The Federal Aviation Act was passed by Congress. D was given the authority, to promote safety of flight of civil aircraft in air commerce by prescribing and revising from time to time reasonable rules and regulations governing, in the interest of safety, the maximum hours or periods of service of airmen, and other employees, of air carriers; and reasonable rules and regulations, or minimum standards, governing other practices, methods, and procedure, as D may find necessary to provide adequately for national security and safety in air commerce. D and his medical staff began a study concerning the aging process and the diseases and physiological deterioration that accompany it in an effort to determine whether a maximum age should be set for service by commercial pilots. D published a proposed regulation in substance the same as that ultimately prescribed. In accordance with the rule-making requirements of §4 of the Administrative Procedure Act, opportunity was afforded for the submission of written data and briefs. About one hundred comments were received. A large majority favored the regulation. No hearing was held since D determined, as he was entitled to under the rulemaking provisions of the Administrative Procedure Act, that a hearing would not 'serve a useful purpose' and that it was not 'necessary in the public interest.' On December 1, 1959, D promulgated a regulation which provides: 'No individual who has reached his 60th birthday shall be utilized or serve as a pilot on any aircraft while engaged in air carrier operations.' P brought suit in January 1960 for a declaratory judgment that the regulation was null and void and for an injunction against its threatened application. Ps contend that the regulation is invalid because it was issued without the holding of adjudicatory hearings required by the Administrative Procedure Act, 5 U.S.C.A. §§ 1001-1011, and by §609 of the Federal Aviation Act of 1958, 49 U.S.C.A. § 1429, before an airman's license may be amended, modified, suspended or revoked, and because it was arbitrary, discriminatory and without reasonable relation to the standards set forth in § 601 of the Act, 49 U.S.C.A. § 1421, under which it was issued. Ps also claim that the regulation deprives them of property without due process of law. The district court denied Ps' motion for a preliminary injunction but reserved judgment on D's cross-motion for summary judgment. P appealed.