14 CFR 121.538 : Aeronautics And Space (§ 1.1 To Parts 1311-1399) — (§ 110.1 To Part 199) — Federal Aviation Administration, Department Of Transportation (Continued) (§ 110.1 To Part 199) — Air Carriers And Operators For Compensation Or Hire: Certification And Operations (§ 110.1 To § 139.343) — Operating Requirements: Domestic, Flag, And Supplemental Operations (§ 121.1 To Appendix P To Part 121) — Flight Operations (§ 121.531 To § 121.590) — Aircraft security.