How does rubber deposit build up on inset lights?
Every landing lays a little tyre rubber on the touchdown zone, and inset lights sit right in the wheel path. Pick a condition to see what the deposit does to the beam, and what cleaning restores.
The full beam leaves the prism at the shallow angles the pilot needs, and output matches the photometric design.
Treat this as the reference when judging a deposit. Plan cleaning in touchdown areas before output is visibly reduced.
When an aircraft touches down, its tyres spin up and leave rubber on the pavement. Inset lights in the touchdown zone sit in that wheel path, so the rubber settles on their optical window too, layer after layer, landing after landing.
Because the beam leaves at shallow angles along the runway, even a thin dark film absorbs and scatters a large share of it. The light can still look lit from above while delivering far less intensity to the pilot, and a thick deposit can block it almost completely. Annex 14 treats an inset light as unserviceable once its main-beam average intensity falls below 50% of the specified value, and a heavy deposit can take it well below that.
Cleaning restores output, but only with an approved method. Harsh or abrasive removal can scratch the prism or loosen the fixture and leave the light worse than before.
Wheel paths and concentrated landings lay deposit fastest, so these lights need the most frequent checks and cleaning.
Much less rubber reaches these lights, so deposit builds slowly and cleaning is needed less often.
Frequently Asked Questions
Q1Why do inset lights collect rubber?
Aircraft tyres lay down rubber as they touch down and spin up. Inset lights sit in the pavement along that wheel path, so deposit settles on the optical window as well as on the surrounding surface.
Q2Does a light with rubber on it still look lit?
Usually yes. From above the source can still glow, but the film absorbs and scatters the low beam, so much less intensity reaches the pilot along the runway.
Q3Which lights are most affected?
Lights in the touchdown zone and under common wheel paths, where landings are concentrated. How fast deposit builds depends on traffic volume and aircraft types.
Q4How is rubber removed from inset lights?
By methods the site and the manufacturer approve, such as high-pressure water or purpose-built rubber-removal equipment. Abrasive or harsh methods can scratch the prism or damage the fixture.
Q5Can cleaning damage an inset light?
Yes. A scratched or chipped window, a loosened fixture or a damaged seal can cost more output than the rubber did, so use the approved method and respect the manufacturer's limits.
Q6What should be checked after cleaning?
That the window is clear and undamaged, that the fixture is still seated and not raised, that seals and bolts are sound, and that the light operates. Record the clean.
Q7When is a light with rubber on it counted as unserviceable?
Under ICAO Annex 14, an inset light is deemed unserviceable when its main-beam average intensity falls below 50 per cent of the value specified for it. A glowing window proves nothing, so the check is a photometric measurement, which is why touchdown-zone lights are measured and cleaned on a schedule rather than judged by eye.
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