Separation — Page 309, Lesson 407

Let's pick up with the heavy category indication, because that's the first thing this passage wants you to understand. When an aircraft is in the heavy wake turbulence category, it creates a wake that is genuinely dangerous to lighter aircraft following behind it. So the rule is: the pilot of a heavy category aircraft must announce that fact in the very first radio-telephony contact with an air traffic control unit. They do this by adding the suffix "heavy" to their identifying call sign. So instead of just "Speedbird 216," the pilot says, "London Control this is Speedbird 216 heavy on 133.650." That single word tells the controller immediately, before anything else, that this aircraft needs extra separation because of its wake. Now, why does this matter? Because wake turbulence separation is handled differently depending on whether the controller can see the aircraft on radar. When radar is being used, the controller can see the exact position of every aircraft on the screen. So in that case, the required separation for wake turbulence is expressed in distance — in nautical miles. This is what we call radar wake turbulence separation. Let me give you the actual ICAO minima, because you need to know these cold. The table gives you the separation based on the wake turbulence category of the leading aircraft and the following aircraft. If a heavy is leading and a heavy is following, the separation is 4 nautical miles. If a heavy is leading and a medium is following, it's 5 nautical miles. If a heavy is leading and a light is following, it's 6 nautical miles. And if a medium is leading and a light is following, it's 5 nautical miles. Now, there's a very important note here. These criteria apply where the category of the following aircraft is lighter than the leading aircraft — except for the heavy/heavy case. So the heavy/heavy case is the one exception where the following aircraft is the same category, not lighter, and you still apply separation. That's because even a heavy aircraft following another heavy can be affected by the wake. So you need to remember that exception clearly. Now let's move to visual separation in the vicinity of aerodromes. This is a different philosophy entirely. Except when low visibility operations are in progress at an aerodrome, traffic flying in the vicinity — that includes arriving, departing, and local area traffic — will be flying in conditions that either permit VFR, or permit pilots to maintain separation from other aircraft visually. The importance of this cannot be overstressed. Why? Because applying visual separation relieves the air traffic control officer from having to impose either procedural or radar separation. And that's a huge relief, because it permits minimum runway occupancy time, it permits "land after" procedures, and it permits multiple aircraft to fly in the visual traffic pattern. In effect, the application of visual separation increases aerodrome capacity and hence aerodrome utilization. Let me give you a concrete example. Heathrow has the capacity to accommodate about 60 take-off operations and 60 landing operations per hour. At peak time, the traffic load gets close to that. If procedural or radar separation had to be applied to the arrival or departure phases, the utilization would reduce dramatically. So visual separation is what allows that high throughput. Now, the standards previously mentioned can be reduced under certain conditions. There are three specific cases. First, adequate separation can be provided by the aerodrome controller when each aircraft is continuously visible to the controller. Second, flight crews report that they have visual contact with other aircraft and this can be maintained. Third, in the case of one aircraft following another, the crew of the following aircraft report that the leading aircraft is within sight and that separation can be maintained. So to tie it all together: you have the heavy call sign suffix as the trigger, radar wake turbulence separation as the distance-based minima when the controller has radar, and visual separation as the capacity-enhancing alternative when conditions allow pilots or the controller to see the traffic. Each has its own conditions and its own purpose.