Single-engine Class B - Landing — Page 327, Lesson 406

We've covered the regulation requirements for the maximum landing distance that must be available at a destination or alternate airfield. Now I want to walk you through how we actually calculate the gross landing distance when conditions aren't standard—specifically when we're dealing with grass runways, wet runways, and sloping runways. Let's start with grass. In CAP 698, Section 2, at the top of page 9 under point (b), we read that if the runway is grass up to 20 cm high, the landing distance should be multiplied by a factor of 1.15. That factor increases the landing distance by 15%. So if your calculated landing distance is, say, 1000 metres, on a grass runway up to 20 cm high you'd plan for 1150 metres. Next, wet runways. If there's an indication that the runway may be wet at the estimated time of arrival, the landing distance should again be multiplied by a factor of 1.15. Multiplying by 1.15 increases the landing distance by 15%. Now, here's an important point: if the aeroplane manual gives additional information on landing on wet runways, that information may be used even if it gives a lesser distance than the 1.15 factor from the paragraph above. So the manual's data can take precedence if it's more favourable. Now for slope. Point (d) in CAP 698, Section 2, page 9 states that no allowance is permitted for upslope. The reason is that an upslope will reduce the landing distance. If a pilot were to ignore that reduction, then a margin of safety would be incorporated into the landing distance calculation. So we don't credit the upslope benefit. However, the landing distance should be increased by 5% for each 1% downslope. That means for a 1% downslope, the landing distance is multiplied by a factor of 1.05. For a 2% downslope, the factor would be 1.1. Finally, point (e) states that there must be compliance with the despatch rules for scheduled or planned landing calculations, and these can be found in EU-OPS 1.550 (c). The despatch rules state that for despatching an aeroplane, it must be assumed that: first, the aeroplane will land on the most favourable runway at the destination airfield in still air; and second, the aeroplane will land on the runway most likely to be assigned, considering the probable wind speed and direction. If this second assumption cannot be met, the aeroplane may be despatched only if an alternate aerodrome is designated at which full compliance with the regulatory despatch requirements can be met. Let me clarify that first assumption. The most favourable runway, in still air or zero wind, means that assuming zero wind at the destination airfield, the runway which would accommodate the largest possible landing mass would be selected, since that is the most favourable runway. So we pick the runway that gives us the greatest landing mass capability under zero wind conditions.