Development HistoryAlthough Boeing had suffered a setback because of Douglas's unprecedented success with the DC-2 and DC-3 family of true airliners, it did not take long to rebound. Even as the DC-3 was starting a new era, by introducing unit operating costs low enough for an airline to make a profit, the Boeing 307 was developed to start another era, that of pressurized comfort at higher altitudes than had hitherto been contemplated.
The aircraft was the result of considerable research in high altitude flying by "Tommy" Tomlinson, of T.W.A., who was estimated to have flown more hours above 30,000 feet than all other pilots combined. Resulting from his recommendations, Boeing produced an airliner which could cruise at 14,000 feet, or, as the neatly descriptive phrase went at the time, "above the weather." The Model 307, or Stratoliner, was a straightforward conversion from the supremely successful B-17 Flying Fortress bomber, with a 33-seat commercial fuselage substituted for the bomber's. The most important technical feature was that the entire cabin was pressurized so that the use of special oxygen equipment was unnecessary. Pressure differential was 2 1/2 lb/sq. in. Another aspect of the stringent specifications was that high octane fuel was being developed to obtain higher supercharger pressure to maintain engine power at high altitudes.