Definition
An AF leg is an RNAV path-and-terminator leg type that defines a constant-radius arc around a designated navigation reference (the arc center), terminating at a specified fix. The aircraft's flight management system flies the curved path at the published radius until reaching the terminating waypoint.
Plain English
A curved flight path that follows a circle of fixed distance around a chosen point, ending at a named waypoint.
Context Anchor
Seen in RNAV procedure design, flight management system coding, and FAA explanations of path-and-terminator legs.
Derivation
In ARINC 424 path-terminator coding, each leg type is named by two letters: the first describes the path (how you get there), the second describes the terminator (what ends the leg). 'A' stands for Arc, 'F' stands for Fix. So AF literally means 'fly an arc, end at a fix.'
Why Pilots Care
It enables precise curved routing to join the final approach course without requiring a straight segment from every direction.
Intuition Check
Do not read “leg” as a physical part of the airplane. In this context, a leg is one segment of a procedure. Do not read “AF” as “Air Force” here. In this context, AF means Arc to a Fix.
Example Sentence 1
The arrival procedure included an AF leg that kept the aircraft 12 NM from the VOR until intercepting the final approach course.
Example Sentence 2
After intercepting the arc, the aircraft flew the AF leg until reaching the intermediate fix.