What is a crossbar in approach lighting?
A horizontal line of white light laid across the approach path — the lateral bar that tells a pilot where the extended runway centreline is, how level the aircraft is, and how far out from the threshold they are.
A crossbar is a row of lights perpendicular to the extended runway centreline, forming part of the approach lighting system. In a CAT I system a single 30 m crossbar sits 300 m from the threshold; a simple system uses an 18 m or 30 m crossbar at the same 300 m position; and a CAT II/III system has two crossbars, at 150 m and 300 m.
The crossbar lights are fixed white lights of variable intensity, just like the centreline they cross. Together they give the pilot a roll (bank) and lateral reference, and because every crossbar sits at a known distance from the threshold, they also help judge how far there is to run. In a CAT I system whose centreline uses single light sources, additional crossbars may be provided at 150, 450, 600 and 750 m, giving the five-crossbar pattern of the Calvert system.
Precision Approach Category Lighting
For precision approach, the crossbar arrangement follows the category. A CAT I system has a 900 m centreline with one 30 m crossbar at 300 m from the threshold; extra crossbars are an option, not a requirement. A CAT II/III system has crossbars at 150 m and 300 m, with red side rows over the inner 270 m. The lights are fixed white lights of variable intensity.
Non Precision Approach Lighting
A non-precision approach is served by a simple approach lighting system: a centreline of at least 420 m with one 18 m or 30 m crossbar at 300 m from the threshold. The crossbar gives the pilot a roll and lateral reference and marks a fixed distance from the threshold.
Frequently Asked Questions
Q1What is a crossbar in an approach lighting system?
A crossbar is a row of lights laid perpendicular to the extended runway centreline, forming a horizontal line of white light across the approach. It gives the pilot a roll and lateral reference and marks a fixed distance from the threshold.
Q2Where is the crossbar placed?
In a simple approach lighting system and in a precision approach CAT I system, a crossbar sits 300 m from the threshold. A CAT II/III system has two crossbars, one at 150 m and one at 300 m from the threshold.
Q3How long is the crossbar?
The CAT I crossbar at 300 m is 30 m in length. A simple approach lighting system may use an 18 m or a 30 m crossbar at the same 300 m position.
Q4What colour and type of light does a crossbar use?
In a CAT I system the centreline and crossbar lights are fixed white lights with variable intensity. The side rows used in CAT II/III are red, but the crossbars stay white.
Q5Why does a CAT II/III system have a second crossbar at 150 m?
The inner 300 m is where the lowest-visibility approaches rely most on visual cues. The second crossbar at 150 m gives an extra roll reference and a second known distance mark there, in addition to the 300 m bar.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.