Definition
A painted line running down the middle of a runway, taxiway, or road used as a visual reference to keep the airplane tracking straight along the surface or, when used as a ground feature during flight training, to provide a straight line over the ground for practicing straight-and-level flight.
Plain English
A painted line down the middle of a runway, taxiway, or road that a pilot uses as a straight line to fly along or taxi along.
Context Anchor
Seen when using outside visual references during basic flight training, and also on runways and taxiways while operating on the ground or near an airport.
Why Pilots Care
Maintaining alignment with the marked centerline prevents runway excursions and loss of directional control.
Intuition Check
Do not read “marked” as simply “noticeable.” Here it means the centerline is intentionally shown by paint, markings, or another clear visual guide. Do not assume the airplane’s nose always points exactly along the marked centerline; wind can make the airplane point slightly one way while it moves along another path.
Example Sentence 1
The instructor told the student to pick a long, marked centerline on the highway below and fly straight along it to practice holding heading.
Example Sentence 2
On final approach the pilot aligns the aircraft with the marked centerline to ensure a centered touchdown.