Definition
A designated radio frequency used at airports without an operating control tower (or when the tower is closed) on which pilots transmit position and intention reports to coordinate traffic with other pilots in the area. The CTAF for a given airport is published on charts and in the Chart Supplement and may be a UNICOM, MULTICOM, FSS, or tower frequency depending on the airport.
Plain English
It is the shared radio channel pilots use at airports that have no controller on duty. Everyone in the area listens and announces what they are doing so they can stay clear of each other.
Context Anchor
Used before taxi, takeoff, landing, and while flying near an airport without an operating tower controller.
Derivation
Common' because every pilot in the area uses the same frequency. 'Traffic Advisory' because pilots are advising each other of their position and intentions, rather than receiving instructions from a controller.
Why Pilots Care
It gives pilots a direct way to coordinate and reduce the chance of conflicts in the traffic pattern.
Intuition Check
CTAF is not air traffic control. No one on the frequency is separating you from other aircraft or clearing you to do anything. Pilots advise; they do not instruct.
Example Sentence 1
Five miles south of the field, the instructor told the student to make the first call on the CTAF and announce a left base entry for runway 27.
Example Sentence 2
Several aircraft were already monitoring the CTAF, so the student waited for a gap before transmitting.