Definition
A value, expressed in nautical miles, that defines the lateral navigation accuracy an aircraft must maintain for at least 95 percent of the flight time on a given route, procedure, or airspace segment. RNP-X means the aircraft's position must remain within X nautical miles of the intended track 95 percent of the time. The number replacing X identifies the level: smaller numbers mean tighter accuracy. For example, RNP 1 requires accuracy within 1 NM of track, RNP 0.3 requires accuracy within 0.3 NM, and RNP 2 requires accuracy within 2 NM.
Plain English
A rule that says how close to the planned route the aircraft has to stay. The number after RNP is how many nautical miles of error are allowed, and the aircraft has to stay inside that limit at least 95 percent of the time. A smaller number means stricter accuracy.
Context Anchor
You may see RNP-X in FAA glossary material, route requirements, approach descriptions, aircraft equipment approvals, and navigation procedure notes.
Derivation
Required' means it is mandated, not optional. 'Navigation Performance' refers to how accurately the aircraft can determine and hold its position. Putting these together: the level of navigation accuracy the aircraft is required to deliver. The number X simply quantifies that requirement in nautical miles.
Why Pilots Care
Determines which precise routes and approaches an aircraft is allowed to fly based on its navigation equipment capabilities.
Intuition Check
Do not read the X as a mystery rating or a generic label. It stands for the specific RNP level or type that the route or procedure requires.
Example Sentence 1
The approach was charted as RNP 0.3, so the crew confirmed the aircraft was approved for that level before beginning the procedure.
Example Sentence 2
RNP-1 airspace lets approved aircraft fly more direct paths than those limited to conventional ground-based navigation.