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Horizontal Separation

Lateral and longitudinal

Horizontal separation keeps aircraft apart in the horizontal plane, and has two forms1:

  • Lateral: the aircraft are on different routes, or over different geographical locations.
  • Longitudinal: the aircraft are on the same, opposite or crossing routes, with a time or distance interval between them.

This page first covers procedural separation, based on position reports, estimates and distances reported by the pilot. Separation with ATS surveillance, measured on the screen, is at the end of the page, and it is the one you will use most of the time on the network.

When procedural separation appears on the network

Procedural separation is hardly used at the continental positions of Vatsim Brasil, because they have surveillance. It appears in oceanic control, when a target disappears from the screen, and in the departure minima, which the tower and the APP use even with radar. Read this part to understand the logic, and use it when surveillance is not available.

Lateral separation

By geographical locations

The simplest method: one aircraft reports being over one point and the other over another point, and the two locations are clearly different. The position may be determined visually or by reference to a navigation aid2.

By diverging routes

Two aircraft on routes diverging from the same aid or point are laterally separated when3:

Navigation Condition
VOR Radials diverging by at least 15°, and at least one aircraft 15 NM or more from the VOR
NDB Tracks to or from the NDB diverging by at least 30°, and at least one aircraft 15 NM or more from the NDB
GNSS, or VOR and GNSS Tracks diverging by 15° to 135°, and at least one aircraft 15 NM from the common point, from FL 010 to FL 190, or 23 NM, from FL 200 to FL 600

On opposite or crossing routes this is not enough. Establish vertical separation before the aircraft are within 15 NM of the aid or of the crossing point4.

Before using GNSS-based separation, confirm that the aircraft is navigating by GNSS and is not flying a lateral offset (SLOP)5. Do not use GNSS separation if the pilot reports a loss of RAIM6.

On published procedures

Aircraft departing or arriving on published procedures (SID, STAR, IAC) are laterally separated when the distance between the tracks is at least7:

Combination Distance
RNAV 1 with RNAV 1, RNP 1, RNP APCH or RNP AR APCH 7 NM
RNP 1, RNP APCH or RNP AR APCH with each other 5 NM

They are also separated when the protection areas of the tracks do not overlap.

In turns

If an aircraft's route includes a turn that will cause lateral separation to be lost, establish another separation before the aircraft starts the turn8. Remember that a fly-by turn may begin up to 20 NM before the waypoint and cut inside it. In a flyover turn, the aircraft overflies the waypoint and only then turns, ending up outside the turn8.

Longitudinal separation

What "same route" means

For longitudinal separation, the angular difference between the routes defines the case9:

Case Angular difference
Same route Less than 45°, or more than 315°
Opposite routes More than 135° and less than 225°
Crossing routes All other cases: 45° to 135°, and 225° to 315°

Watch the faster aircraft behind

The longitudinal minimum applies all the time, not only when you check it. If the following aircraft is faster than the preceding one, the distance between them decreases. When separation is about to reach the minimum, adjust speed to maintain it10.

Time-based

Time-based separation uses position reports and estimates, and is what you use without surveillance and without DME.

Situation Minimum Source
Same level, same route 15 min 11
Same level, same route, with aids that allow position and speed to be determined continuously 10 min 11
Same level, same route, preceding aircraft 20 kt or more faster (TAS) 5 min 11
Same level, same route, preceding aircraft 40 kt or more faster (TAS) 3 min 11
Same level, crossing routes, at the crossing point 15 min, or 10 min with aids 12
Opposite routes, without lateral separation Vertical from 10 min before to 10 min after the estimated crossing 13

The 5 and 3 minute minima only apply between aircraft that departed from the same aerodrome, between en-route aircraft that reported over the same point, or between a departure and an en-route aircraft that has already reported a point that ensures separation where the departure will join the route11.

On opposite routes, if it can be positively determined that the aircraft have passed each other, the 10 minutes after the crossing are no longer required13.

Climbing or descending

When one aircraft climbs or descends through another aircraft's level without vertical separation:

Situation Minimum Source
Same route 15 min 14
Same route, with aids that allow frequent determination of position and speed 10 min 14
Same route, with the level change started within 10 min of the second aircraft reporting over a reporting point 5 min 14
Crossing routes 15 min, or 10 min with aids 15

DME or GNSS distance

With DME or GNSS, distances reported by the pilots replace time. Both aircraft must be using the same DME station, a DME and a waypoint at the same location, or the same waypoint, and flying directly to or from it16. Keep direct VHF voice communication with both while applying this separation17. If both have area navigation, ask specifically for the GNSS distance18.

Situation Minimum Source
Same level, same route 20 NM 19
Same level, same route, preceding aircraft 20 kt or more faster (TAS) 10 NM 20
Same level, routes crossing at less than 90°, with distances from the same point at the crossing 20 NM, or 10 NM with 20 kt 21
Climbing or descending, same route, one of them maintaining level 10 NM 22
Opposite routes, after the crossing is confirmed 10 NM to climb or descend through the other's level 23

The distance must be checked with simultaneous readings from both aircraft, at frequent intervals19.

Departures

The ICA 100-37 departure minima complement the previous ones and apply between aircraft that have just taken off24:

Situation Minimum Source
Routes diverging by at least 45° immediately after take-off, so that lateral separation exists 1 min 25
Same route, with the preceding aircraft 40 kt or more faster 2 min 26
Same route, the following aircraft climbing through the preceding aircraft's level without vertical separation 5 min 27

For the 2 minute minimum, the speed difference during the climb may be better estimated from IAS than from TAS26.

Separation between a departure and an arrival at the same aerodrome is in Aerodrome Separation.

With ATS surveillance

With ATS surveillance, horizontal separation no longer depends on reports and is measured on the screen.

Situation Minimum Source
Separation with PSR, SSR, ADS-B or MLAT 5 NM 28
In the TMA or CTR, if only en-route radar is available 10 NM 28
Wake turbulence, if larger than the radar minimum See Wake Turbulence 29

The rules of application are:

  • The distance is measured between the centres of the targets. The edges must never touch or overlap without vertical separation30.
  • The minima only apply between identified aircraft, when identification is likely to be maintained31.
  • A departure may be separated by the surveillance minima from take-off, if it is likely to be identified within 1 NM of the end of the runway32.
  • The surveillance minima do not apply between aircraft in the same hold. Separate them vertically33.
  • If a controlled flight not yet identified enters your airspace, keep the identified aircraft separated from all targets on the screen until you identify it or establish procedural separation34.
  • If control will pass to a sector or unit that only provides procedural separation, establish that separation before the aircraft reaches the limit of your airspace or leaves surveillance coverage35.

How to measure and keep the 5 NM with vectors and speed is in the Vectoring and Sequencing Manual.

In EuroScope

F1 + D (.distance) shows the updated distance between an aircraft and another aircraft or point. F1 + S (.sep) predicts the point of closest approach between two aircraft. Use the latter before clearing a climb or descent through another aircraft's level. See Commands.

  1. ICA 100-37, Art. 334, and Art. 39, § 2°, item II. See ICA 100-37. ↩

  2. ICA 100-37, Art. 341. ↩

  3. ICA 100-37, Art. 342, § 1°, and Table 2. ↩

  4. ICA 100-37, Art. 343. ↩

  5. ICA 100-37, Art. 344. ↩

  6. ICA 100-37, Art. 346. ↩

  7. ICA 100-37, Art. 349. ↩

  8. ICA 100-37, Art. 338 and §§ 1° and 2°. ↩↩

  9. ICA 100-37, Art. 360. ↩

  10. ICA 100-37, Art. 357 and sole paragraph. ↩

  11. ICA 100-37, Art. 362. ↩↩↩↩↩

  12. ICA 100-37, Art. 363. ↩

  13. ICA 100-37, Art. 366. ↩↩

  14. ICA 100-37, Art. 364, § 1°. ↩↩↩

  15. ICA 100-37, Art. 365. ↩

  16. ICA 100-37, Arts. 367 and 368, caput and § 1°. ↩

  17. ICA 100-37, Art. 368, § 2°. ↩

  18. ICA 100-37, Art. 369. ↩

  19. ICA 100-37, Art. 370. ↩↩

  20. ICA 100-37, Art. 371. ↩

  21. ICA 100-37, Art. 372. ↩

  22. ICA 100-37, Art. 373. ↩

  23. ICA 100-37, Art. 374. ↩

  24. ICA 100-37, Art. 434. ↩

  25. ICA 100-37, Art. 435. ↩

  26. ICA 100-37, Art. 436 and sole paragraph. ↩↩

  27. ICA 100-37, Art. 437 and sole paragraph. ↩

  28. ICA 100-37, Art. 953 and §§ 1° and 2°. ↩↩

  29. ICA 100-37, Art. 956. ↩

  30. ICA 100-37, Arts. 948 and 949. ↩

  31. ICA 100-37, Art. 946. ↩

  32. ICA 100-37, Art. 951. ↩

  33. ICA 100-37, Art. 952. ↩

  34. ICA 100-37, Art. 950. ↩

  35. ICA 100-37, Art. 947. ↩