Boeing Type 40B-4 "Mailplane"
United States — single-engined mail and passenger-carrying biplane

Archive Photos

1927 Boeing 40B-4 (NC285) at the Henry Ford Museum, Dearborn, MI


  • Boeing Model 40
  • Role: Mail plane
  • Manufacturer: Boeing
  • First flight: 20 July 1925
  • Introduced: 1 July 1927
  • Number built: ca. 80

The Boeing Model 40 was a United States mail plane that became the first aircraft built by the Boeing company to carry passengers. It was of conventional biplane configuration with a combination of standard and warren-truss style interplane struts. Originally designed to compete for a US Mail contract in 1925, it was rejected in favour of the Douglas M-2.

The design was revived in 1927 as part of Boeing's tender for newly privatised airmail routes. Designated the Model 40A, this variant was powered by an air-cooled Pratt & Whitney Wasp radial engine, which offered a 200 lb weight saving over the water-cooled Liberty specified by the postal service in 1925. Although the primary purpose of the aircraft was to carry mail, two passengers could be accommodated in the small cabin, allowing Boeing to operate it on any of the routes that the firm might bid for. The original fuselage design was changed to one using welded steel tubing. Boeing successfully bid on the San Francisco-Chicago route, and Boeing Air Transport commenced operations on 1 July 1927 with 24 Model 40As.


  • As of February 17, 2008, Boeing 40C S/N 1043 became the only airworthy example in the world. It also holds the title of the oldest flying Boeing in the world. In 1928, the aircraft was substantially damaged in a crash and was totally rebuilt over a seven year period and an estimated 18,000 man hours by Pemberton and Sons Aviation in Spokane, Washington.
  • The Henry Ford Museum in Dearborn, Michigan, contains a 1927 Boeing 40B-2, number 285.
  • The Museum of Science and Industry in Chicago, Illinois has a 1928 Boeing Model 40-B on display in its Transportation Gallery. (N288)
  • The Museum of Flight in Seattle, Washington has a complete full-scale replica and two partially finished replica fuselages (showing what the original Boeing factory would have looked like circa 1928-29) on display.


  • Model 40: Original 1925 design with Liberty engine.
  • Model 40A: Revised 1927 design for BATC. the aircraft was powered by a Pratt & Whitney Wasp radial engine, plus seating for two passengers in an enclosed cabin; 25 built.
  • Model 40B: Model 40As re-engined with a 525-hp (391-kW) Pratt & Whitney Hornet radial piston engine. 19 Model 40A were converted. Redesignated Model 40B-2.
  • Model 40B-4: Revised Model 40B with seating for four passengers and other improvements. Equipped with openable windows, plus seating for four passengers; 38 built.
  • Model 40B-4A: One Model 40B used as engine testbed by Pratt & Whitney.
  • Model 40H-4: Four Model 40B-4s built by Boeing Canada. Two aircraft were exported on New Zealand.
  • Model 40C: Similar to Model 40B-4 but with Pratt & Whitney Wasp engine of Model 40A. (10 built, all later converted to Model 40B-4 standard).
  • Model 40X: Unique special-order machine similar to Model 40C with only two-passenger cabin and extra open cockpit forward of pilot's cockpit.
  • Model 40Y: Unique special-order machine similar to Model 40X, but with Pratt & Whitney Hornet engine.


  • United States: Boeing Air Transport

Specifications (Model 40B-4)

General Characteristics

  • Crew: 1
  • Capacity: 2 passengers
  • Length: 33 ft 3 in
  • Wingspan: 44 ft 2 in
  • Height: 12 ft 3 in
  • Wing area: 545 ft²
  • Gross weight: 6,075 lb
  • Powerplant: 1 × Pratt & Whitney Hornet, 525-hp


  • Cruise speed: 125 mph
  • Range: 535 miles
  • Service ceiling: 16,100 ft


  1. Photos: John Shupek, Copyright © 2009 Skytamer Images. All Rights Reserved
  2. Wikepedia. Boeing Model 40, 4 December 2009
  3. Redding, Robert and Yenne, Bill. “Boeing Planemaker to the World”, Thunder Bay Press, San Diego, 1997, ISBN 1-57145-045-9, pp. 37

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