Right, let's pick this up — Page 411, Lesson 565

Right, let's pick this up. We've covered the blue taxiway edge lights and the fact that the edge markers themselves must be frangible — that means they're designed to break away easily if an aircraft hits them, so they don't damage the aircraft. Now I want to walk you through the next three types of markers, because each one has a very specific job and a very specific colour or shape. First, 20.50 — Taxiway Centre Line Markers. These are your fallback. They should be provided on a taxiway where edge lights or taxiway edge markers are not provided. So if you've got neither of those edge systems, you put centre line markers down instead. Now, the positioning is precise. The markers should be installed at least at the same location as taxiway centre line lights would have been, had they been used. In other words, they sit where the centre line lights would sit. Normally, they're located right on the taxiway centre line marking — that's the painted line on the pavement. But there's a tolerance: they may be offset by not more than 30 cm where it's not practicable to locate them on the marking. So if something physically prevents you putting the marker exactly on the line, you can shift it sideways, but never more than 30 centimetres. Now the colour — and this is a key one for you. Taxiway centre line markers are reflective green. Not blue, not white — green, and reflective, so they shine back at you when your landing light hits them at night. And there's a structural requirement that matters for safety: the markers shall be so designed and fitted to withstand being run over by the wheels of an aircraft without damage either to the aircraft or to the markers themselves. So they're not just fragile sticks — they have to survive a nosewheel or mainwheel rolling right over them, and they must not damage the tyre or the aircraft in the process. Next, 20.51 — Unpaved Taxiway Edge Markers. This is for taxiways that aren't paved, so the surface is grass or dirt. The rule is: where the extent of an unpaved taxiway is not clearly indicated by its appearance compared with that of the surrounding ground, markers should be provided. So if the taxiway blends into the grass and you can't tell where it ends, you need markers to define it. Now there are two cases. Where taxiway lights are provided, the markers should be incorporated in the light fixtures — so the marker is built into the light unit itself. Where there are no lights, markers of conical shape should be placed so as to delimit the taxiway clearly. So no lights — you use cone-shaped markers, and their job is to clearly mark the boundary of the taxiway. Finally, 20.52 — Stopway Edge Markers. A stopway is that area beyond the runway end, and its edge markers have one critical requirement: they shall be sufficiently different from any runway marker used to ensure that the two types cannot be confused. So the whole point is discrimination — you must never mistake a stopway edge marker for a runway marker, because that could mislead you about where the runway actually ends. And there's a note here, an operational note: markers consisting of small vertical boards camouflaged on the reverse side, as viewed from the runway, have proved operationally acceptable. So the accepted design is a small vertical board, and the side facing the runway is camouflaged — painted or coloured to blend in — so that when you're looking at it from the runway, it doesn't stand out and get confused with runway markings. It only clearly reads as a stopway marker from the other side. So to tie it together: centre line markers are green, reflective, sit on or within 30 cm of the centre line, and must survive being run over. Unpaved taxiway edge markers are either built into light fixtures or are cones, and they exist only when the taxiway edge isn't obvious. And stopway edge markers must be visually distinct from runway markers, with the camouflaged board being the proven acceptable solution.