Definition
A path-and-terminator (path terminator) leg type used in coded instrument procedures in which the aircraft flies a specified course until it reaches a defined DME distance from a referenced navigation aid. The leg is defined by two elements: the course to be flown and the DME distance from a specific station that ends (terminates) the leg.
Plain English
Fly this heading on the chart until you are a set number of miles from a named ground station, then the leg is over and the next instruction begins.
Context Anchor
Seen in instrument procedure design and navigation database descriptions for path and terminator legs.
Derivation
DME stands for Distance Measuring Equipment, a ground station that tells an aircraft how far it is from that station. 'Path terminator' is the design term for a two-letter code (here, CD) that tells the flight management system both how to fly the leg (the path) and what ends it (the terminator). The 'C' is the course; the 'D' is the DME distance that closes it out.
Why Pilots Care
Ensures the aircraft reaches the correct altitude and position for the next segment without overshooting protected airspace.
Grounding Statement
Picture the airplane holding a published direction while the DME distance counts up or down to the required value.
Intuition Check
Do not read “course” as a training class or general route here. In this term, course means the direction or path the aircraft is meant to follow, and the leg ends at a specific DME distance, not at a visual checkpoint or after a set time.
Example Sentence 1
After takeoff, the SID coded a CD leg requiring the crew to fly runway heading until 6 DME from the field, then turn on course.
Example Sentence 2
The missed approach includes a CD leg outbound on the localizer until reaching 5 DME before turning.