Definition
A path and terminator leg type used in RNAV procedure coding in which the aircraft flies a specified magnetic heading until it intercepts the course of the following leg. The leg has no fixed termination point of its own; it ends when the navigation system detects interception of the next leg's defined path. VI legs are commonly used on departures and missed approaches to fan traffic onto a course or to transition from a heading-based segment onto a defined track.
Plain English
The pilot flies a specific compass heading and keeps flying it until the aircraft crosses the next segment of the route, at which point the aircraft turns to follow that next segment. There is no distance, time, or altitude that ends this leg — only crossing the next course does.
Context Anchor
Seen in instrument procedure design and GPS or flight management system coding, especially when a procedure needs the aircraft to leave one path and join another by flying a heading first.
Derivation
The two-letter codes used for these legs come from the ARINC 424 navigation database standard. The first letter describes the path flown (V = heading, vector), and the second letter describes how the leg ends (I = intercept). So 'VI' literally reads as 'fly a heading, end at an intercept.'
Why Pilots Care
Allows a smooth, predictable transition from radar vectors onto the final approach course without overshooting or requiring manual intervention.
Analogy
It is like driving straight on one street until you meet a marked road you are supposed to turn onto. The important part is not the distance you drive first, but joining the correct road when you reach it.
Intuition Check
Do not read “heading” as the same thing as the path over the ground. Here, heading means the direction the aircraft is pointed until it intercepts the next procedure path.
Example Sentence 1
After takeoff, the SID coded a VI leg requiring the crew to fly heading 270 until intercepting the 350 radial from the VOR.
Example Sentence 2
After receiving vectors, the FMS executed the VI leg and captured the inbound course automatically.