Separation — Page 303, Lesson 395

Right, let's pick this up with the crossing tracks case. We've just dealt with the same track scenario, so now we're looking at what happens when two aircraft are on tracks that actually cross each other. The basic standard here is 15 minutes. That's the default separation you need at the crossing point. But, and this is a recurring theme, if the frequent determination of position and speed caveat applies, the standard may be reduced to 10 minutes. So, if you can frequently and accurately determine where both aircraft are and how fast they're going, you can tighten that separation down from 15 to 10 minutes. Now, let's move on to a more complex case: climbing or descending. This is where things get interesting. The problem only exists when vertical separation does not exist. In other words, the aircraft are within the vertical separation standard of each other. If they're already separated vertically, you don't have a problem. But if they're not, you need to think about their relative tracks, and now we also bring in the reciprocal track case. Let's break this down by track type. First, the same track case. When an aircraft will pass through the level of another aircraft on the same track, the separation applied is 15 minutes. But, that can be reduced to 10 minutes, provided that navigation aids permit frequent update of position and speed, and this is approved by the authority. So, you need the equipment and the official approval to use that reduced standard. Alternatively, you can go down to 5 minutes, provided that the level change is commenced within 10 minutes of the time that the second aircraft has reported over an exact reporting point. So, the timing of when you start the climb or descent is critical here. Now, there's an important note about this. If the level change involved is considerable, an intermediate level just above or just below, depending on whether it's a climb or a descent, may be allocated to the manoeuvring traffic. Once at that level, separation will be assessed, and if applied, the level crossing manoeuvre approved and executed. So, for a big altitude change, you don't just go straight through. You stop at an intermediate level, check your separation, get approval, and then complete the crossing. Next, we have the crossing tracks case for climbing or descending. The applicable standard is 15 minutes, unless frequent update of position and speed is available, in which case the minimum is reduced to 10 minutes. Same pattern as before. Finally, we have the reciprocal tracks case. This is the head-on scenario. Where lateral separation is not provided, vertical separation shall be provided for at least 10 minutes prior to and after the time the aircraft are estimated to have passed. So, you need that vertical buffer for a full 10 minutes before and 10 minutes after the estimated passing time. Once it has been established, usually visually, that the aircraft have indeed passed, this minimum need not then further apply. So, once you're sure they've passed each other, you can relax that requirement. Let me show you what these look like. This figure illustrates the intermediate level concept we just discussed. And shows the reciprocal track case. So, to summarise the climbing or descending rules: same track gives you 15 minutes, reducible to 10 with frequent updates, or 5 if you start the level change within 10 minutes of a report over an exact reporting point. Crossing tracks give you 15 minutes, reducible to 10 with frequent updates. And reciprocal tracks require vertical separation for 10 minutes before and after the estimated passing time, unless you've visually confirmed they've passed.