Definition
The lateral dimensions of the protected airspace along an en route airway or route, measured outward from the route centerline. Route widths define the primary obstacle clearance area (typically 4 NM either side of centerline within 51 NM of the navigation facility) and the secondary area (an additional 2 NM either side beyond the primary area). Beyond 51 NM from the facility, the protected area splays outward at a defined angle to account for navigation signal divergence.
Plain English
How wide the protected corridor is on each side of an airway's centerline. The FAA guarantees obstacle clearance inside this corridor, with full clearance in the inner zone and reduced clearance in the outer zone.
Context Anchor
Seen in instrument procedure design and en route obstacle-clearance discussions, especially when explaining primary and secondary protected areas along airways and other instrument routes.
Why Pilots Care
Determines how much lateral deviation from centerline remains protected from terrain and obstacles during IFR enroute flight.
Analogy
A charted route line is like the center stripe of a road. The route width is the usable lane area on both sides of that stripe where protection has been planned.
Grounding Statement
Picture the route as a corridor in the sky, with a centerline and a planned amount of protected space on each side.
Intuition Check
Do not read route widths as the thickness of the printed line on a chart. Here, route widths mean the real protected airspace measured sideways from the route centerline.
Example Sentence 1
The instructor explained that route widths expand beyond 51 NM from the VOR because navigation signal accuracy decreases with distance.
Example Sentence 2
When deviating slightly for weather, the crew stayed inside the secondary route widths to maintain obstacle clearance.