Aerodromes - Physical Characteristics — Page 381, Lesson 513

Let’s pick up with the declared distances. We’ve already covered TORA, the take-off run available. Now I want to walk you through the other three declared distances, because they’re the ones that actually govern what an aeroplane can do on take-off and landing. First, TODA — Take-Off Distance Available. The definition is precise: it’s the distance from the start of TORA to the nearest obstacle in the direction of take-off that projects above the surface of the aerodrome and is capable of affecting the safety of an aeroplane in flight. There’s a hard cap on this: it can’t exceed 1.5 times TORA. In practice, TODA is usually TORA plus the clearway, if a clearway exists. So think of the clearway as that obstacle-free space beyond the runway that lets the aeroplane climb out safely. Next, ASDA — Accelerate-Stop Distance Available. The definition: it’s the distance from the start of the take-off run to the nearest point in the direction of take-off at which the aircraft cannot roll over the surface and be brought to rest in an emergency without risk of accident. In plain terms, it’s the distance you have to accelerate on take-off, then abort and stop safely if something goes wrong. ASDA used to be called EDA — Emergency Distance Available — so you’ll sometimes see that older term. Usually ASDA is TORA plus the stopway, if a stopway is available. The stopway is that paved area beyond the runway designed to let you stop in an aborted take-off. Then LDA — Landing Distance Available. The definition: it’s the distance from the point where an aeroplane can commence its landing to the point where the surface is incapable of bearing the mass of the aircraft under normal operating conditions. Usually this is the full length of the runway, but it may include a paved stopway, if available, where the threshold is displaced. So if the threshold is moved back, the LDA can extend into that paved stopway. Now, here’s the key relationship: these four distances are all declared for each runway, and they’re not necessarily the same. TORA is the run available. TODA adds the clearway for climb-out. ASDA adds the stopway for aborting. LDA is what you have for landing. The figure shows exactly how each one is built up — TORA/TODA/ASDA/LDA with the clearway and stopway marked. Now let’s move to the condition of the movement area and related facilities. This is about reporting. Information on the condition of the movement area — that’s the runways, taxiways, aprons — and the operational status of related facilities must be provided to the appropriate aeronautical information service units. Similar information of operational significance must go to the air traffic service units. The purpose is to enable those units to provide the necessary information to arriving and departing aircraft. The information must be kept up to date, and changes in conditions must be reported without delay. The condition of the movement area and the operational status of related facilities are to be monitored, and reports on matters of operational significance or affecting aircraft performance must be given — particularly in respect of the items that follow in the next part of the chapter.