Definition
An FAA Advisory Circular that provides recommended standards, practices, and procedures for operating at airports without an operating control tower. It covers traffic pattern entry and departure, radio communication phraseology on the Common Traffic Advisory Frequency (CTAF), right-of-way considerations, and safe coordination between aircraft when no controller is present.
Plain English
An FAA guidance document that tells pilots how to safely fly into and out of airports that don't have a control tower, including how to enter the traffic pattern and what to say on the radio.
Context Anchor
You may see AC 90-66 referenced when studying airport operations, especially procedures at non-towered airports.
Derivation
An 'Advisory Circular' (AC) is the FAA's way of issuing non-regulatory guidance — 'advisory' meaning it advises rather than commands, and 'circular' meaning a document distributed to the public. The number '90-66' identifies its subject series (90 = Air Traffic and General Operating Rules) and its specific document number. Knowing it's advisory helps explain why it gives recommended practices rather than mandatory rules.
Why Pilots Care
Following the guidance helps maintain orderly traffic flow and reduces the risk of mid-air collisions at busy uncontrolled fields.
Intuition Check
Do not read “advisory” as “unimportant.” AC 90-66 is guidance, not a regulation by itself, but it describes practices pilots are expected to know and use for safe operations.
Example Sentence 1
Before flying into the small grass strip, she reviewed AC 90-66 to refresh herself on the proper traffic pattern entry and CTAF call procedures.
Example Sentence 2
AC 90-66 recommends that pilots announce their position and intentions on the common traffic advisory frequency.