page_title: Boeing 307 Stratoliner
section_title: Operational history
hierarchical_section_title: Boeing 307 Stratoliner / Operational history
caption_attribution_description: English: Boeing 307 at Paya Lebar, Singapore in 1967.
context_page_description: The Boeing Model 307 Stratoliner was an American commercial transport aircraft that entered commercial service in July 1940. It was the first to offer a pressurized cabin, allowing it to cruise at an altitude of 20,000 ft, well above many weather disturbances. The pressure differential was 2.5 psi, so at 14,700 ft the cabin air pressure was equivalent to an altitude of 8,000 ft. The Model 307 had capacity for a crew of six and 33 passengers. The cabin was nearly 12 ft across. It was the first land-based aircraft to include a flight engineer as a crew member. In addition to its civilian service it was also flown as the Boeing C-75 Stratoliner by the United States Army Air Forces, who used it as a long-range cargolift aircraft.
context_section_description: The maiden flight of the first Boeing 307 Stratoliner (not a prototype, as it was planned to be delivered to Pan Am following testing and certification), registration NX 19901 took place from Boeing Field, Seattle on December 31, 1938.
  This aircraft crashed on March 18, 1939, while being demonstrated to representatives of KLM. After takeoff the aircraft climbed to an altitude of 11,000 feet. At this altitude, longitudinal stability tests were made. The next tests, as outlined by the flight plan, were side-slip tests. The aircraft went into an inadvertent spin subsequent to a stall at an altitude of approximately 11,000 feet. It made two to three turns in the spin, during which the engines were used to aid recovery. In recovering from the dive subsequent to the spin, the wings and horizontal tail surfaces failed upward apparently due to air loads in excess of those for which the aircraft was designed. The ten people aboard, including the KLM technical director, a representative of the Dutch Air Ministry, a Boeing test pilot, the Boeing Chief Aerodynamicist, the Boeing Chief Engineer, and a TWA representative were killed.
  Subsequent wind tunnel testing showed that the addition of an extended dorsal fin ahead of and attached to the vertical tail prevented rudder lock. This was incorporated into the 307's rudder redesign, while also being incorporated in Boeing's rear fuselage redesign for their models "E" through "G" B-17 bomber.
  The first delivery to a customer was to multi-millionaire Howard Hughes, who bought one 307 (NX-19904) for a round-the-world flight, hoping to break his own record of 91 hours 14 minutes set from July 10–14, 1938 in a Lockheed 14. Hughes' Boeing Stratoliner was fitted with extra fuel tanks and was ready to set out on the first leg of the round-the-world attempt when Nazi Germany invaded Poland on September 1, 1939, causing the attempt to be abandoned. This 307 later had the extra fuel tanks removed, was fitted with much more powerful Wright R-2600 engines, and was transformed into the luxurious "The Flying Penthouse" for Hughes, although it was little used, eventually being sold to oil tycoon Glenn McCarthy in 1949.
  Deliveries to Pan Am started in March 1940, with TWA receiving its first 307 in April. TWA's Stratoliners flew three-stop flights between Los Angeles and New York while Pan Am's flew from Miami to Latin America. Ten 307s were built, three being delivered to Pan-Am (NC-19902:Clipper Rainbow, NC-19903:Clipper Flying Cloud, and NC-19910:Clipper Comet) and five to TWA (NC-19905:Comanche, NC-19906:Cherokee, NC-19907:Zuni, NC-19908:Apache, and NC-19909:Navajo) with one aircraft going to Hughes (NX-19904).
  On the entry of the United States into World War II, Pan Am (PAA) continued operating its Stratoliners on routes to Central and South America, but under direction of the Army Air Forces' Air Transport Command, while the TWA 307s were sold to the United States government, being designated Boeing C-75 (42-88623/27) and operated by the United States Army Air Forces (although normally still flown by TWA crews).
  The Army returned its five C-75s to TWA in 1944, which sent them back to Boeing for rebuilding. Boeing replaced the wings and horizontal tail with those from the B-17G, while more powerful engines were fitted and the electrical system was replaced with one based on the B-29 Superfortress. Passenger capacity was increased from 33 to 38. The total rebuilding cost to TWA was $2 million; the five aircraft re-entered passenger service on April 1, 1945. Although TWA was committed to the larger and faster Lockheed Constellation, it kept the Stratoliners until April 1951.
  Pan Am flew its unmodified 33-passenger Stratoliners between Miami and Havana until 1947, then sold them to small operators, including Aerovias Ecuatorianas AREA). Some later returned to the US, whilst others went to South-East Asia to replace write-offs. One aircraft (N-19903) was purchased by the Haitian Air Force, being fitted as a Presidential transport for François "Papa Doc" Duvalier. This aircraft later returned to the U.
caption: An Aigle Azur Stratoliner at Paya Lebar in 1967
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