What are the longitudinal and lateral dimensions of approach lighting?
How far the pattern runs along the centreline, how far apart the lights sit, and how wide the crossbars and side rows reach.
Approach light dimensions come in two directions. Longitudinal dimensions run along the extended runway centreline, measured outward from the threshold: the length of the system, the spacing between lights and the position of each crossbar. Lateral dimensions run across the centreline: the width of a crossbar and the sideways position of the side rows.
On a precision runway the ICAO centreline is 900 m long wherever possible, with lights 30 m apart and the innermost light 30 m from the threshold. A simple system needs at least 420 m, normally with lights 60 m apart. The pattern is symmetrical about the axis, and the lowest-visibility layout is the most closely packed.
Length from the threshold, light pitch, and crossbar positions at 150 m and 300 m. In CAT II/III the red side rows end at 270 m (240 m is allowed where the serviceability objectives can be demonstrated).
Crossbar width: 30 m in CAT I (18 m or 30 m in a simple system). Side rows sit either side, innermost lights at the touchdown zone light spacing.
| System | Length | Longitudinal spacing | Crossbars | Lateral features |
|---|---|---|---|---|
| Simple (ICAO) | at least 420 m | 60 m (30 m for better guidance) | One, 18 m or 30 m wide, at 300 m | Centreline and crossbar only |
| CAT I (ICAO) | 900 m wherever possible | 30 m; first light 30 m from threshold | One, 30 m wide, at 300 m (extra bars at 150, 450, 600, 750 m optional) | Centreline and crossbar only |
| CAT II / III (ICAO) | 900 m wherever possible | 30 m; barrettes in the inner 300 m | Two, at 150 m and 300 m | Red side rows to 270 m, 30 m pitch, innermost lights at the touchdown zone light spacing |
| FAA MALSR | 2,400 ft | Bars every 200 ft out to 1,400 ft; RAIL flashers every 200 ft | 1,000-ft bar, about 66 ft wide | None |
| FAA ALSF-2 | 2,400 ft (3,000 ft at some sites) | Barrettes every 100 ft | 1,000-ft bar about 100 ft wide, plus a 500-ft bar | Red side rows, 3 lights per bar, 100 to 900 ft |
Scroll sideways on a small screen. ICAO rows are metric; FAA rows are in feet and differ in detail.
Frequently Asked Questions
Q1What are the longitudinal dimensions of approach lighting?
They are the distances measured along the extended runway centreline from the threshold: the length of the system, the spacing between lights, and the positions of the crossbars and side rows. For a precision approach the ICAO system is 900 m long wherever possible, with lights 30 m apart and the first light 30 m from the threshold. A simple system is at least 420 m long, normally with lights 60 m apart.
Q2What are the lateral dimensions of approach lighting?
They are the sideways dimensions across the centreline: how wide each crossbar is and how far the side rows sit from the centreline. The pattern is symmetrical about the extended axis. A CAT I crossbar is 30 m wide at 300 m; a simple system uses an 18 m or 30 m crossbar at the same position. In CAT II and III the red side rows sit either side of the centreline, with their innermost lights at the same lateral spacing as the touchdown zone lights.
Q3Where is the datum for approach light dimensions?
The runway threshold. Every distance is measured outward from the threshold along the extended centreline, so a crossbar "at 300 m" is 300 m before the threshold. This is why the pattern reads the same way at every runway end.
Q4How do the dimensions change between CAT I and CAT II/III?
The 900 m length, the 30 m spacing and the 300 m crossbar stay the same. CAT II and III add two red side rows out to 270 m (240 m where the maintenance serviceability objectives are shown to be met), a second crossbar at 150 m, and barrettes in the inner 300 m of the centreline. These additions give roll and distance-to-go cues when only a short length of the pattern can be seen.
Q5Are FAA approach lighting dimensions the same as ICAO?
No. FAA systems are in feet and differ in detail. MALSR is 2,400 ft long, with bars every 200 ft out to 1,400 ft and a crossbar about 66 ft wide at 1,000 ft. ALSF-2 is 2,400 ft long, with barrettes every 100 ft, a 1,000-ft bar about 100 ft wide, a 500-ft bar and red side rows over the inner 900 ft.
Q6Where are approach lighting dimensions defined?
In ICAO Annex 14 Volume I (Chapter 5, approach lighting systems) and the Aerodrome Design Manual Part 4, and for FAA-regulated airports in FAA AC 150/5340-30 and FAA Order 6850.2. The project specification and the standard in force for the runway govern, so always confirm the figures in the current edition.
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