Definition
A method of separating aircraft by spacing them along the same flight path, expressed in either time or distance, so that one aircraft remains a required interval ahead of or behind another along the route of flight.
Plain English
Keeping two aircraft apart by putting space between them along the route they are flying — one in front, one behind — measured in minutes or miles.
Context Anchor
Used in air traffic control, especially when controllers space aircraft on routes, approaches, departures, or oceanic and non-radar segments.
Derivation
Longitudinal comes from the Latin longitudo, meaning length. Here it refers to separation measured along the length of the route — front-to-back spacing — as opposed to side-to-side (lateral) or up-and-down (vertical) separation.
Why Pilots Care
Maintains safe following distances to prevent collisions and reduce wake turbulence encounters.
Intuition Check
Longitudinal separation does not mean aircraft are simply separated in any direction. It specifically means spacing along the direction of travel, like front-to-back spacing on a route.
Example Sentence 1
Center applied longitudinal separation by issuing a speed reduction to the trailing aircraft until the required ten-mile spacing was established.
Example Sentence 2
ADS-B equipage allows controllers to apply three nautical miles of longitudinal separation in approved airspace.