Definition
A path-and-terminator leg type used in RNAV procedure coding that defines a specified magnetic course to be flown until a specified altitude is reached. The leg has no fixed end point in space; it terminates the moment the aircraft crosses the coded altitude, after which the next leg in the procedure begins.
Plain English
Fly this heading on this course until you climb (or descend) through this altitude. As soon as you hit that altitude, this leg is finished and the next instruction takes over.
Context Anchor
Seen in RNAV and instrument procedure design, especially when reading about path and terminator legs used by a navigation system.
Derivation
From the ARINC 424 path-and-terminator coding system used by avionics designers. Each leg type is named by its path (what you fly) and its terminator (what ends it). Here the path is a Course and the terminator is an Altitude — so 'CA'. Knowing this pattern helps decode the other leg types (CF, CI, CR, VA, etc.) the same way.
Why Pilots Care
It guarantees the aircraft reaches a safe altitude before any turn, protecting against terrain or obstacles during climbs in instrument conditions.
Intuition Check
Course does not mean a training class here; it means the direction or path to fly. Altitude does not describe where the leg starts; it is the condition that ends the leg.
Example Sentence 1
After takeoff, the SID coded a CA leg requiring runway heading until 2,000 feet before the first turn.
Example Sentence 2
On the missed approach the CA leg keeps the aircraft on the published course until it reaches the minimum climb altitude.