Let’s pick this up right where the numbers matter most — Page 400, Lesson 542

Let’s pick this up right where the numbers matter most. I want to walk you through the runway threshold marking, because this is one of those items examiners love and pilots must read at a glance. First, the stripe-and-gap rule that opens this passage. On a runway, the threshold stripes are painted as a series of longitudinal stripes with gaps between them. The rule is that the length of one stripe plus one gap — that combined distance — shall be not less than 50 metres and not more than 75 metres. So you have a window: 50 to 75 metres for the stripe-plus-gap unit. And within that, each stripe itself must be at least equal to the length of the gap, or 30 metres, whichever is greater. So if the gap is 40 metres, the stripe must be at least 40 metres. If the gap is only 20 metres, the stripe must still be at least 30 metres, because 30 is the floor. Now, what is the threshold itself? The threshold of a runway is either the beginning of the marked-out grass area, or the start of the concrete strip. That’s the definition — the point where the usable runway surface begins. When is a threshold marking required? It is required at the thresholds of paved instrument runways, and of paved non-instrument code 3 and 4 runways, provided the runway is intended for use by international commercial air transport. So the requirement attaches to paved instrument runways, and to the larger paved non-instrument runways — code 3 and 4 — when they serve international commercial air transport. For an unpaved runway, a threshold marking should be provided as far as is practicable — that’s a recommendation, not a hard requirement. Now the location. The stripes of the threshold marking — commonly known as the “piano keys” — should start 6 metres from the threshold. So you measure 6 metres back from the threshold line, and that’s where the stripes begin. Let’s look at the characteristics, because this is where the geometry gets precise. A runway threshold marking is a pattern of longitudinal stripes of uniform dimensions, disposed symmetrically about the centre line of the runway. So the stripes run along the runway length, all the same size, and they’re mirrored about the centre line. For a runway width of 45 metres — and note, for non-precision approach and non-instrument runways, that’s 45 metres or greater in width — the stripes may be placed either side of the runway designation number. The stripes should extend laterally to within 3 metres of the edge of the runway, or to a distance of 27 metres on either side of the runway centre line, whichever results in the smaller lateral distance. So you compute both limits — 3 metres from the edge, or 27 metres from the centre line — and you take whichever gives the smaller distance from the centre line. That keeps the stripes inside the usable surface. Now the interaction with the runway designation marking — that’s the big number painted at the threshold, like “27” or “09”. There are two ways it can sit relative to the threshold stripes. If the designation marking is placed within the threshold marking, there will be a minimum of three stripes on each side of the centre line of the runway. If the designation marking is placed above the threshold marking, then the stripes shall be continued across the runway — meaning the stripes run right through, underneath the designation. The stripes themselves shall be at least 30 metres long, and approximately 1.80 metres between them — that’s the gap between adjacent stripes. But there’s an exception: where the stripes are continued across a runway, a double spacing shall be used to separate the two stripes nearest the centre line of the runway. So in that continued-across case, the two stripes closest to the centre line get a wider gap — double the normal spacing. And in the case where the designation marking is included within the threshold marking, that spacing — the gap between those two centre-line stripes — shall be 22.5 metres. So you have a specific number: 22.5 metres for that centre gap when the designation sits within the threshold marking. Finally, the number of stripes shall be in accordance with the runway width — and that’s the table that follows this passage, which we’ll take next. I’ve got the figures here that show you exactly what this looks like in practice — the runway markings at RAF Brize Norton, and the runway designation markings. Let me bring those up for you. So the key numbers to hold onto: stripe-plus-gap between 50 and 75 metres; stripe at least 30 metres or equal to the gap, whichever is greater; stripes start 6 metres from the threshold; stripes extend to within 3 metres of the edge or 27 metres from the centre line, whichever is smaller; stripes at least 30 metres long; approximately 1.80 metres between stripes; double spacing at the centre when stripes continue across; and 22.5 metres for that centre gap when the designation is within the threshold marking.