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In the future, is it possible to apply in the same airspace different separations between pairs of aircraft? Depending on the relative speed, navigation capacity of the aircraft, intersection geometry, etc.

What will be necessary to be able implement this type of separation?

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    $\begingroup$ Welcome to aviation.SE! This question might have some useful information. The tour is a good way to learn more about how the site works. $\endgroup$
    – Pondlife
    Mar 20 '20 at 17:57
  • $\begingroup$ this question is speculative. speculation are off topic as defined by the help center $\endgroup$
    – Manu H
    Apr 1 '20 at 7:38
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There already is, to some extend.

Firstly, there is a big difference between separation in surveillance environments and non-radar environments. In non-radar environments, the separation minima are much larger, because separation is based on position reports provided by the aircraft, which is deemed less accurate than radar data.

In radar environments, the separation needed is generally 5 NM. However, in many terminal areas this is reduced to 3 NM - but only for aircraft going 250 KIAS or less (so, reduced relative speed). Moreover, on final approach, separation is commonly reduced to 2,5 NM - again, since the planes are going slow and pointing in the same direction (the runway), the relative speed is low.

Note that the navigation capabilities of individual aircraft does not matter, since separation is based on ground based equipment (radar), NOT on position information provided by the aircraft.

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  • $\begingroup$ Thanks, I understand that, but in radar enviroment, is there any possibility to have dynamic longitudinal separations depending on the pair of aircraft in the future? eg: depending on the wake turbulence $\endgroup$
    – Paula
    Mar 20 '20 at 19:05
  • $\begingroup$ @Paula Already exists. Wake turbulence separation minima range from 4 to 8 NM depending on the involved aircraft $\endgroup$ Mar 20 '20 at 19:24
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If your question is prompted strictly by a concern for wake turbulence as one of your previous comments suggests, rest assured that Wake Turbulence Avoidance is already addressed in US pilot training and ATC procedures and protocol. Each aircraft is placed into a wake turbulence category. And both pilots and controllers follow specific rules of engagement depending on the traffic environment and aircraft involved. Pilots of light aircraft even have a safety out (3 minute separation cushion) when it comes to accepting takeoff clearance in a high wake turbulence environment.

As far as “ relative speed, navigation capacity of the aircraft, intersection geometry, etc.”, that is less of a concern in the terminal environment. For instance:

  1. Relative speed is less of a concern when everyone except for hose in a Class B airspace must slow down below 200 knots when approaching an airfield’s airspace. Everyone below 10,000 feet must slow down below 250 knots. Anyone in a Class B airspace must fly at the speed assigned directly to them by ATC. If one is not assigned, they can not exceed 250 knots. And, everyone inside Class B airspace must be under the control of ATC. And any airfield with an operating control tower must give each aircraft their own individual clearances to use an IAP, join the traffic pattern, or to land.
  2. Regardless of an aircraft’s means of navigation, all aircraft are roughly following the same basic routes and rules. Even an airplane flying on a route not specified has to follow specific altitude rules. And, communication protocols must be followed in all but uncontrolled airspace. Even then, protocols are highly recommended unless the aircraft does not have a means of communication. Imagine multiple families going on the same road trip. Regardless of whether they all use a different means to get directions (Garmin, TomTom, Mapsco, Googlemaps on their phone, Waze, or their innate sense of direction and a list of landmarks), they should all arrive to their destination.
  3. Except for airport environments where you are under direct ATC control, you are a small airplane in a big sky. In and around airfield’s airspace, training areas, victor airways, Navaids, etc., you are less likely to encounter another aircraft. In today’s age of GPS providing point-to-point direct routing, the use of victor airways and NavAids is less important. Giving rise to more open space to fly with less airway congestion. Regardless, you are required to practice extreme vigilance, monitoring the outside air to practice “See and Avoid” discipline.

The Airmen Information Manual has this to say about the subject...

7–3–9 Air Traffic Wake Turbulence Separations

a. Because of the possible effects of wake turbulence, controllers are required to apply no less than minimum required separation to all aircraft operating behind a Super or Heavy, and to Small aircraft operating behind a B757, when aircraft are IFR; VFR and receiving Class B, Class C, or TRSA airspace services; or VFR and being radar sequenced.

  1. Separation is applied to aircraft operating directly behind a super or heavy at the same altitude or less than 1,000 feet below, and to small aircraft operating directly behind a B757 at the same altitude or less than 500 feet below:

(a) Heavy behind super—6 miles.

(b) Large behind super—7 miles.

(c) Small behind super—8 miles.

(d) Heavy behind heavy—4 miles.

(e) Small/large behind heavy—5 miles.

(f) Small behind B757—4 miles.

  1. Also, separation, measured at the time the preceding aircraft is over the landing threshold, is provided to small aircraft:

(a) Small landing behind heavy—6 miles.

(b) Small landing behind large, non-B757 —4 miles.

Reference: Pilot/Controller Glossary—Aircraft Classes

b. Additionally, appropriate time or distance intervals are provided to departing aircraft when the departure will be from the same threshold, a parallel runway separated by less than 2,500 feet with less than 500 feet threshold stagger, or on a crossing runway and projected flight paths will cross:

  1. Three minutes or the appropriate radar separation when takeoff will be behind a super aircraft;

  2. Two minutes or the appropriate radar separation when takeoff will be behind a heavy aircraft.

  3. Two minutes or the appropriate radar separation when a small aircraft will takeoff behind a B757.

Note: Controllers may not reduce or waive these intervals.

c. A 3-minute interval will be provided when a small aircraft will takeoff:

  1. From an intersection on the same runway (same or opposite direction) behind a departing large aircraft (except B757), or

  2. In the opposite direction on the same runway behind a large aircraft (except B757) takeoff or low/missed approach.

Note: This 3-minute interval may be waived upon specific pilot request.

d. A 3-minute interval will be provided when a small aircraft will takeoff:

  1. From an intersection on the same runway (same or opposite direction) behind a departing B757, or

  2. In the opposite direction on the same runway behind a B757 takeoff or low/missed approach.

Note: This 3-minute interval may not be waived.

e. A 4-minute interval will be provided for all aircraft taking off behind a super aircraft, and a 3-minute interval will be provided for all aircraft taking off behind a heavy aircraft when the operations are as described in subparagraphs b1 and b2 above, and are conducted on either the same runway or parallel runways separated by less than 2,500 feet. Controllers may not reduce or waive this interval.

f. Pilots may request additional separation (i.e., 2 minutes instead of 4 or 5 miles) for wake turbulence avoidance. This request should be made as soon as practical on ground control and at least before taxiing onto the runway.

Note: 14 CFR Section 91.3(a) states: “The pilot-in-command of an aircraft is directly responsible for and is the final authority as to the operation of that aircraft.”

g. Controllers may anticipate separation and need not withhold a takeoff clearance for an aircraft departing behind a large, heavy or super aircraft if there is reasonable assurance the required separation will exist when the departing aircraft starts takeoff roll.

Note: With the advent of new wake turbulence separation methodologies known as Wake Turbulence Recategorization, some of the requirements listed above may vary at facilities authorized to operate in accordance with Wake Turbulence Recategorization directives.

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