Definition
An ARINC 424 path and terminator leg type in which the aircraft flies a specified course until reaching a defined altitude, at which point the leg ends and the next leg begins. The leg has no fixed endpoint in space; the terminator is the altitude itself.
Plain English
A leg of a procedure that says 'fly this heading or course until you reach this altitude, then move on to the next instruction.' What ends the leg is the altitude, not a point on the map.
Context Anchor
Seen in instrument procedure database coding and flight-management-system descriptions of departures, arrivals, and missed approach paths.
Derivation
Path and terminator' is the ARINC 424 naming convention used by avionics databases. The two-letter code 'CA' encodes the path (Course) and the terminator (Altitude). Knowing this makes the alphabet of leg types — CA, CF, CI, DF, FA, VA, and so on — readable rather than mysterious.
Why Pilots Care
It guarantees the aircraft reaches a required height before any turn, protecting against obstacles and meeting procedure requirements.
Grounding Statement
Picture the airplane tracking a line across the ground while climbing; the leg ends the moment the required altitude is reached.
Intuition Check
Do not read course as a school class or merely the direction the nose is pointed; here it means the intended path over the ground. Do not assume the leg ends at a fixed point; it ends when the specified altitude is reached.
Example Sentence 1
After takeoff, the departure procedure begins with a CA leg: fly runway heading until reaching 2,000 feet, then turn on course.
Example Sentence 2
The navigation system ends the CA leg automatically once the altitude constraint is met.