Multi-engine Class B - Landing — Page 368, Lesson 445

All right, let's get into the landing performance side of a Multi-engine Class B aeroplane. We're going to look at how we calculate the gross landing distance, and the factors that the regulations force us to account for. The governing regulation here is CS-23. It tells us that when we calculate the gross landing distance, we must take certain details into account. So, let's walk through that list, because each item is a factor we have to build into our calculation. First, we have the pressure altitude at the aerodrome. That's the altitude corrected for the standard atmosphere's pressure, and it directly affects air density, which changes how the aeroplane performs. Next, we have standard temperature. We use the standard temperature for the calculation, not the actual temperature, unless the manual says otherwise. Then we have the runway surface conditions and the type of runway surface. This is where we start thinking about grass versus hard surfaces, and whether the runway is wet or dry. We also have the runway slope. That's the gradient of the runway, whether it's uphill or downhill. Now, here's a critical one: we must account for not more than 50% of the reported headwind component, or not less than 150% of the reported tailwind component. Let me unpack that. A headwind reduces your landing distance, so we only credit half of what's reported. That's a safety margin. A tailwind increases your landing distance, so we assume it's one and a half times worse than reported. That's a safety margin in the other direction. Finally, the despatch rules for scheduled or planned landing calculations, which are found in EU-OPS 1.550 (c). We'll come back to that in a moment. So, that's the regulatory framework. Now, let's look at the correction factors for non-standard conditions. These come from CAP 698, Section 3. We're talking about grass, wet, and slope. First, grass. If the runway is grass up to 20 cm high on firm soil, we multiply the landing distance by a factor of 1.15. That's a 15% increase. The grass creates rolling resistance and drag, so we need more distance to stop. Second, wet. If there's an indication the runway may be wet at the estimated time of arrival, we again multiply by 1.15, a 15% increase. Wet surfaces reduce braking effectiveness. But here's a nice provision: if the aeroplane manual gives additional information on wet runway landing, we may use that, even if it gives a lesser distance than the 1.15 factor. The manual's data is more specific to that aeroplane, so it can be more accurate. Third, slope. We increase the landing distance by 5% for each 1% downslope. So, a 1% downslope means we multiply by 1.05. A 2% downslope means we multiply by 1.1. A downslope makes you land downhill, which increases your ground speed and stopping distance. Now, point (d) also says no allowance is permitted for upslope. Why? Because an upslope reduces the landing distance. If we ignore that reduction, we're building in a margin of safety. We're being conservative, which is exactly what we want in performance calculations. Finally, the despatch rules. Point (e) says we must comply with the despatch rules for scheduled or planned landing calculations, and those are in EU-OPS 1.550 (c). This is the operational rule that governs whether an aeroplane can be despatched, meaning sent on a flight, based on the landing distance available at the destination and alternates. So, to tie it all together: we start with the gross landing distance, then we apply these correction factors for grass, wet, and slope, and we make sure we're compliant with the despatch rules. Each factor is a multiplier that increases the distance, except for the upslope, which we deliberately ignore to stay conservative. That's how we ensure the landing distance we plan for is safe and legal.