How is an approach lighting system selected?
Four decisions, taken in order, that narrow the choice to the right approach lighting system for a runway end.
Approach lights lead the pilot in toward the threshold, so the system is chosen for the approach the runway supports. The approach type sets the length and spacing, the category sets the centreline pattern and crossbars, the fixture mounting decides how each light is held, and the site and control decide the structure and the intensity steps.
The flowchart only narrows the choice. The final system is confirmed against the design for length, spacing and crossbars, fixtures and aiming, frangible structures and intensity control, and against the standard in force for the runway.
Frequently Asked Questions
Q1How is an approach lighting system selected?
By working through a few decisions in order: what type of approach the runway supports, which precision category applies, how the lights are mounted, and what ground and control the system must suit. The result is then checked against the design, the standard and the manufacturer’s data.
Q2What is the difference between simple and precision approach lighting?
A simple system extends at least 420 m from the threshold, normally with centreline lights every 60 m and one crossbar at 300 m. A precision system for CAT I, II and III extends 900 m wherever possible, with centreline lights every 30 m. The type of approach the runway supports decides which is provided.
Q3How does the category change the system?
In CAT I the centreline lights are fixed white with variable intensity, either distance-coded with three, two and one light sources in successive 300 m stretches moving out from the threshold, or barrettes. In CAT II and III the centreline over the first 300 m consists of barrettes, and crossbars are provided at 300 m and 150 m. Two red side rows of barrettes also run along the inner 270 m (240 m where the required serviceability is demonstrated).
Q4Why are approach lights frangible?
An aircraft that lands short could strike them, so every elevated light and its support must yield on impact. In the inner 300 m the whole structure is frangible. Beyond that, where a support is taller than 12 m, only the top 12 m must be, and the mass of the light and structure is kept as low as possible.
Q5What should be checked before the choice is final?
That the length, spacing and crossbars match the category, that the fixtures and their aiming suit the design, that the structures are frangible and hold the lights in the plane through the threshold, and that the intensity steps and regulator suit the control system. The standard in force and the manufacturer’s data decide.
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