There is some non "planes related" pictures, and some seem not to be tagged as "public domain". But most of the planes pictures were made by the Air Force and thus should be in the public domain. Some examples of the pictures of the album:
Today in 1936 - Boeing YB-17 Maiden Flight // Convair YB-60 Jet
Bell X-15 Rocket Plane and Boeing B-52 Flyover // HL-10 Lifting Body and B-52 Flyover
Boeing B-29 // Today in 1974 - B-1 Bomber First Rollout