Definition
An ARINC 424 path and terminator leg in which the aircraft flies a specified magnetic heading until it reaches a defined DME (Distance Measuring Equipment) distance from a referenced navaid. The leg ends when the DME distance is reached, regardless of position or track.
Plain English
A segment of an instrument procedure where the aircraft flies a set heading until it is a certain distance from a ground station, then the segment ends.
Context Anchor
Seen in the coded leg types used to build instrument departure, arrival, and approach procedures.
Derivation
In the ARINC 424 coding system, each leg type is given a two-letter code. 'V' designates a heading leg (think 'vector'), and 'D' designates termination at a DME distance. So 'VD' literally means 'heading until DME distance.'
Why Pilots Care
It provides a precise, direct routing that simplifies navigation and keeps the aircraft on the published procedure without unnecessary turns.
Grounding Statement
Picture holding a published heading while watching the distance readout change; when it reaches the published number, the VD leg is complete.
Intuition Check
Do not read “leg” as a part of the airplane; here it means one segment of a flight path. A VD leg is controlled by heading and distance, not by time or by a visual landmark.
Example Sentence 1
The departure procedure included a VD leg requiring the crew to fly heading 090 until 12 DME from the airport navaid before turning on course.
Example Sentence 2
The procedure used a VD leg to route the aircraft straight to the missed approach point.