption proportionally. A specialized variant for in 1934 incorporated upgraded Wasp engines producing 625 horsepower each, further extending range and speed for transatlantic survey flights, though this was not a widespread modification. These enhancements solidified the 247's role as a benchmark for all-metal airliners, enabling nonstop coast-to-coast flights in the U.S. with reduced refueling stops, though they did not fully offset disadvantages in payload capacity relative to newer designs.

Operators and Fleet Utilization

Civil Operators

The Boeing 247 was initially operated exclusively by United Air Lines (formerly Boeing Air Transport), which took delivery of 60 aircraft starting in March 1933 for transcontinental routes in the United States. These twin-engine airliners, seating up to 10 passengers, enabled faster and more reliable service compared to prior transports, with United utilizing them for mail and passenger flights until the mid-1930s. Facing competition from the , which offered greater capacity, United began phasing out the 247 by early 1936, selling surplus aircraft to smaller regional carriers including Empire Air Lines, National Parks Airways, and Central Airlines. These operators employed the type for shorter domestic routes, often converting some for cargo or mixed use, with service continuing into the early before replacement by larger DC-3 airliners. Foreign civil operations were limited, with examples acquired second-hand or via special orders. Canadian Pacific Airlines operated at least one 247D for northern routes in the late . In , (successor to ) flew several 247Ds registered as C-142 through C-144 starting in 1937 for regional passenger and mail services. in received three , including modified 247As, primarily for evaluation and long-distance flights in the mid-1930s. Isolated instances occurred elsewhere, such as a single example with Viação Aérea Bahiana in and private ownership in and the . Overall, fewer than 10 served non-U.S. civil operators, reflecting the type's focus on American markets amid export restrictions and rapid obsolescence. ![United Airlines Boeing 247 NC13347][float-right]

Military Operators

The United States Army Air Forces impressed 27 Boeing 247D airliners into service as C-73 transports and trainers during World War II, primarily utilizing existing civilian aircraft rather than new production. These aircraft underwent modifications including re-powering with 600-horsepower Pratt & Whitney R-1340-AN1 radial engines in some cases to enhance performance for military roles such as multi-engine training and utility transport. Most C-73s were returned to civilian operators before the war's end, reflecting their interim wartime utility. The Royal Canadian Air Force acquired eight Boeing 247Ds, primarily ex-civilian examples, for service from 1940 to 1942 in roles including transport and training. Units operating these aircraft encompassed No. 1 Central Flying School at RCAF Station Trenton, Station Flight at RCAF Station Rockcliffe, and No. 121 Composite Squadron at RCAF Station Dartmouth, where they supported maritime operations and general utility tasks. Several featured distinctive markings, such as red tails and engine cowlings for instrument training identification. The Royal Air Force operated a single , serial DZ203, acquired in 1941 as a for advanced development, including airborne and blind systems. Originally a civilian , it was assembled in the UK upon arrival by sea and flown in RAF , contributing significantly to wartime until at least January 1945. One Boeing 247Y, an armed variant with military modifications, was exported to Chinese forces in for combat use against Japanese invaders, marking limited but direct application beyond roles. This sole example underscored the type's adaptability, though production remained minimal compared to standard civilian models.

Safety Record

Major Accidents and Incidents

The most notable incident involving the Boeing 247 occurred on October 10, 1933, when United Air Lines Trip 23, operating as NC13304, exploded in mid-air near , killing all three crew members and four passengers aboard. Investigation by the U.S. Department of Commerce and later authorities determined that a nitroglycerin-based , concealed in a , detonated in the baggage compartment, severing the tail section and causing the crash; this marked the first confirmed of a commercial airliner in U.S. history. No perpetrator was ever conclusively identified despite extensive inquiries. On February 23, 1934, Boeing Air Transport Flight 13, registered NC13357, crashed near , Utah, during approach in poor visibility, resulting in eight fatalities among the crew and passengers. The accident was attributed to and in instrument flight conditions, with the aircraft striking short of the . United Air Lines Flight 34, NC13317, suffered a fatal crash on October 7, 1935, near , claiming 12 lives after the aircraft encountered severe icing conditions en route from to Cheyenne, leading to loss of control and impact with mountainous . Meteorological factors, including unexpected supercooled water droplets causing rapid ice accumulation beyond the aircraft's de-icing capabilities, were cited as primary causes in the official report. Another significant event took place on December 27, 1936, when United Air Lines NC13355 crashed into terrain two miles southwest of Newhall, California, killing all 12 occupants due to pilot deviation from the assigned airway and failure to maintain proper altitude during night operations. The investigation highlighted navigational errors and possible fatigue as contributing factors. Later incidents included a July 30, 1942, crash of U.S. Army Air Forces Boeing 247D 42-68369 at Wold-Chamberlain Field, Minneapolis, Minnesota, which resulted in 10 fatalities; the cause was determined to be a pilot's improper response to an engine failure during takeoff. In civilian service, Líneas Aéreas Mexicanas XA-DUY crashed near Rio Verde, San Luis Potosí, Mexico, on August 1, 1945, with 12 fatalities attributed to controlled flight into terrain amid adverse weather. These events underscored early limitations in all-weather operations and de-icing technology for the type, though overall hull-loss rates improved with operational experience.

Comparative Safety Analysis

The Boeing 247's civil safety record included 22 fatal accidents resulting in 131 fatalities, according to data compiled by the Aviation Safety Network, a database aggregating verified incident reports from official investigations and aviation authorities. With only 75 aircraft produced between 1933 and 1940, primarily operated by United Air Lines on domestic routes, the type's limited fleet size constrained direct statistical comparisons but highlighted vulnerabilities typical of 1930s aviation, including susceptibility to icing, poor weather navigation without modern aids, and in instrument flight. One notable early incident on October 10, 1933, involved via a on United Air Lines Flight 20 near , killing all seven aboard and representing the first confirmed aerial bombing in U.S. commercial history, as determined by FBI and probes. Compared to pre-1930s airliners such as the or Boeing 40A, which relied on fabric-covered wings and open cockpits prone to structural fatigue and stall risks, the 247's all-metal construction, twin Wasp engines, and retractable enhanced redundancy and cruise stability, contributing to fewer in-flight breakups per operating hour. Industry-wide fatality rates in 1932 stood at 14.96 deaths per 100 million passenger-miles, driven by such outdated designs and lax regulations post the Air Mail scandal, which prompted federal oversight reforms that indirectly benefited the 247's operations. However, the type's compact 10-passenger capacity and shorter range (around 745 miles) exposed it to frequent refueling stops in adverse conditions, exacerbating icing-related crashes, as seen in multiple Wyoming incidents in 1935 where carburetor ice stalled engines without adequate anti-icing provisions. The , entering service in , surpassed the 247 in safety metrics through design refinements like greater for better lift, improved efficiency reducing vibration-induced failures, and optional de-icing boots, amid an industry shift that halved U.S. fatal accidents from eight in (for 63 million miles flown) to four in 1941 (for 133 million miles). While the DC-3 family logged thousands of hull losses over decades—reflecting over 16,000 units built and wartime use—their per-passenger-mile rate benefited from scaled operations and post-1934 training mandates, underscoring how the 247's pioneering features laid groundwork but were eclipsed by successors addressing capacity and environmental tolerances. Overall, the 247's record aligned with transitional benchmarks, where empirical advancements in materials and engines outpaced persistent human and meteorological factors until broader regulatory causal chains matured.

Technical Specifications

Boeing 247D Specifications

The Boeing 247D, the most numerous variant of the Boeing 247 airliner, incorporated geared Wasp engines for enhanced performance over earlier models. It featured an all-metal fuselage, low-mounted wings with split flaps, and retractable main , with a fixed tailwheel. General characteristics
  • Crew: 3 (pilot, copilot, flight attendant)
  • Capacity: 10 passengers in five rows of paired seats separated by an aisle
  • Length: 51 ft 7 in (15.7 m)
  • Wingspan: 74 ft (22.6 m)
  • Height: 12 ft 6 in (3.8 m)
  • Wing area: 836 sq ft (77.7 m²)
  • Empty weight: 8,940 lb (4,055 kg)
  • Max takeoff weight: 13,650 lb (6,192 kg)
  • Powerplant: 2 × Pratt & Whitney R-1340-S1H1-G Wasp 9-cylinder air-cooled radial piston engines, 550 hp (410 kW) each
Performance
  • Maximum speed: 200 mph (322 km/h) at
  • Cruise speed: 189 mph (304 km/h)
  • Range: 745 mi (1,199 km) normal, with reserves
  • Service ceiling: 25,400 ft (7,740 m)
  • Rate of climb: 1,150 ft/min (5.8 m/s)

Legacy and Preservation

Influence on Aviation Standards and Competition

The Boeing 247 established key aviation standards through its pioneering all-metal construction, twin Wasp engines mounted on the wings for better , and retractable , which reduced drag and improved cruise speeds to 200 mph—approximately 50 percent faster than prevailing trimotor airliners like the . The 247D variant further advanced norms with controllable-pitch propellers for optimized thrust across flight phases and pneumatic wing de-icer boots, enhancing all-weather reliability and setting precedents for passenger safety in icing conditions. These features, combined with innovations like for control surface adjustment and an early system, shifted industry design toward efficient, low-drag monoplanes, influencing subsequent models in streamlining production and operational economics. Boeing's initial refusal to sell the 247 to non-United Airlines operators—producing the first 60 units exclusively for its affiliate—created a monopoly for United, limiting total production to 75 aircraft and stifling broader market adoption. This exclusivity, rooted in the of (which encompassed and ), drew federal antitrust scrutiny amid the 1934 Air Mail Act reforms, culminating in the compelled breakup of the into separate manufacturing (), airline (United), and transport entities to foster competition. The 247's dominance prompted rivals like Transcontinental & Western Air (TWA) to solicit alternatives, directly commissioning Douglas Aircraft's DC-1 prototype in 1933 as a faster, more spacious competitor capable of 210 mph cruises and 12-14 passengers. This rivalry accelerated the DC-2's development, which won the 1934 Collier Trophy partly in response to the 247, and paved the way for the DC-3's mass-market success with lower operating costs and greater capacity. By rendering tri-motor designs obsolete and forcing iterative improvements in speed, payload, and reliability, the 247 catalyzed a competitive surge that lowered fares and expanded commercial viability, though its own commercial limitations underscored the risks of proprietary control over breakthrough technology.

Surviving Aircraft and Restoration Efforts

Four Boeing 247D aircraft survive, all preserved in museum collections as static displays following the type's retirement from service decades earlier. These examples represent the pioneering all-metal, twin-engine airliner introduced in 1933, with constructors' numbers (c/n) spanning early production. The most extensively restored survivor is c/n 1729 (NC13347, named City of Renton), originally delivered to United Air Lines in 1934. Acquired by the Museum of Flight in Seattle in 1966, it underwent a 15-year restoration beginning in 1976 at Paine Field, involving volunteers including retired United Airlines personnel who contributed authentic components and markings from Pacific Air Transport operations. The aircraft achieved airworthiness and performed its final flight on April 26, 2016, a short hop from Paine Field to Boeing Field for permanent exhibit in the Museum's Aviation Pavilion, marking the last powered flight of any Boeing 247. Another key example is the first production 247D (c/n 1698, NC1934), displayed at the National Air and Space Museum in Washington, D.C. This aircraft, which incorporated upgrades like controllable-pitch propellers and de-icer boots, entered service with United Air Lines in 1934 and was later acquired for preservation to highlight early advancements in commercial aviation design. The in holds c/n 1699 (CF-BVZ), a former Western Air Express and Canadian Pacific Airlines aircraft transferred to museum custody in the 1960s after military evaluation by the Royal Canadian Air Force during . In the United Kingdom, c/n 1722 (N18E, formerly NC13340 with United Air Lines and Island Airlines) resides in storage at the Science Museum's National Collections Centre at Wroughton, having been ferried across the Atlantic in 1982 for preservation without major restoration documented beyond basic stabilization. No active restoration projects continue on these airframes, as their historical value prioritizes static conservation over flight operations due to age, parts scarcity, and structural fatigue risks.

Long-Term Economic and Technological Impact

The Boeing 247 introduced foundational technological advancements that shaped design for decades, including an all-metal , low-wing configuration, and retractable , enabling cruise speeds of approximately 200 miles per hour for 10 passengers over ranges up to 1,600 miles. These features converged prior breakthroughs in and materials, proving the viability of efficient, streamlined transports that prioritized speed and structural integrity over the drag-prone biplanes of the era. Subsequent variants like the 247D incorporated controllable-pitch propellers and pneumatic wing de-icers, enhancing all-weather reliability and directly influencing competitors' aircraft, such as the , which adapted similar and metal-construction principles to achieve comparable performance gains. The aircraft's innovations accelerated the transition to modern airframe standards, establishing templates for load-bearing skins, enclosed cabins with reduced noise via insulation, and improved ventilation for passenger comfort, which became ubiquitous in post-1930s airliners. By demonstrating scalable twin-engine power for multi-role operations—including early military adaptations—the 247 contributed to the evolution toward larger, more efficient designs, though its unpressurized cabin and limited capacity highlighted needs addressed in later models like the DC-3. Economically, the 247 boosted operational efficiency for early adopters like , enabling non-stop transcontinental flights and higher reliability that cut effective travel costs per passenger-mile compared to predecessors like the , which cruised at half the speed. However, with only 75 units produced—stemming from Boeing's exclusive supply deal with United that deterred rivals—its market dominance was curtailed, sparking intense that drove industry-wide innovations and cost reductions. This rivalry, exemplified by TWA's commissioning of the DC-2 and DC-3, expanded capacity to 21 passengers at lower fares, broadening air travel's accessibility and fueling long-term growth in passenger revenues exceeding subsidies by 1936. In the broader economy, the 247's exclusivity prompted U.S. regulatory reforms via the 1934 Air Mail Act, which dismantled airline-manufacturer and promoted competitive , indirectly lowering and scaling aviation's contribution to national transport infrastructure. Its technological precedents endured, informing the high-volume production of versatile airframes that underpinned aviation's post-World War II expansion, though the 247 itself yielded limited direct manufacturing scale due to its premium positioning.

References

  1. https://airandspace.si.edu/collection-objects/boeing-247-d/nasm_A19540069000
  2. https://www.museumofflight.org/exhibits-and-events/aircraft/boeing-247d
  3. https://www.robertnovell.com/bloggolden-years-and-technology-part-one-boeing-247-airliner-june-052009-2/
  4. https://www.historylink.org/File/22859
  5. https://simpleflying.com/why-boeings-own-airline-stopped/
  6. https://sandiegoairandspace.org/exhibits/online-exhibit-page/the-airmail-scandal
  7. https://www.skytamer.com/Boeing_247D.html
  8. https://www.boeing.com/content/dam/boeing/boeingdotcom/history/pdf/Boeing-Chronology.pdf
  9. https://shop.historynet.com/blogs/new-the-latest-from-historynet-com/was-the-boeing-247-really-everything-it-s-supposed-to-be
  10. https://aeropedia.com.au/content/boeing-247/
  11. https://simpleflying.com/boeing-247-first-flight-anniversary/
  12. https://www.smithsonianmag.com/air-space-magazine/in-the-museum-the-original-airliner-1601/
  13. https://www.historynet.com/boeing-247-failures/
  14. https://www.centennialofflight.net/essay/Aerospace/Boeing%27s_Metal_Planes/Aero18.htm
  15. https://www.militaryfactory.com/aircraft/detail.php?aircraft_id=2295
  16. https://secure.boeingimages.com/archive/Boeing-Model-247-Airline-Service--1930s-2JRSXLJBGUCX.html
  17. https://aerotechnews.com/blog/2016/05/09/boeing-innovations-sometimes-lucrative-sometimes-a-bust/
  18. https://simpleflying.com/why-was-douglas-dc-3-so-important/
  19. https://www.historylink.org/File/3546
  20. https://www.historylink.org/file/5368
  21. https://americanbusinesshistory.org/united-the-little-known-history-behind-another-giant-merger/
  22. https://www.nytimes.com/1934/07/28/archives/united-aircraft-asks-3unit-split-two-manufacturing-and-one.html
  23. https://airandspace.si.edu/stories/editorial/air-mail-crisis
  24. https://www.historylink.org/File/9300
  25. https://commons.erau.edu/cgi/viewcontent.cgi?article=1207&context=space-congress-proceedings
  26. https://www.ukessays.com/essays/social-policy/airmail-act-of-1934-effects-on-the-airline-industry.php
  27. https://www.faa.gov/sites/faa.gov/files/about/history/milestones/Airmail_Comes_of_Age.pdf
  28. https://blog.euroavia.eu/2024/09/03/the-air-mail-scandal-a-tale-of-corruption-and-reform/
  29. https://www.centennialofflight.net/essay/Commercial_Aviation/UnitedAirlines/Tran16.htm
  30. https://airandspace.si.edu/stories/editorial/take-trip-boeing-247
  31. https://www.historyofwar.org/articles/weapons_boeing_C-73.html
  32. https://www.daveswarbirds.com/usplanes/aircraft/c-73.htm
  33. https://simpleflying.com/boeing-247-story-and-cost/
  34. https://caspir.warplane.com/aircraft/serial-search/aircraft-no/200000029
  35. https://www.silverhawkauthor.com/post/canadian-warplanes-4-boeing-247d
  36. http://www.boeing.com/content/dam/boeing/boeingdotcom/history/pdf/Boeing_Products.pdf
  37. https://generalaviationnews.com/2020/03/29/boeing-247-set-the-tone-for-airliners/
  38. http://www.skytamer.com/Boeing_247D.html
  39. https://www.aircraftinvestigation.info/airplanes/Boeing_247D.html
  40. https://www.boeing.com/content/dam/boeing/boeingdotcom/history/pdf/Boeing_Products.pdf
  41. http://www.airhistory.org.uk/gy/reg_C-.html
  42. https://www.worldwarphotos.info/gallery/usa/aircrafts-2-3/c-73/
  43. https://1000aircraftphotos.com/Contributions/CrupiRay/12055.htm
  44. https://deffordairfieldheritagegroup.wordpress.com/aircraft-at-defford/boeing-247d-dz203/
  45. https://www.historynet.com/what-happened-to-ual-flight-23/
  46. https://www.guinnessworldrecords.com/world-records/first-aircraft-sabotage
  47. https://www.thisdayinaviation.com/10-october-1933/
  48. https://asn.flightsafety.org/asndb/type/b247
  49. https://vault.fbi.gov/1993-crash-of-united-airlines-trip-23-boeing-247-nc13304
  50. http://www.flugzeuginfo.net/acdata_php/acdata_boeing_247_en.php
  51. https://www.theaviationvault.com/early-accident-rates
  52. https://www.baaa-acro.com/aircraft/boeing-247
  53. http://www.dc3history.org/douglasdc3.html
  54. https://asn.flightsafety.org/database/types/Douglas-DC-3/index
  55. http://www.aviation-history.com/boeing/247.html
  56. https://ingenium.ca/aviation/en/collection-highlight/boeing-247d/
  57. https://simpleflying.com/boeing-247-aviation-future-influence-analysis/
  58. https://airandspace.si.edu/stories/editorial/making-modern-airliner
  59. https://www.robertnovell.com/how-boeing-made-the-douglas-dc-3-a-success-november-17-2017-2/
  60. https://vintageaviationnews.com/aviation-museum-news/boeing-247-flight.html
  61. https://www.historylink.org/File/22868
  62. https://vintageaviationnews.com/warbirds-news/randys-warbird-profiles-boeing-model-247d-s-n-1729-nc13347.html
  63. https://www.airhistory.net/photo/351256/N18E
  64. https://library.fiveable.me/key-terms/hs-washington-state-history/boeing-247
  65. https://airandspace.si.edu/stories/editorial/big-three
  66. https://www.ebsco.com/research-starters/history/dc-3-opens-new-era-air-travel
  67. https://airandspace.si.edu/explore/stories/early-commercial-aviation
Add your contribution
Related Hubs
User Avatar
No comments yet.