Definition
A VD leg is an ARINC 424 path-and-terminator leg type in which the aircraft flies a specified magnetic heading until it reaches a defined DME slant-range distance from a referenced DME station, at which point the leg terminates and the next leg begins. The 'V' identifies the path as a heading (not a track), and the 'D' identifies the terminator as a DME distance.
Plain English
Fly the assigned heading until you are a certain distance from a named DME station, then start the next part of the procedure.
Context Anchor
Seen in instrument-procedure design and flight-management-system database coding, especially in discussions of path and terminator legs.
Derivation
In the ARINC 424 leg-coding system used by avionics databases, each leg is named by two letters: the path flown and the terminator that ends it. 'V' stands for heading (a vector through the air), and 'D' stands for DME distance. So 'VD' literally means 'heading path, DME-distance termination.'
Why Pilots Care
Allows the aircraft to reach the correct position along the intended track before turning or joining the next segment, maintaining procedure compliance and separation.
Grounding Statement
Picture holding the assigned heading while the DME number changes, then starting the next procedure segment when the published distance appears.
Intuition Check
Do not read “termination” as the end of the whole procedure. Here it means the condition that ends this one leg. Do not read a VD leg as “go directly to a fix.” It means hold a heading until a specified distance is reached.
Example Sentence 1
After takeoff, the SID coded a VD leg requiring us to fly heading 090 until 8 DME from the field, then turn on course.
Example Sentence 2
After departure the aircraft flew a VD leg until reaching 15 DME, then turned to intercept the airway.