High-Intensity Runway Centreline Light

A High-Intensity Runway Centreline Light is a flush-mounted inset light installed along the exact centre of the runway, designed specifically for CAT II and CAT III precision approach operations. These lights provide the same longitudinal guidance as standard centreline lights but with a significantly higher luminous intensity (typically 2x to 3x higher) to ensure visibility in very low visibility conditions (RVR as low as 75 metres for CAT IIIB). The colour coding is identical: white lights from the threshold to 900 metres from the runway end, alternating red and white from 900 to 300 metres, and all red from 300 metres to the runway end. This colour transition gives pilots a visual cue of the remaining runway length, even in the most challenging weather conditions.

This fixture exists to solve a specific problem: at RVR 75 m, the slant visual range available to a pilot on the runway is barely longer than the aircraft itself, so any light that isn't intense enough simply won't be seen in time to be useful. The higher luminous output is not a general upgrade for its own sake — it is what keeps the centreline visible at the exact distance and contrast level a CAT IIIB landing or rollout demands, when a standard centreline light would already have fallen below what the eye can pick out through fog. The white-to-red colour transition then carries the added burden of telling the pilot how much runway remains using colour alone, since at that visibility there is effectively no other way to judge remaining distance visually. In this way the fixture's purpose is inseparable from the specific low-visibility regime it is built for: it is the difference between centreline guidance that works down to CAT I minima and guidance that continues to work when there is almost nothing else to see by.

Installed exclusively on CAT II and CAT III precision approach runways where low-visibility operations are conducted. The lights are spaced at approximately 15-metre (50 ft) intervals, the ICAO/FAA centreline spacing for CAT II/III (30 m is accepted on lower-category runways), giving the dense visual cue pattern low-visibility guidance needs. They are used in conjunction with high-intensity runway edge lights, touchdown zone lights, and approach lighting systems (ALSF-2) to provide comprehensive visual guidance during all phases of the approach and landing in RVR conditions down to 75 metres (CAT IIIB).

Fixtures are recessed into the runway pavement along the centreline at the 15 m (50 ft) spacing required for CAT II/III operations, using a load-rated inset base can set flush with the surface to withstand full aircraft wheel loads at the runway's declared load classification. Because these fixtures sit on the primary runway surface, setting-out is tied directly to the runway centreline survey used for the associated ALSF-2 and touchdown zone lighting, with base can position checked against pavement joints and the runway's grooving/friction-course pattern so the fixture doesn't compromise surface drainage; cabling runs in duct beneath the pavement back to isolating transformers on the runway centreline series circuit.

Each high-intensity centreline light is powered from the constant current series circuit via an isolating transformer. The lights use a bi-directional optical system with high-output LEDs or halogen lamps to project a narrow, high-intensity beam (typically 4° vertical x 6° horizontal) both ahead and behind the fixture, ensuring visibility to pilots on approach and during roll-out. The colour transition is achieved using precision dichroic filters or coloured lenses. The intensity is controlled by the CCR's current steps, with the highest intensity step (6.6A) delivering up to 20,000 cd or more to ensure visibility in the lowest RVR conditions. The fixtures are designed with advanced thermal management to handle the higher power dissipation of high-intensity operation.

High-intensity centreline lights are not individually addressable — control is exercised at the loop level through the constant current series circuit, which on precision approach runways is typically sectionalised so the ALCMS can command different current steps (or switch sections off entirely) as an aircraft progresses down the runway during roll-out, rather than running the full centreline row at one fixed setting throughout. The ALCMS, driven by tower instruction or an automated RVR-linked routine, selects the required brightness step for each active section; this command passes to the CCR, which regulates that section of the loop to the corresponding fixed current, up to 6.6A for the lowest RVR conditions the fixture is rated to serve. Every fixture within an active section, via its own isolating transformer, draws the same current and burns at the same intensity simultaneously — the colour transition along the centreline (white, alternating red/white, solid red) is fixed by each fixture's dichroic filtering at installation, not by anything the CCR commands, so loop-level current control and the fixed colour-zone layout operate independently of one another. Fault detection remains loop-based: the CCR monitors loop voltage against commanded current, and a voltage rise — typically an open-circuit lamp or failed isolating transformer — is reported to the ALCMS as a loop fault pending sectionalised field testing to isolate the exact fixture.

The fixture is a die-cast aluminium housing set flush into an L-868 base can rated for 100,000kg wheel loading, with a bi-directional lens assembly — one high-output LED array or 100W halogen lamp viewed through separately masked white, red/white, and red zones depending on the fixture's position along the runway. The lens is glass or high-strength polycarbonate, gasket-sealed to the housing for an IP67/IP68 submersible, pressure-vented rating that copes with the hydraulic loading of aircraft tyres passing directly overhead. Internal wiring runs to an L-823 primary connector mating to the isolating transformer's secondary leads in its own base can, with stainless-steel fasteners and a drainage provision preventing water pooling at the cable entries — the same base-can construction as the standard high-intensity runway light, just built to the higher output and pressure-venting spec that CAT II/III precision runways require.