Plain English Meaning

The aircraft watches its own navigation accuracy in real time and tells the pilots if it is no longer accurate enough for the route or approach they are flying.

Full Definition

A required capability of an RNP (Required Navigation Performance) system in which the aircraft's navigation equipment continuously checks how accurately it is determining its position along the flight path and warns the crew if that accuracy falls below the level required for the procedure being flown. It is the feature that distinguishes RNP operations from ordinary RNAV operations.

Context Anchor

Seen in RNP procedures, especially where the aircraft must prove it can within a stated navigation limit during the operation.