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Aerodrome Separation

One aircraft on the runway at a time

In the tower, the most important separation is not measured in miles or feet, but in who is on the runway. The general rule is simple: a runway in use has only one aircraft taking off or landing at a time. The wake turbulence minima add to it. The more restrictive of the two always applies.

Departures

An aircraft does not start its take-off roll until1:

  • the preceding departing aircraft has crossed the end of the runway or started a turn; and
  • all preceding landing aircraft are off the runway.

Arrivals

An aircraft does not cross the threshold on final approach until2:

  • the preceding departing aircraft has crossed the end of the runway or started a turn; and
  • all preceding landing aircraft have vacated the runway.

If you cannot see whether the aircraft has vacated the runway, either from the window or on surveillance, ask it to report. The report only counts when the entire aircraft is beyond the runway-holding position3.

TAM 3320, on the ground at 10, taxi via first intersection to the right, report runway vacated.

Clearance in advance

You do not need to wait for the runway to be clear to issue a clearance. A take-off clearance may be issued when it is likely that separation will exist when the aircraft starts its take-off4. The same reasoning applies to landing. But if separation does not materialise, you must cancel the clearance in time.

The take-off clearance always includes the runway designator5. To save time, you may issue a clearance for an immediate take-off before the aircraft enters the runway. On accepting it, the pilot enters and takes off without stopping6.

TAM 3203, runway 09 left, cleared for immediate take-off, wind 095 degrees, 10 kt.

Good practice

On the network, many pilots take a while to line up and take off. If you are fitting a departure between two arrivals, first ask whether they can accept an immediate take-off. If they cannot, keep them waiting at the holding point.

Conditional clearances

Conditional phrases such as "behind landing aircraft" or "after departing aircraft" may only be used for movements on the runway in use when both the controller and the pilot can see the aircraft or vehicle causing the condition. The aircraft causing the condition always goes first7.

GLO 1256, report the Airbus on final in sight.

*GLO 1256, Airbus in sight.

GLO 1256, behind Airbus on final, line up and wait behind.

Departure sequence

Departures normally go in the order in which they are ready, but you may change the order to release more aircraft with less delay. Consider, among other factors8:

  • each aircraft's type and performance;
  • the routes after take-off;
  • minimum intervals between take-offs;
  • wake turbulence minima;
  • priorities.

In practice

The departure order decides how much wake time you spend. Two MEDIUMs followed by a LIGHT spend 2 minutes of wake time on the last one alone. A LIGHT right behind a HEAVY also spends 2 minutes, and a LIGHT placed before the HEAVY spends none. When possible, group aircraft of the same category and release the lighter ones first.

Think about the route too. Two aircraft turning in opposite directions after take-off can depart 1 minute apart. Two following the same SID at the same speed need much more if the APP has no radar. The departure minima are in Horizontal Separation.

Departures and arrivals

A take-off may be cleared based on the position of an arriving aircraft. Without ATS surveillance, ICA 100-37 gives these rules9:

The arrival is flying The departure may take off
A complete procedure, before starting the procedure turn or base turn onto final In any direction
A complete procedure, after starting the procedure turn or base turn In a direction differing by at least 45° from the reciprocal of the approach direction, up to 3 min before the arrival's expected time over the threshold
A straight-in approach In any direction, up to 5 min before the arrival's expected time over the threshold
A straight-in approach In a direction differing by at least 45° from the reciprocal of the approach direction, up to 3 min before the expected time over the threshold, or before the arrival crosses a designated point on the approach track

If the arrival is on a STAR or an RNAV or RNP approach, the departure may take off on a track that stays outside the protection area of the procedure, provided that there is vertical separation until the arrival passes a waypoint designated by the unit, and that the take-off happens before the arrival passes another designated waypoint10. These points are in the unit's operational model and, on the network, in the aerodrome MOP, where they exist.

With ATS surveillance, the APP separates the departure from the arrival by the radar minima, provided the departure is identified within 1 NM of the end of the runway11. In practice, the tower agrees with the APP on the interval between the arrival and the take-off, and the APP ensures separation in the air.

Reduced runway separation minima

ICA 100-37 allows minima smaller than the clear-runway rule, on runways where DECEA establishes them after a risk assessment and publishes them in the AIP. They only apply in daytime, with visibility of at least 5 km, a ceiling of at least 1,000 ft and a tailwind of up to 5 kt, among other conditions. Wake separation still applies12.

For this, aircraft are divided into three categories13:

Category Aircraft
1 Single-engine propeller aircraft up to 2,000 kg
2 Single-engine propeller aircraft over 2,000 kg and under 7,000 kg, and twin-engine propeller aircraft under 7,000 kg
3 All others

The preceding aircraft must have passed 600 m, 1,500 m or 2,400 m from the threshold, depending on the categories involved14. Reduced minima never apply between a departure and a preceding landing15.

On the network

Use reduced minima only where the aerodrome MOP provides for them. Everywhere else, apply the clear-runway rule.

Wake turbulence on the runway

The wake turbulence times for landings and departures, including intersections, displaced thresholds and opposite directions, are in Wake Turbulence.

  1. ICA 100-37, Art. 602 and §§ 1° to 3°. See ICA 100-37. ↩

  2. ICA 100-37, Art. 611 and §§ 1° to 3°. ↩

  3. ICA 100-37, Art. 570 and sole paragraph. Phraseology from MCA 100-16, Art. 133. See MCA 100-16. ↩

  4. ICA 100-37, Art. 603. ↩

  5. ICA 100-37, Art. 606, sole paragraph. ↩

  6. ICA 100-37, Art. 607 and sole paragraph. Phraseology from MCA 100-16, Art. 126. ↩

  7. MCA 100-16, Art. 49 and §§ 1° and 2°. ↩

  8. ICA 100-37, Art. 597, § 1°. ↩

  9. ICA 100-37, Arts. 469 to 471. ↩

  10. ICA 100-37, Art. 472 and §§ 1° and 2°. ↩

  11. ICA 100-37, Art. 951. ↩

  12. ICA 100-37, Arts. 619 to 621 and 624. ↩

  13. ICA 100-37, Art. 622. ↩

  14. ICA 100-37, Art. 625. ↩

  15. ICA 100-37, Art. 623. ↩