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, airborne receiver tolerance, flight technical error (how precisely the pilot or autopilot tracks the course), and aggregate error from these combined. The FAA uses a total system accuracy factor of plus or minus 4.5 degrees from the course centerline when establishing protected obstacle clearance areas along VOR airways.
Plain English
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.
Context Anchor
Seen in instrument procedure and airway design discussions, especially when explaining VOR en route obstacle clearance areas.
Why Pilots Care
It sets the size of the protected airspace around airways, directly affecting obstacle clearance margins.
Grounding Statement
A small angle near the VOR station is only a small sideways distance, but the same angle many miles away covers much more sideways distance.
Intuition Check
Do not read “accuracy factor” as a cockpit correction or a guarantee that the airplane is always only 4.5 degrees from course. Here it means a design allowance used to protect airspace around a VOR route.
Example Sentence 1
Victor airway widths are based on the total VOR system accuracy factor of plus or minus 4.5 degrees from the centerline.
Example Sentence 2
Procedure designers used the total VOR system accuracy factor to verify terrain clearance at the outer edge of allowable course deviation.