Aerodromes - Visual Aids, Markings and Signs — Page 400, Lesson 546

I want to walk you through the touchdown zone markings now — this is the second major runway marking we're covering, and it builds directly on the aiming point marking we just did. First, the definition. Touchdown zone markings — we abbreviate that TDZ — indicate the area of the runway where the aeroplane should be landed. That's their whole purpose. Now, here's an important operational point: Landing Distance Available, or LDA, is an operational consideration for the use of a runway, but it is not common practice to land the aeroplane on the threshold marking. In other words, the LDA tells you the runway length you can legally use for landing, but you don't actually aim to touch down right at the threshold. The TDZ markings give you, the pilot, an indication of the extent of the usable touchdown area, and if the markings are distance coded, they also tell you the length of the touchdown zone remaining. Now, where are these markings required? They are required for code 2, 3 and 4 paved precision approach runways. And they are recommended for code 3 or 4 paved non-precision or non-instrument runways, where additional conspicuity is required. So remember the contrast: required on precision approach runways for codes 2, 3, 4; recommended on non-precision or non-instrument runways for codes 3 or 4 when you need extra conspicuity. Let's look at the location. TDZ markings consist of pairs of rectangular markings symmetrically placed about the runway centre line. The number of pairs is related to the landing distance available. For code 4 runways — that's runways of 2400 metres or more in length — the TDZ markings have 6 pairs. Now the characteristics. Touchdown zone markings conform to either of two patterns. Pattern "A" is the basic marking system, whereas pattern "B" is distance coded. And note this: the choice of patterns is not runway length dependent. So you can't assume a longer runway gets one pattern and a shorter one gets the other — the choice is independent of length. The pairs of markings have longitudinal spacing of 150 metres, beginning from the threshold. And here's a nice interaction with the aiming point marking we just covered: if a pair of TDZ markings is coincident with, or located within 50 metres of, an aiming point marking, then the TDZ marking at that position is deleted from the pattern. So the aiming point marking takes priority, and you remove the conflicting TDZ pair. Let me tie this back to the aiming point location table we just saw, because they work together. The aiming point marking starts at a distance from the threshold that depends on the LDA — 150 metres for an LDA less than 800 metres, 250 metres for 800 up to but not including 1200, 300 metres for 1200 up to but not including 2400, and 400 metres for 2400 metres or more. And the TDZ pairs are spaced every 150 metres from the threshold. So you can see how a TDZ pair might land right on top of, or within 50 metres of, that aiming point marking — and in that case, the TDZ pair is deleted. So to summarise the whole picture: the aiming point marking tells you where to aim, the TDZ markings tell you the usable touchdown area, and the two are coordinated so they don't conflict. Pattern A is the basic plain marking, pattern B is distance coded, and the spacing between TDZ pairs is always 150 metres from the threshold.