Definition
An Advisory Circular (AC) is a non-regulatory document issued by the FAA to provide guidance, recommended practices, and methods of compliance with the Federal Aviation Regulations. ACs are numbered to correspond with the Title 14 CFR part they relate to (for example, AC 61-65 relates to 14 CFR Part 61).
Plain English
An official FAA document that explains how to do something correctly or how to meet a rule. It is guidance, not a rule itself, but it shows the FAA's accepted way of doing things.
Context Anchor
Seen in aircraft electrical-system discussions, especially when learning what type of power a piece of equipment needs.
Derivation
From the Latin 'circularis,' meaning 'circular' -- a document circulated widely to many readers. 'Advisory' means it offers advice rather than enforces a rule. Together: a widely-circulated advice document.
Why Pilots Care
Many aircraft instruments and avionics require stable AC power; understanding AC helps pilots diagnose electrical failures and interpret system schematics.
Intuition Check
Do not confuse AC with air conditioning in this glossary context. Here, AC means alternating current, a type of electrical power.
Example Sentence 1
The instructor pointed to AC 00-6, the FAA's advisory circular on aviation weather, for a clearer explanation of frontal systems.
Example Sentence 2
Before flight the pilot verified that both AC and DC buses showed normal voltage on the electrical system display.