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United States Department of Transportation United States Department of Transportation

Advisory Circulars (ACs)

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Advisory Circulars (ACs) search results
Number Title Status Office Date
20-135A Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria

This advisory circular (AC) provides guidance for powerplant fire testing and recognizes the Society of Automotive Engineers (SAE) Aerospace Standard (AS) 6826, Powerplant Fire Test Standards, as an acceptable Means of Compliance (MoC) for demonstrating compliance to the applicable regulations specified in Appendix A.

Active AIR-625 2025-09-29
33.67-1 Engine Fuel Systems

This advisory circular (AC) provides guidance for demonstrating compliance with the
requirements of Title 14, Code of Federal Regulations (14 CFR) Section 33.67, Fuel
system.

Active AIR-625 2024-05-20
33.70-4 Fatigue Life of Nickel Powder Rotating Life-Limited Parts

This advisory circular (AC) provides guidance that may be used to demonstrate compliance with Title 14, Code of Federal Regulations (14 CFR) 33.70 for rotating life-limited engine parts made of nickel powder.

Active AIR-625 2023-08-15
20-29C Approval and Use of Fuel System Icing Inhibitors (FSII)

This advisory circular (AC) describes an acceptable method to demonstrate compliance with Title 14, Code of Federal Regulations (14 CFR) §§ 23.2620(a)(1), 25.1583(b)(1), 27.1583(b)(1), 29.1583(b)(1), 33.7(b)(2), and 33.7(c)(2) regarding the requirements for the approval and use of Fuel System Icing Inhibitors (FSII) in engines and aircraft.

Active AIR-625 2024-03-27
33-12 Geometry and Dimensional Considerations for Comparative Test and Analysis for Turbine Engine and Auxiliary Power Unit (APU) Replacement, and Repaired Parts

This advisory circular (AC) provides guidance to support the development of technical data needed to show that an engine or APU replacement part complies with the airworthiness requirements under test and computation, per Title 14, Code of Federal Regulations (14 CFR) 21.303, using the comparative test and analysis approach.

Active AIR-625 2025-09-08
20-197 Turbine Engine and Airframe Sensor Icing Compliance

This advisory circular (AC) describes an acceptable method for demonstrating compliance with title 14, Code of Federal Regulations (14 CFR) 33.28, 33.68, 33.75,33.89, a nd 33.91, concerning mixed phase, ice crystal icing (ICI), and other icingconditions for engine inlet sensors.

Active AIR-625 2025-06-18
33.15-1A Manufacturing Process of Premium Quality Titanium Alloy Rotating Engine Components Active AIR-625 2025-09-08
33.17-1B Engine Fire Protection § 33.17

This advisory circular (AC) provides definitions, guidance, and acceptable methods, but not the only methods, to demonstrate compliance with the engine fire protection requirements of title 14 Code of Federal Regulations (14 CFR 33.17).

Active AIR-625 2025-05-20