Definition
An air traffic control automation tool that calculates and displays spacing instructions to en route controllers so that aircraft arrive at a downstream point — typically a meter fix feeding a busy arrival airport — at the correct intervals to support orderly sequencing into the terminal area.
Plain English
A computer tool that helps en route controllers space aircraft out properly while they are still cruising, so they arrive at the handoff point to the approach controllers in a smooth, evenly spaced line.
Context Anchor
Seen in FAA acronym lists, traffic-management discussions, and ATC delay or arrival-flow planning.
Derivation
En route comes from French, meaning 'on the way' — the cruise phase between departure and arrival. Spacing refers to the distance or time gap between aircraft. Together, the program manages how far apart aircraft are while still on the way to their destination.
Why Pilots Care
Reduces delays and prevents airspace congestion during busy periods.
Intuition Check
Do not read ESP as a cockpit system or pilot-controlled tool. In this context, it is an air traffic control program for spacing aircraft.
Example Sentence 1
The en route spacing program prompted the controller to ask us to slow to 280 knots to absorb a delay into the arrival.
Example Sentence 2
During peak traffic the ESP helped keep arrivals sequenced without vectoring.