Definition
A measure of how accurately an aircraft's flight management system (FMS) or area navigation (RNAV) computer can calculate and maintain the aircraft's position along a defined flight path. It reflects the navigation computer's ability to meet a specified accuracy standard, expressed as a lateral deviation value the system is expected to hold under normal conditions.
Plain English
How well the aircraft's navigation computer can figure out where the airplane is and keep it on the planned route within a stated margin of error.
Context Anchor
Seen in instrument flying discussions of GPS, flight management systems, and area navigation procedures where the airplane’s computer is providing course guidance.
Derivation
“Computer” comes from a word meaning “to calculate,” and “navigation” means finding and following a path. Together, the phrase points to the computer’s ability to calculate where the aircraft is and guide it along the intended path.
Why Pilots Care
Determines whether an aircraft can legally and safely conduct RNAV or RNP approaches and departures.
Analogy
It is like a map app showing your location: if the blue dot is very accurate, you can trust the route guidance; if the location is uncertain, the route may no longer be dependable.
Grounding Statement
In flight, computer navigation performance is good when the aircraft’s systems can determine position closely enough for the route or approach being flown.
Intuition Check
Do not read “performance” here as aircraft climb, speed, or engine performance. Here it means the quality and reliability of the navigation computer’s position and guidance information.
Example Sentence 1
Before flying the RNAV approach, the crew verified that the aircraft's computer navigation performance met the accuracy required for the procedure.
Example Sentence 2
Pilots verify computer navigation performance before entering RNAV routes in the flight plan.