Single-engine Class B - Landing — Page 327, Lesson 404

Let’s pick this up right where the calculation left off. We had a gross landing distance of 1200 ft, and we multiplied it by 1.43 to get 1716 ft. That 1716 ft is the net landing distance — the one-in-a-million worst-case scenario. So the regulation says: the landing distance available at your destination must be at least 1716 ft. If the runway is longer than that, the aeroplane can land within 70% of the landing distance available, and you satisfy the rule. Now, why 1.43? Because 1 divided by 0.7 equals 1.43. The regulation requires the landing distance to be no more than 70% of the landing distance available. So to find the minimum runway length, you take the gross landing distance and divide by 0.7 — which is the same as multiplying by 1.43. That’s the whole point of Figure 10.2: multiply the gross landing distance by 1.43 to get the minimum runway length required. This is where the difference between net and gross performance becomes clear. The gross performance is the 1200 ft — the distance the aeroplane actually needs under test conditions. The net performance is 1716 ft — always worse than gross, and it’s the one-in-a-million worst-case scenario. So the regulation builds in that safety margin. Now, where does this rule live? It’s in CAP 698, Section 2, at the top of page 9. The regulation states that the landing distance, measured from a screen height of 50 ft, must not exceed 70% of the landing distance available. The screen height of 50 ft is the height at which the aeroplane crosses the threshold — the start of the runway — during the approach. So the landing distance is measured from that 50 ft point to the point where the aeroplane comes to a full stop. If the aeroplane cannot stop within that 70% length, you have two options to reduce the landing distance: either select a higher flap setting, or reduce the mass of the aeroplane. Higher flaps increase drag and lower the approach speed, so the aeroplane stops sooner. Reducing mass means less kinetic energy to dissipate, so it also stops sooner. Now, the factors that must be accounted for when calculating the gross landing distance — these come from CS-23. Let me walk you through each one, because each affects the distance in a specific way. First, the pressure altitude at the aerodrome. Higher pressure altitude means thinner air, so the aeroplane lands at a higher true airspeed, and the landing distance increases. Second, standard temperature. The calculation assumes standard temperature conditions. If the temperature is higher than standard, the air is less dense, and again the landing distance increases. Third, the runway surface conditions and the type of runway surface. A wet, icy, or grass runway has less friction, so the braking effectiveness is reduced, and the landing distance increases. The type of surface — whether it’s asphalt, concrete, or grass — also affects the friction. Fourth, the runway slope. A downhill slope — a negative slope — increases the landing distance because the aeroplane has a component of gravity pulling it forward. An uphill slope decreases the landing distance. Fifth, and this is a critical one: not more than 50% of the reported headwind component, or not less than 150% of the reported tailwind component. A headwind reduces the groundspeed, so it reduces the landing distance — but you can only credit 50% of the reported headwind. A tailwind increases the groundspeed, so it increases the landing distance — and you must assume at least 150% of the reported tailwind. This is a safety factor: you can’t rely on the full headwind, but you must assume more tailwind than reported. Finally, the despatch rules for scheduled or planned landing calculations — that’s EU-OPS 1.550 (c). This refers to the operational rules that govern how you plan the landing for a scheduled flight. It ties the performance calculation into the regulatory framework for dispatch. So, to summarise the whole picture: you start with the gross landing distance, you multiply by 1.43 to get the net landing distance, and that net distance must fit within 70% of the landing distance available. The factors from CS-23 — pressure altitude, standard temperature, runway surface and type, runway slope, the headwind/tailwind limits, and the EU-OPS despatch rules — all feed into that gross landing distance calculation. If the net distance doesn’t fit, you increase flap or reduce mass. That’s the complete landing performance story for a single-engine Class B aeroplane.