APA

United States, . (1972). Private and commercial pilots refresher courses, 1972. [Washington, D.C: .

Chicago

United States, . 1972. Private and commercial pilots refresher courses, 1972. [Washington, D.C: .

Harvard

United States, . (1972). Private and commercial pilots refresher courses, 1972. [Washington, D.C: .

MLA

United States, . Private and commercial pilots refresher courses, 1972. [Washington, D.C: . 1972.