Definition
The combined navigational error allowance used in RNAV procedure design, made up of three components: path definition error (how accurately the path is described in the navigation database), flight technical error (how well the pilot or autopilot follows the path), and navigation system error (the inherent error of the navigation sensors, such as GPS or DME/DME). Total system accuracy defines the cross-track tolerance assumed when establishing obstacle clearance areas around an RNAV route or procedure.
Plain English
It's the total amount of side-to-side error the FAA assumes when they draw the protected airspace around an RNAV route. It adds up errors from the chart data, the pilot's tracking, and the navigation equipment itself.
Context Anchor
Seen in IFR en route procedure design, especially when explaining how wide obstacle clearance areas must be around a route.
Derivation
“Total” means all parts taken together. “System” means the combined equipment, path information, and aircraft tracking involved in navigation. “Accuracy” means closeness to the intended path, not perfection.
Why Pilots Care
It sets the size of the safety buffer around the intended route so obstacles remain safely outside the flight path despite normal errors.
Grounding Statement
Think of it as the expected gap between the course drawn for the aircraft and where the aircraft may actually be while flying it.
Intuition Check
Do not read “accuracy” here as only the accuracy of one device, such as GPS. In this context, total system accuracy means the combined accuracy of the whole navigation-and-flying system.
Example Sentence 1
The width of the obstacle clearance area on this RNAV route is based on total system accuracy, so staying within the magenta line keeps the aircraft inside protected airspace.
Example Sentence 2
Procedure designers apply total system accuracy to establish the boundaries of the en route obstacle clearance area.