Definition
A system of flush-mounted lights installed along the centerline of a runway to provide visual guidance during takeoff, landing, and rollout in low-visibility conditions. The lights are spaced at regular intervals along the full length of the runway and change color near the departure end to warn pilots of remaining runway distance: white for most of the runway, alternating red and white for the next-to-last 3,000 feet, and steady red for the final 1,000 feet.
Plain English
A line of lights set into the surface of the runway, running right down the middle, that helps pilots stay aligned during takeoff and landing when visibility is poor. The lights also change color as you near the end of the runway so you know how much room you have left.
Context Anchor
You see this system while landing, taking off, or rolling on a lighted runway, especially at larger airports or in low-visibility conditions.
Why Pilots Care
Keeps the aircraft centered on the runway surface, lowering the chance of drifting off the edges especially when visibility is poor.
Analogy
It is like a lighted path down the middle of the runway, giving the pilot a clear line to follow when the edges or surroundings are hard to see.
Intuition Check
Do not confuse the Runway Centerline Lighting System with the painted centerline stripe. The stripe is paint; this system is actual runway lighting installed along that centerline.
Example Sentence 1
With visibility down to half a mile, the captain relied on the runway centerline lighting system to stay aligned during the landing rollout.
Example Sentence 2
In low visibility, the crew tracked the runway centerline lighting system from touchdown to the turnoff point.