Plain English Meaning

When the FAA draws the protected airspace around a VOR route, it assumes the airplane could drift up to 4.5 degrees off the published course because of small errors that add up — errors in the ground station, the cockpit receiver, and how exactly the pilot flies the line. The protected area is sized to cover all of that.

Full Definition

The combined accuracy tolerance used when designing VOR-based airways and routes, accounting for all sources of error in the VOR navigation system: ground station tolerance, receiver tolerance, (how precisely the pilot or the course), and aggregate error from these combined. The FAA uses a factor of plus or minus 4.5 degrees from the when establishing protected along .