Northwest Airways Timetable 1931 April 1
MLA
Northwest Airlines. "Northwest Airways Timetable 1931 April 1." Delta Flight Museum. 1931-04-01, https://dlg.galileo.usg.edu/do:delta_nwa-tt_nwa-tt-19310401.
APA
Northwest Airlines (1931-04-01). Northwest Airways Timetable 1931 April 1. Retrieved from https://dlg.galileo.usg.edu/do:delta_nwa-tt_nwa-tt-19310401
Chicago
Northwest Airlines. "Northwest Airways Timetable 1931 April 1." 1931-04-01. June 20, 2025. https://dlg.galileo.usg.edu/do:delta_nwa-tt_nwa-tt-19310401.
