Boeing 307

The Boeing Model 307 Stratoliner was the first commercial transport aircraft to enter service with a pressurized cabin. This feature allowed the aircraft 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 altitude was 8,000 ft. The Model 307 had capacity for a crew of five 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.