Definition
A coding method used in the ARINC 424 navigation database standard in which every leg of a published instrument procedure is described by a two-letter code that defines both the path the aircraft is to fly and the terminator that ends the leg. The path describes the geometric track (such as a course, heading, or arc), and the terminator describes what causes the leg to end (such as reaching a fix, an altitude, an intercept, or a distance). Together, these two-letter path terminator codes (for example, TF for Track to Fix, CA for Course to Altitude, VA for Heading to Altitude) allow an FMS or RNAV system to fly a published procedure exactly as the procedure designer intended.
Plain English
It is the standard way that flight management computers describe each segment of a published procedure: one part says how to fly the segment, and the other part says when that segment is finished and the next one begins.
Context Anchor
Seen when learning how instrument procedures are coded into aviation navigation databases and then displayed or flown by cockpit navigation equipment.
Derivation
Path' refers to the track the aircraft flies along the ground or through the air. 'Terminator' comes from the Latin terminare, meaning 'to end or limit.' In this context, the terminator is simply what marks the end of that path segment, after which the next leg begins.
Why Pilots Care
Different path terminators produce different aircraft behavior. A leg that ends at an altitude flies until the altitude is reached, while a leg that ends at a fix flies until the fix is crossed. Knowing this helps a pilot understand why the FMS sequences legs the way it does and why a procedure may behave differently than expected if the wrong leg type is loaded or flown.
Analogy
It is like a driving instruction that says, “Drive north on this road until you reach the bridge.” “Drive north on this road” is the path; “until you reach the bridge” is the terminator.
Grounding Statement
Each coded leg needs both a way to fly and a clear condition that says the leg is complete.
Intuition Check
Do not read “terminator” as a device or a person. In this context, it means the ending condition for a navigation leg.
Example Sentence 1
The departure procedure was coded with a CA leg, so the autopilot held the assigned heading until reaching the altitude that terminated the leg.
Example Sentence 2
Using the path and terminator concept, a holding pattern is coded as a racetrack path that terminates after a specified time or distance.