Definition
The reference line down the middle of an RNP (Required Navigation Performance) flight path that defines the intended lateral track the aircraft is meant to follow. RNP containment requirements are measured as a distance either side of this centerline, expressed in nautical miles.
Plain English
The imaginary line that marks the exact track the aircraft is supposed to fly. Performance limits — how far the aircraft is allowed to drift — are measured outward from this line on either side.
Context Anchor
Seen in Required Navigation Performance procedures, especially when describing how closely the aircraft must stay on the intended path during an approach or route segment.
Why Pilots Care
Staying close to the flightpath centerline keeps the aircraft inside required navigation tolerances and clear of obstacles.
Grounding Statement
Picture the planned course as a thin invisible line in the sky; the flightpath centerline is the middle of that line.
Intuition Check
Do not think of this as a painted runway centerline. In this context, the flightpath centerline is an invisible navigation line that marks the intended path through the air.
Example Sentence 1
On the RNP approach, the crew monitored cross-track deviation to ensure the aircraft stayed close to the flightpath centerline.
Example Sentence 2
The flight management system continuously monitors position relative to the flightpath centerline.