The Boeing Model 307 Stratoliner was the world's first high-altitude commercial transport and the first four-engine airliner in scheduled domestic service. The Stratoliner was the first airplane to have a flight engineer as a member of the crew. The engineer was responsible for maintaining power settings, pressurization and other subsystems, leaving the pilot free to concentrate on other aspects of flying the aircraft. The Boeing Model 307 circular fuselage provided maximum space for the five crew members and 33 passengers. The nearly 12-foot-wide cabin had space for comfortable berths for overnight travelers.