251. Federal aviation regulations; Part 123, Certification and operations, air travel clubs using large airplanes. Bookmark SuDoc number: TD 4.6:123
252. Federal aviation regulations; Part 127, Certification and operations of scheduled air carriers with helicopters. Bookmark SuDoc number: TD 4.6:127
253. Federal aviation regulations; Part 133, Rotocraft external load operations. Bookmark SuDoc number: TD 4.6:133
254. Federal aviation regulations; Part 135, Air taxi operators and commercial operations of small aircraft. Bookmark SuDoc number: TD 4.6:135
255. Federal aviation regulations; Part 139, Certification and operations: Land airports serving CAB certificated air carriers. Bookmark SuDoc number: TD 4.6:139
258. Federal aviation regulations; Part 21, Certification procedures for products and parts. Bookmark SuDoc number: TD 4.6:21
259. Federal aviation regulations; Part 23, Airworthiness standards, normal, utility, and acrobatic category airplanes. Bookmark SuDoc number: TD 4.6:23
260. Federal aviation regulations; Part 25, Airworthiness standards, transport category airplanes. Bookmark SuDoc number: TD 4.6:25