Aerodromes - Visual Aids, Markings and Signs — Page 400, Lesson 538

Right, let's pick this up. We're moving into the visual aids part of the aerodrome chapter now, and I want to start with the signals area, because it's a neat little piece of infrastructure that tells you a lot about how an aerodrome operates. The signals area — sometimes called the 'signals square' — is a physical area on the ground. Its very presence at an aerodrome is a statement: it means that aerodrome accepts non-radio traffic. In other words, if you see a signals area, you know that aircraft without functioning radios, or pilots who simply aren't using radio, are permitted to operate there. That's the key implication of having one. Now, there's a condition attached. A signals area is not required if the aerodrome authority has proscribed routine non-radio traffic. 'Proscribed' means formally forbidden. So if the authority has banned routine non-radio operations, they don't need to provide the signals area. But — and this is an important but — the aerodrome would still be required to provide a service to an aircraft suffering a communications failure that has indicated the intention to land. So even a 'radio-only' aerodrome must still cater for an aircraft that has lost its radio but has signalled it wants to land. The signals area might not be there, but the service obligation remains. Let me give you the physical specifications, because these are the numbers you'll need. The signals area should be located so as to be visible for all angles of azimuth above an angle of 10° above the horizontal when viewed from a height of 300 m. Let me unpack that. 'Azimuth' is the full 360° circle around the horizon. So from a point 300 metres up — think of an aircraft on approach — the signals area must be visible in every direction around the compass, as long as you're looking at it at an angle greater than 10° above the horizontal. Below that 10° angle, it can be hidden by buildings or terrain; that's acceptable. Above it, it must be clear. The signals area itself shall be an even horizontal surface of at least 9 m square. So it's a flat, level patch of ground, and each side must be at least 9 metres long. The colour of the signal area should be chosen to contrast with the colours of the signal panels used. The panels are the actual signals that get displayed there, and you want the background to stand out against them so they're easy to read. And it should be surrounded by a white border not less than 0.3 m wide — so a white frame around the edge, at least 30 centimetres wide. It's normal for the signals area to be positioned in front — on the aerodrome side — of the control tower or VCR. VCR stands for Visual Control Room, which is the glass-fronted room in the tower where air traffic controllers actually look out at the aerodrome. So the signals area sits between the tower and the airfield, where the controller can see it and where pilots can see it from the air. The actual signals that may be displayed in the signals area — the panels themselves — are covered in Chapter 6, so we won't go into those here. Now let's move on to runway markings. First, the general principles. Markings are characters, numbers and shapes painted on the concrete surfaces of the aerodrome. They're found on runways, taxiways and aprons. Their purpose is to give location or directional information, or to indicate a mandatory requirement — for example, to stop. So a marking can tell you where you are, which way to go, or it can impose an order you must obey. The colour of a marking depends on where it's used, and the size must be sufficient for it to be read or understood easily from the flight deck of an aeroplane. That's the governing principle — it has to be legible from the cockpit. And here's the ICAO standard, which you should commit to memory: runway markings are white, and taxiway markings are yellow. That colour distinction is fundamental — white on the runway, yellow on the taxiway. Now, a practical detail about white runway markings. It's been found that on runway surfaces of light colour — concrete that's pale, for instance — the conspicuity of white markings can be improved by outlining them in black. 'Conspicuity' just means how noticeable they are. So you put a black outline around the white marking to make it stand out against a light background. There's also a friction consideration. Large areas of paint can create a friction problem on the runway surface — paint is smoother than the pavement. So this should be reduced, as far as practicable, by the use of a suitable kind of paint. The paint itself is chosen to minimise the slippery effect. Markings may consist of numbers and letters, solid areas, or a series of longitudinal stripes providing an effect equivalent to the solid areas. So instead of painting a big solid block, you can paint parallel stripes running along the runway that achieve the same visual effect but with less paint — which helps with the friction issue. Generally, runway markings assist the pilot with four things: locating the threshold, identifying the runway, defining the centre line, and locating the aiming point. Those are the core jobs. And additionally, for an instrument runway — a runway equipped for instrument approaches — as well as the aiming point, it will have touchdown zone markings. So the aiming point is there on all runways, but the touchdown zone markings are an extra feature specific to instrument runways. Let me show you what this looks like in practice. — that's the runway markings at RAF Brize Norton, and you can see the white markings laid out on the runway surface. Now, the runway designation marking. This is the marking that tells you which runway you're on. A runway designation marking is to be provided at the threshold of paved runways, and as far as is practicable at the threshold of unpaved — that is, grass — runways. So on a hard runway it's a requirement; on grass, you do it where you reasonably can. There's a special case here. If the runway threshold is displaced from the extremity of the runway — meaning the threshold, where landing is permitted to begin, is set back from the physical start of the runway surface — then a sign showing the designation of the runway may be provided for aeroplanes taking off. So for departing aircraft, who are starting at the extremity and rolling toward the displaced threshold, a sign can be placed to show them the runway designation. That's the take-off case. — that's the runway designation markings themselves, showing you the numbers as they appear on the threshold. So to tie it together: the signals area tells you about non-radio traffic and sits in front of the tower; runway markings are white, taxiway markings yellow; and the designation marking at the threshold identifies the runway, with a sign option for take-off when the threshold is displaced.