The Bleriot-SPAD S.33 was a small French airliner developed soon after World War I. A great success, the S.33 dominated its field throughout the 1920s, initially on CMA's Paris-London route, and later on continental routes serviced by Franco-Roumaine. The aircraft was a biplane of conventional configuration whose design owed much to the Blériot company's then-recent fighter designs such as the S.20. Four passengers could be accommodated in an enclosed cabin within the monocoquefuselage, and a fifth passenger could ride in the open cockpit beside the pilot.
One interesting development was a sole example converted by CIDNA to act as a blind-flying trainer. A set of controls was installed inside the passenger cabin, the windows of which had been blacked out.
"The Spad "Berline" S.33 bis" (PDF). FlightXIII (27): 460–462. 7 July 1921. No. 654. Retrieved 26 April 2012. Contemporary technical description of the Blériot-SPAD S.33, including photographs and drawings.