Federal Aviation Regulations: How Title 14 Is Organized

Title 14 and Its Parts

The federal aviation regulations are Title 14 of the Code of Federal Regulations, titled Aeronautics and Space. The Code is the codification of the general and permanent rules that federal agencies publish in the Federal Register, and the FAA’s rules are in Chapter I of Title 14. The rules are also called the Federal Aviation Regulations, a name that appears in the text of 14 CFR 91.23.

Chapter I is divided into subchapters, and each subchapter into numbered parts that each cover one subject. Aircraft design, certification, and maintenance rules are in Subchapter C, which runs from Part 21 through Part 49. Pilot certification is in Subchapter D, general operating rules are in Subchapter F, and rules for air carriers and operators for compensation or hire are in Subchapter G. Part 5, on safety management systems, is in Subchapter A, and Part 145, on repair stations, is in Subchapter H.

The table lists the parts that matter most for aviation safety, who each one governs, and what each one covers.

Part 91, Part 121, and Part 135

Part 91 is the baseline. It prescribes the rules governing the operation of aircraft within the United States. An air carrier or commercial operator that carries people or cargo for compensation or hire generally must also hold a certificate under Part 119 and follow Part 121 or Part 135, subject to the exclusions in 14 CFR 119.1. Those parts add requirements on top of the rest of the chapter; persons subject to Part 119 must still comply with the other requirements except where Parts 119, 121, 125, or 135 modify them or add to them.

Which of the two parts applies depends on the aircraft and the service. 14 CFR 110.2 defines the kinds of operations, and 14 CFR 119.21 assigns each kind to a part.

• Domestic and flag operations are scheduled operations with airplanes that are turbojet-powered, have more than 9 passenger seats, or have a payload capacity above 7,500 pounds. Part 121 governs them.
• Supplemental operations are common carriage operations with larger airplanes, and they include charter flights negotiated with a customer and all-cargo operations. Part 121 governs them.
• Commuter operations are scheduled operations with at least five round trips per week on at least one route, flown with rotorcraft or with non-turbojet airplanes of 9 passenger seats or fewer and a payload capacity of 7,500 pounds or less. Part 135 governs them.
• On-demand operations include flights whose departure time and locations are negotiated with the customer, flown with airplanes of 30 seats or fewer and a payload capacity of 7,500 pounds or less, or with any rotorcraft, and small all-cargo operations. Part 135 governs them.

The dividing lines are aircraft size, schedule, and type of service, not the quality of the operator. The parts also differ in timing and detail. The safety management system rule, for example, gave Part 121 certificate holders with an existing system until May 28, 2025 to revise it, while Part 135 certificate holders have until May 28, 2027 to implement one. Both parts place operational control on the certificate holder, a point covered in the discussion of who is responsible for aviation safety.

How a Rule Is Made

The FAA adopts, amends, and repeals regulations using Administrative Procedure Act procedures, which 14 CFR Part 11 implements. Under that statute, 5 U.S.C. 553, an agency publishes a notice of proposed rulemaking in the Federal Register stating its legal authority and the terms or substance of the proposal, gives interested persons an opportunity to comment, and includes a concise statement of the rule’s basis and purpose when it adopts the rule.

A notice of proposed rulemaking proposes specific regulatory changes for public comment and includes proposed regulatory text. A final rule sets out the new or revised requirements and their effective date, and when a notice of proposed rulemaking came first it also identifies significant issues raised by commenters and gives the agency’s response. A substantive rule generally must be published at least 30 days before it takes effect, with exceptions.

The effective date and the date an operator must comply can differ. The safety management systems final rule appeared in the Federal Register on April 26, 2024 (89 FR 33068), took effect May 28, 2024, and set compliance deadlines that run to May 28, 2027 for some operators.

The FAA does not always propose a rule first. It may issue a final rule without a notice of proposed rulemaking if it finds for good cause that such a notice is impracticable, unnecessary, or contrary to the public interest, as in a safety emergency, and the notice requirement itself does not apply to interpretative rules or general statements of policy.

The Federal Register is the daily publication where agencies publish proposed and final rules, and its contents are judicially noticed. The Code of Federal Regulations contains the complete and official text of agency regulations and is published once a year. The online Electronic Code of Federal Regulations, which updates daily, is an editorial compilation that is not an official legal edition of the Code of Federal Regulations, so a rule relied on for a legal question should be checked against the Federal Register amendments and the annual edition.

Advisory Material Is Not Binding

Binding rules are statutes, regulations, and airworthiness directives, which 14 CFR 39.3 calls legally enforceable rules. Most other FAA documents are guidance. The comparison below shows where each kind of document falls.

Advisory circulars describe an acceptable means of complying with a regulation, though not the only means, and an advisory circular’s contents carry no force and effect of law. Advisory Circular 120-92D, which covers safety management systems under Part 5, is one example. A document becomes binding when a regulation adopts it, and 14 CFR 36.6 shows how: it incorporates Annex 16 of the International Civil Aviation Organization by reference with the approval of the Director of the Federal Register.

FAA directives, which include orders and notices, are the agency’s primary means of issuing policies. Order 8900.1, for example, directs the work of aviation safety inspectors and treats the aviation industry’s use of it as reference only.

A Special Airworthiness Information Bulletin contains non-regulatory information and guidance that does not meet the criteria for an airworthiness directive. A Safety Alert for Operators contains safety information and may contain recommended actions, and an Information for Operators message contains information that operators may use to meet administrative or regulatory requirements, sometimes with recommended action.

Recommendations and Service Bulletins

NTSB safety recommendations are requests to regulators, operators, and others, and the NTSB has no authority to require that they be carried out. Federal law does require an answer, though. When the NTSB sends a recommendation to the Secretary of Transportation, the Secretary must give a formal written response within 90 days stating whether the Secretary intends to adopt all, part, or none of it. A response that adopts must include a timetable, a refusal must include reasons, and the NTSB makes recommendations and responses available to the public in an online database.

A manufacturer’s service bulletin is the manufacturer’s document, and labeling one “mandatory” does not make it mandatory under FAA regulations unless a rule requires it. A service bulletin becomes mandatory when an airworthiness directive requires compliance with it. An operator’s approved inspection program can also bind that operator to a bulletin, and programs used by Part 121 and Part 135 operators may require them to follow manufacturer-issued service bulletins.

International Frameworks

The International Civil Aviation Organization adopts international standards and recommended practices, which are published as annexes to the Convention on International Civil Aviation. Under Article 37 of the Convention, each contracting state undertakes to collaborate in securing the highest practicable degree of uniformity in regulations, and under Article 38 a state that does not bring its regulations into full accord with a standard must notify the organization of the differences.

The standards reach operators through national law. In the United States, FAA regulations do that work, and sometimes a regulation adopts an annex outright, as 14 CFR 36.6 does with Annex 16, Volume I, on aircraft noise. Complying with Part 5 also supports compliance with the International Civil Aviation Organization’s safety management standards in Annex 19.

In the European Union, the European Union Aviation Safety Agency operates under Regulation (EU) 2018/1139, whose principal objective is a high uniform level of civil aviation safety in the Union. The agency supports the European Commission by submitting opinions on proposed acts, and it separately issues certification specifications, acceptable means of compliance, and guidance material for applying the regulation. The agency’s division between acts and accompanying guidance looks similar to the FAA’s, but it is a separate legal system.

For a U.S. operator, the rules that bind are the federal laws and the regulations in Title 14, and International Civil Aviation Organization standards reach that operator through FAA regulations that adopt or implement them.