Runway centreline lights, every inset unit

Frequently Asked Questions

Why do centreline lights need their own inspection?

Because they fail differently from the rest of the runway lighting. They sit in the pavement where every aircraft rolls over them, so rubber, dust and de-icing residue build up on the lenses and the output drops a little at a time. A night walk sees which units are lit, not which ones are at half output. They are also the lights a crew relies on when visibility is lowest, and the rules give them their own limit, 95 percent serviceable for CAT II and III operations under ADR.OPS.C.015.

Does a dirty lens show up?

Yes, as a unit that reads low against its neighbours. Every unit on the centre line is measured from the same positions on the fly-over, so a lens under a film of rubber stands out from the clean units either side of it. The protocol names it with its figure and its position. What it cannot say is the cause. A low reading may be the lens, the lamp or water in the fitting, and telling them apart needs a hand on the unit.

Is the colour coding toward the runway end checked?

Unit by unit. Over the last part of the runway the centre line changes from white to alternating red and white and then to red, which tells a crew how much runway is left. Each unit's colour is read from the footage and set against the colour its position calls for. A white unit where a red one belongs, or a red filter that has faded, is reported at its position with the colour that was seen.

Is the runway closed for the inspection?

No. The fly-over is flown between aircraft movements in coordination with the tower, and the drone clears the runway when asked. A long runway is flown in more than one leg if the movements require it, and an interrupted leg is reflown unchanged rather than stitched. The lights have to be on at the intensity steps being checked, which is a request to your lighting control room rather than to the tower.

What about touchdown zone lights?

Where the runway has them, they are counted on the same fly-over, because the barrettes either side of the centre line are in frame on the same pass. They are reported as their own system with their own limit, 90 percent for CAT II and III operations under ADR.OPS.C.015, rather than added to the centre line count. They are scoped as a line item.

Can it be combined with the other runway lights?

That is the usual way to buy it. The centreline fly-over sits in the same sortie as the passes over the edge rows and the threshold and end bars, and the approach lights and the PAPI are measured from the approach in the same visit. Buying them together costs less than buying each separately, because the travel, the setup and the tower coordination are paid once.