Boeing Model 221 Monomail

Generally similar to the Model 200 Monomail, this single aircraft had a fuselage lengthened by 0.2m and cargo/mail capacity reduced from 1043kg to 340kg, to provide accommodation for six passengers in an enclosed cabin; first flown on August 1930, and entered service with Boeing Air Transport

Boeing Model 221A: designation applied to the Models 200 and 221 following fuselage 'stretches' to provide accommodation for eight passengers; both saw service on the Cheyenne-Chicago route of Boeing's newly-formed United Air Lines