Definition
The combined difference between the aircraft's actual position and the position the navigation system commands it to be in, made up of three components: path definition error (how accurately the desired path is described in the navigation database), flight technical error (how precisely the pilot or autopilot follows the commanded path), and navigation system error (how accurately the navigation equipment determines the aircraft's position).
Plain English
The total amount by which the aircraft is off from where it is supposed to be on an RNAV route, adding together every source of error along the way: errors in the stored route, errors in flying the route, and errors in figuring out where the aircraft actually is.
Context Anchor
Seen in RNAV departure and performance-based navigation discussions, especially when checking whether the aircraft can stay within the protected path for the procedure.
Derivation
“Error” comes from a Latin word meaning “to wander” or “to stray.” That fits the aviation meaning: the aircraft has strayed from the exact path it was meant to follow. “Total” matters because this term counts all the contributing sources together, not just one cause.
Why Pilots Care
It determines whether the aircraft meets the accuracy needed to safely fly RNAV and RNP routes without violating protected airspace.
Grounding Statement
Total system error is the real-world gap between where the airplane is and where the procedure expects it to be.
Intuition Check
Do not read “error” here as only a pilot mistake. Total system error means the combined path error from the navigation system, the defined route, and how accurately the aircraft is flown.
Example Sentence 1
To fly an RNAV 1 departure, total system error must remain within 1 NM of the centerline 95 percent of the flight time.
Example Sentence 2
High total system error on the approach triggered an alert and required the pilot to revert to conventional navigation.