Introduction — Page 130, Lesson 148

Let's begin the Performance chapter. I want to walk you through the definitions first, because every calculation and every decision you make as a pilot in this subject hangs on these exact terms. We'll go through them in order. First, Absolute Ceiling. This is the altitude at which the theoretical rate of climb, with all engines operating at maximum continuous power, is reduced to zero feet per minute. So imagine climbing until you can no longer climb at all — that's your absolute ceiling. Note the qualifiers: all engines running, and maximum continuous power, not take-off power. And it's theoretical, because in practice you'd never fly right at that knife-edge. Next, Accelerate-stop Distance Available, often abbreviated ASDA. This is the distance from the point on the surface of the aerodrome at which the aeroplane can commence its take-off run, to the nearest point in the direction of take-off at which the aeroplane cannot roll over the surface of the aerodrome and be brought to rest in an emergency without the risk of accident. In plain terms: it's the total runway plus stopway you have to accelerate, then stop, if you reject the take-off. It is equal to TORA — that's Take-off Run Available — plus any available stopway. So ASDA = TORA + stopway. Now, Aerodrome. This is any area of land or water designed, equipped, set apart or commonly used for affording facilities for the landing and departure of aircraft. It includes any area or space, whether on the ground, on the roof of a building or elsewhere, which is designed, equipped or set apart for affording facilities for the landing and departure of aircraft capable of descending or climbing vertically — that's your helicopters and VTOL types. But it shall not include any area the use of which for affording facilities for the landing and departure of aircraft has been abandoned and has not been resumed. So an old disused strip doesn't count. Aerodrome Elevation — this is simply the elevation of the highest point of the landing area. Aerodrome Reference Point, or ARP — this is the geographical location of the aerodrome and the centre of its traffic zone where an ATZ, an Aerodrome Traffic Zone, is established. So it's the reference point for the whole aerodrome. Aerodynamic Ceiling — this one's different from absolute ceiling. It's the altitude, in unaccelerated 1g level flight, where the Mach number for the low speed and high speed buffet are coincident. So as you climb, the low-speed buffet Mach number rises and the high-speed buffet Mach number falls, and at the aerodynamic ceiling they meet. That's your absolute aerodynamic limit in level flight. Aeroplane — a power-driven heavier-than-air aircraft, deriving its lift in flight chiefly from aerodynamic reactions on surfaces which remain fixed under given conditions of flight. So fixed-wing, powered. And Aircraft — a machine that can derive support in the atmosphere from the reactions of the air. That's the broad umbrella term covering aeroplanes, helicopters, everything. Now, I want to show you the physical layout of these runway elements. Let me bring up a figure. That's Figure 2.1 — clearways extend from the end of the runway with an upward slope not exceeding 1.25%. And here's the stopway. Figure 2.2 — stopways are able to support the aeroplane during a rejected take-off and are marked by large yellow chevrons. And Figure 2.3 shows both together at an aerodrome. So you can see how TORA, ASDA, and the clearway all fit together on the physical surface. That's the foundation. We'll build the performance calculations on these definitions next.