__NOTOC__ Advisory circular (AC) refers to a type of publication offered by the Federal Aviation Administration (FAA) to "provide a single, uniform, agency-wide system … to deliver advisory (non-regulatory) material to the aviation community." Advisory circulars are now harmonized with soft law Acceptable Means of Compliance (AMC) publications of EASA, which are nearly identical in content. The FAA's Advisory Circular System is defined in FAA Order 1320.46D.
By writing advisory circulars, the FAA can provide guidance for compliance with airworthiness regulations, pilot certifications, operational standards, training standards, and any other rules within the 14 CFR Aeronautics and Space title, aka 14 CRF or FARs. The FAA also uses advisory circulars to officially recognize "acceptable means, but not the only means," of accomplishing or showing compliance with airworthiness regulations.David B. Walen FAA, Civil Aircraft System Safety and Electromagnetic Compatibility, November 16, 2010, p. 6. "Compliance with Regulations: FAA Guidance for compliance with airworthiness regulations published within Advisory Circulars (ACs) | Define acceptable, but not the only, means to comply with the airworthiness regulations | For example, AC 25.1309-1A describes acceptable means for showing compliance with 14 CFR 25.1309" Advisory circulars may also contain explanations, clarifications, best practices, or other information of use to the aviation community. Note: This is verbatim from FAA Order 1320.46D.
Usage Advisory circulars can recognize industry standards from SAE (ARP), RTCA (DO), and others. With harmonization of technical content and guidance between EASA and the FAA, later advisory circulars also identify corresponding EUROCAE (ED) publications.AC 20-115D, FAA, Office AIR-134, 2017. "The technical content of this AC is as far as practicable harmonized with European Aviation Safety Agency (EASA) AMC 20-115D, equally based on ED-12C/DO-178C."
Some advisory circulars are only a few pages long and do little more than reference a recommended standard; for example, AC 20-152 referencing DO-254.AC 20-152, FAA, 2007. Others, like AC 20-115C/D, are considerably longer; in this case including guidance on how to transition from DO-178 revision B to CAC 20-115D, FAA, Office AIR-134, 2017. while AC 20-152A adds several new objectives to an otherwise unchanged DO-254.
Relation to regulations Generally informative in nature, Advisory Circulars are neither binding nor regulatory; yet some have the effect of de facto standards or regulations.Approach, Volume 31, Issue 3, Naval Safety Center, 1985 - Aeronautics, p. 25. "Advisory Circulars, as their title implies, are informative in nature. However, some are actually de facto regulation because they explain what is required to comply with the FAA's or keep the Feds smiling." The FAA establishes regulation of U.S. civil airspace through issuance of Federal Aviation Regulations (FAR). Issuing or amending FARs requires a potentially lengthy period of public commentary and agency reflection on proposed rule making before they may be issued for enforcement. In practice, advisory circulars have essential roles for public compliance with the regulations. The FAA relies on the advisory circular system to "Provide an acceptable, clearly understood method for complying with a regulation" "Standardize implementation of a regulation or harmonize implementation for the international aviation community" "Resolve a general misunderstanding of a regulation" "Help the industry and FAA effectively implement a regulation"FAA Order 1320.46D, p. 3-1
In contrast with the lengthy processes of FARs, advisory circulars may be published with little or no advanced notice or distribution. A concern is that the content of advisory circulars should not have the effect of de facto amendments to regulations. In general, the FAA may not "use an AC to add, reduce, or change a regulatory requirement."FAA Order 1320.46D, p. 3-5
+ Examples of Published Advisory Circulars Advisory Circular Title Referenced StandardsAC 00-69Best Practices for Airborne Software Development Assurance Using and AC 00-71Best Practices for Management of Open Problem Reports (OPRs)AC 00-72Best Practices for Airborne Electronic Hardware Design Assurance Using and AC 20-115Airborne Software Development Assurance Using and ED-12C/DO-178CED-215/DO-330ED-218/DO-331ED-217/DO-332ED-216/DO-333AC 20-136Aircraft Electrical and Electronic System Lightning ProtectionRTCA DO-160 §22AC 20-148Reusable Software ComponentsAC 20-152ADesign Assurance Guidance for Airborne Electronic HardwareRTCA DO-254AC 20-170Integrated Modular Avionics Development. Verification, Integration and ApprovalRTCA DO-297AC 20-189 Management of Open Problem Reports (OPRs)AC 20-1317The Certification of Aircraft Electrical and Electronic Systems for Operation in the High Radiated Fields (HIRF) EnvironmentAC 25.1309-1System Design and AnalysisARP4754, ARP4761AC 20-174Development of Civil Aircraft and SystemsARP4754AAC 43.13-1BAcceptable Methods, Techniques, and Practices - Aircraft Inspection and RepairAC 70-1Outdoor Laser OperationsAC 91-57BException for Limited Recreational Operations of Unmanned Aircraft (relevant to Regulation of UAVs in the United States)AC 107-2Small Unmanned Aircraft Systems (sUAS) (contains 14 CFR part 107 guidance). 49 U.S.C. § 44809
See also Airworthiness Directive (in comparison, airworthiness directives are legally enforceable rules)
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