What are centreline approach lights?
The long row of white lights laid along the extended runway centreline — the line a pilot follows out of the murk toward the threshold, long before the runway itself is visible.
Centreline approach lights are a row of lights on the extended runway centreline, running out from the threshold as the backbone of the approach lighting system. A precision system runs 900 m wherever possible, with lights every 30 m and the innermost light 30 m from the threshold. A simple system needs not less than 420 m, normally with lights every 60 m and the innermost light 60 m out — or 30 m and 30 m where better guidance is wanted.
In CAT I the lights are fixed white with variable intensity. Where barrettes are not used, each position has one light source in the first 300 m, two in the next 300 m and three in the outer 300 m — the distance-coded pattern. In CAT II/III the centreline over the first 300 m from the threshold consists of barrettes.
Frequently Asked Questions
Q1What are centreline approach lights?
They are the row of white lights laid along the extended runway centreline in an approach lighting system. They show the pilot where the runway centreline is while the runway itself is still hard to see, and the crossbars across them add roll and distance cues.
Q2How long is the centreline and how far apart are the lights?
A precision approach system runs the centreline over 900 m from the threshold wherever possible, with lights every 30 m and the innermost light 30 m from the threshold. A simple approach system needs not less than 420 m, normally with lights every 60 m and the innermost light 60 m from the threshold; a 30 m spacing, with the first light at 30 m, is used where better guidance is wanted.
Q3Why do some CAT I centrelines have one, two and then three lights per position?
Where barrettes are not used, a CAT I centreline has a single light source at each position in the innermost 300 m, two in the central 300 m and three in the outer 300 m. This is the distance-coded pattern: the number of lights per position tells the pilot roughly how far out from the threshold they are.
Q4What is a barrette and where is it used?
A barrette is a short row of closely spaced lights (three or more, in a line across the centreline) that reads as a single bar of light. CAT I centrelines may use barrettes instead of single light sources, and in a CAT II/III system the centreline over the first 300 m from the threshold consists of barrettes. Barrette systems are typically supplemented with sequenced flashing lights that flash toward the threshold.
Q5Are centreline approach lights the same as runway centreline lights?
No. Centreline approach lights are part of the approach lighting system and sit on the ground before the threshold, along the extended centreline. Runway centreline lights are inset in the runway surface and change colour toward the runway end. One system hands the pilot over to the other at the threshold.
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