Definition
The imaginary lines running lengthwise down the exact middle of runways, taxiways, or final approach courses, used as the primary lateral reference for alignment during taxi, takeoff, approach, and landing. On runways and taxiways, they are marked with painted stripes; for instrument approaches, they are defined electronically by the navigation aid serving that runway.
Plain English
The straight lines down the middle of a runway, taxiway, or approach path that pilots line up with to stay centered.
Context Anchor
Seen in airport diagrams, runway and taxiway markings, and PRM discussions about closely spaced parallel runways.
Why Pilots Care
Staying on centerline prevents runway excursions and ensures safe lateral separation between aircraft on closely spaced parallel runways during simultaneous operations.
Intuition Check
Centerlines do not always mean only the painted stripe you can see on the pavement. In runway-spacing discussions, they mean the lengthwise middle reference lines of the runways.
Example Sentence 1
After turning onto the runway, the pilot aligned the nosewheel with the centerline before advancing the throttle for takeoff.
Example Sentence 2
PRM alerts activate when an aircraft deviates from its assigned centerline toward the parallel runway.