Class A - Landing — Page 478, Lesson 588

Let's start with the landing distance requirements, because that's the heart of Class A landing performance. The rule comes from EU-OPS 1.515, and it's a hard limit on how much runway you're allowed to need. The landing distance required — that's the distance the aeroplane actually needs to land — is measured from 50 feet above the runway threshold to a full stop. And that required distance must not exceed a certain percentage of the landing distance available, which is the runway length you actually have to work with. Here's the key split: for a turbojet aeroplane, the required landing distance must not exceed 60% of the landing distance available. For a turboprop aeroplane, it's 70%. So if you're flying a jet, you need at least 1.67 times the required distance available; if you're on a turboprop, you need at least about 1.43 times. That's the safety margin built into the regulation. Now, there's a note about short landing and steep approach procedures. Those may be approved based on lower screen heights — the screen height is the height above the threshold at which you cross it — but not less than 35 feet. So the standard is 50 feet, but with special approval you can go down to 35 feet minimum. Let me be precise about what the landing distance required is based on, because each of these factors matters. First, the aeroplane must be in the landing configuration — that means gear down, flaps in the landing setting. Second, the speed at 50 feet must not be less than 1.23 times VSR0, or VMCL. Let me define those two speeds carefully, because they're critical. VSR0 is the stall reference speed in the landing configuration. That's the reference stall speed with the landing configuration set. The 1.23 factor means you must be flying at least 23% faster than that reference stall speed when you cross the 50-foot point. VMCL is the minimum control speed during approach and landing with all engines operating. It's defined as the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is still possible to maintain control of the aeroplane with that engine inoperative, and maintain straight flight with an angle of bank of not more than 5° towards the live engines. So if one engine fails on approach, you must be able to keep the aircraft straight and level — well, straight, with a small bank of no more than 5° toward the good engines — and that defines the minimum speed you can use. The landing distance required is also based on the aerodrome pressure altitude — that's the altitude corrected for the actual pressure at the field. It's based on standard day temperature, which is ISA — International Standard Atmosphere. It's based on factored winds: 50% of the headwind is counted, and 150% of the tailwind is counted. So a headwind helps you, but only half of it is credited; a tailwind hurts you, and it's penalised by counting 150% of it. And finally, the runway slope is considered if it's greater than plus or minus 2%. Now let's move to runway selection and despatch rules. This is about choosing which runway to plan for. You must consider landing both in still air and in the forecast wind. In still air, you may select the most favourable runway — the one that gives you the longest effective landing distance. In forecast wind, you must consider the runway most likely to be used in that forecast wind. Then you take the lower of the two masses obtained from these two cases — the still air case and the forecast wind case — and that lower mass becomes the limiting mass for the field lengths available. So you plan for the worst of the two scenarios. Now, non-compliance. There are two situations. First, if the still air requirement cannot be met at an aerodrome with a single runway — meaning you can only land if there's an adequate wind component — then the aircraft may still be despatched, but only if 2 alternate aerodromes are designated at which full compliance is possible. So you need two alternates that fully meet the landing requirements. Second, if the forecast wind requirement cannot be met, the aeroplane may be despatched if an alternate is designated at which all the landing requirements are met. So one alternate suffices in that case. Now, wet runways. If the runway is forecast to be wet at the estimated time of arrival, then the landing distance available must be at least 115% of the required landing distance. So you need 15% more runway available than required. However, a lesser factor may be used, so long as it is published in the aeroplane flight manual and the authority has approved such a factor. So the 115% is the default, but a smaller factor is possible if it's documented and approved. Finally, the presentation of data. The example graph in Figure 18.2 can be found in CAP 698, on page 46 of section 4. You should work through the example shown in the graph, which is detailed on page 40 of section 4. Practise using the questions at the end of the chapter, and remember you'll need to work through these graphs both in the normal way — as illustrated by the arrow heads in the example — but also in reverse. So you need to be able to read the graph forward, finding the landing distance for a given mass, and also backward, finding the limiting mass for a given runway length. That's the core of Class A landing performance. The key numbers to hold onto: 60% for jets, 70% for turboprops, 50-foot screen height, 1.23 times VSR0, the VMCL definition, the wind factoring of 50% headwind and 150% tailwind, the 2% slope threshold, and the 115% wet runway factor.