Definition
A real-time measurement, calculated by the aircraft's navigation system, of how accurately the aircraft is currently determining its own position. It is expressed as a radius, in nautical miles, within which the aircraft's true position is statistically expected to lie 95% of the time. ANP is compared against a Required Navigation Performance (RNP) value to confirm the navigation system is accurate enough for the current phase of flight.
Plain English
A live readout from the navigation system telling the pilot how confident it is about where the aircraft actually is. A smaller number means a tighter, more accurate fix.
Context Anchor
Seen on GPS or flight management system pages when checking whether the aircraft is meeting the navigation accuracy needed for a route, arrival, approach, or oceanic segment.
Derivation
Three plain English words. 'Actual' means what is happening right now, not what is required or estimated. 'Navigation performance' means how well the system is doing its job of locating the aircraft. So ANP is the system's honest, current report on its own positioning accuracy.
Why Pilots Care
It confirms whether the aircraft's position data is reliable enough to continue on its planned route or approach.
Analogy
Think of ANP like a circle around your airplane’s shown position. A small circle means the system is more confident about where you are; a large circle means more uncertainty.
Intuition Check
“Actual” does not mean the required or planned accuracy. Here it means the navigation performance the aircraft system estimates it is achieving right now.
Example Sentence 1
Before commencing the RNP approach, the crew confirmed ANP was 0.15 nautical miles, well within the 0.30 required.
Example Sentence 2
An ANP of 0.3 nautical miles gave the crew high confidence in the aircraft's computed position.