Aerodromes - Visual Aids, Markings and Signs — Page 390, Lesson 535

I want to walk you through the visual aids, markings, and signs that make an aerodrome work for a pilot on the ground and in the circuit. This is a big subject, so let me start with the background and then get into the first set of visual aids. First, the background. The key idea here is standardization. No two aerodromes are the same — different layouts, different operations, different geographic positions. But the pilot taxiing an aircraft, or preparing for landing or take-off, needs consistent visual information everywhere. That's why Annex 14 to the Chicago Convention specifies the SARPs — that's Standards and Recommended Practices — for these visual aids. And I want you to note something important: while all Contracting States adopt these SARPs, there can be differences. You might see signs at a foreign aerodrome that you wouldn't see on a UK aerodrome, and vice versa. So the standard is the baseline, but don't assume universal uniformity. The subject is broken into three sections: visual aids for navigation, aerodrome markings, and aerodrome signage. Let's start with the first — visual aids for navigation. The first thing an aerodrome must have is a means of indicating wind direction to pilots of non-radio aircraft. Think about why. The Rules of the Air require a pilot to land and take off into wind. So if you're flying an aircraft without radio, you need a way to know which way the wind is blowing, and therefore which runway direction to use. That's where the wind direction indicator comes in. There's also a landing indicator — this tells the non-radio pilot what the landing direction actually is. And there's a requirement for a means of communicating visual signals to non-radio aircraft, and that must be positioned in the visual control room. So the aerodrome has to be able to signal you visually, not just by radio. Now, the wind direction indicator itself — commonly called a wind sock. The aerodrome must have at least one. And here's the construction detail you need to know. It should be in the form of a truncated cone made of fabric. A truncated cone means a cone with the point cut off, so it's open at both ends — the larger end catches the wind, and the smaller end trails away. The length must be not less than 3.6 metres, and the diameter at the larger end — well, the excerpt cuts off there, but that's the specification we're building from. So the wind sock is your primary visual cue for wind direction and, by how it streams, an indication of wind strength. For a non-radio pilot, that's your first piece of information before you even think about the landing direction indicator. Let me pause there. We've covered the background on standardization and SARPs, the three-section breakdown, and the first visual aids — the wind direction indicator, the landing indicator, and the visual signalling from the control room. When you're ready, we'll move into the next part of the visual aids for navigation.