Route width

This regulation establishes how wide an approved route corridor is for Part 121 airline operations.

For routes that follow established Federal airways, foreign airways, or advisory routes (for flag carriers), the route width is simply whatever width those airways already have—typically 4 nautical miles on each side of centerline for most airways.

For routes that don't follow published airways, the FAA determines an appropriate width based on five factors: terrain clearance needs, minimum altitudes, available navigation aids, how busy the airspace is, and air traffic control procedures in the area. These custom route widths are then written into the airline's operations specifications.

This matters because pilots must be able to navigate within the route boundaries, and the route width affects obstacle clearance calculations, fuel planning, and what happens if you deviate from course. Wider routes provide more lateral navigation tolerance.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*