Definition
The lateral displacement from a desired course, measured as an angle that fans outward from the navigation station rather than as a fixed distance. Because the course is angular, the same needle deflection on a CDI represents a small distance from centerline when close to the station and a much larger distance when far away.
Plain English
How far you are off course, measured as an angle spreading out from the station. The same amount of needle swing means you are only slightly off when near the station, but well off when far from it.
Context Anchor
Seen in VOR/DME RNAV discussions when comparing older angle-based course guidance with systems that show distance-based guidance.
Derivation
Angular comes from the Latin angulus, meaning corner or angle. Here it signals that the deviation is measured as an angle opening from a point (the station), not as a fixed lateral distance. That is why the off-course distance grows as you fly farther from the station.
Why Pilots Care
It determines how precisely the aircraft must be flown to remain within protected airspace and on the desired track during instrument procedures.
Analogy
Think of a flashlight beam. The beam is narrow near the bulb but spreads wider the farther it shines. Angular course width works the same way: the course is tight near the station and fans out with distance.
Grounding Statement
A small angle close to a VOR station may put you only slightly off the path, while the same angle far from the station may put you much farther away from it.
Intuition Check
“Width” does not mean a fixed strip of airspace here. In this term, the course width spreads out with distance because it is measured by angle.
Example Sentence 1
Because of angular course width deviation, the pilot recognized that a half-scale CDI needle 80 miles from the VOR meant a much larger off-course distance than the same deflection close in.
Example Sentence 2
Reducing angular course width deviation to less than half scale kept the aircraft inside the required lateral limits during the approach.