Runway separation
Runway separation
Runway management is the main task of every tower controller. Without a runway, an airport obviously makes no sense. Not only do we have to use our runway as efficiently as possible in order to fully utilize the airport's capacity, but we also have to protect it accordingly, as the critical flight phases of take-off and landing take place there. Runway separation was introduced for this purpose. But what actually is runway separation? It's actually quite simple:
The runway may only ever be occupied by one user at a time.
Now we just have to deal with a few more questions to clearly define the concept.
Who is considered a runway user?
- Landing aircraft (i.e. aircraft with active landing clearance)
- Aircraft taking off (i.e. aircraft with active take-off clearance)
- Vehicles on the runway e.g. inspecting the runway (not implemented on Vatsim)
How long is a user considered to be an active user of a runway and when is the runway free again for the next user?
- For aircraft taking off: The runway can be used again as soon as the departing aircraft has either
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overflown the end of the runway (image b) or
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vacated the runway to the side (picture a)
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For landing aircraft: The runway can be used again as soon as the aircraft has vacated the runway (image c). The runway is considered abandoned as soon as all parts of the aircraft have rolled over the stop bar of the CAT1 holding point.
An aircraft that is cleared for line-up (i.e. taxiing onto the runway, but without take-off clearance) does not count as a runway user. A line-up clearance can therefore be given in the following cases, even though the runway is still occupied according to the above criteria:
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After a landing aircraft has passed the point at which the waiting aircraft will taxi onto the runway
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After a departing aircraft has passed the point at which the waiting aircraft will taxi onto the runway
The procedure described on this page is also called “full” runway separation. Does this mean that there is a “half” runway separation, too? Not quite, but almost. There is also “reduced” runway separation (RRS), which is taught in the specific tower textbooks. A brief teaser: with reduced runway separation, under certain conditions the runway may be used more efficiently.
Intersecting runways
Many airports have intersecting runways either to compensate for prevailing weather conditions or to increase efficiency due to a lack of space. In Germany, Hamburg and Cologne are particularly well known for their intersecting runways.
As always, there are rules and regulations that must be observed when using the two runways simultaneously.
In this chapter, we will consider all possible combinations for using the runways.
Departure - Departure
In the case of two departures on intersecting runways, the second aircraft may only begin the take-off run if one of the following conditions is met:
The other aircraft is taking off and
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has taken off and has initiated a turn that excludes the possibility of undercutting the separation or
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has crossed the intersection.
Arrival - Departure
The situation is different if we have a preceding inbound, in which case the second aircraft on the intersecting runway may only begin the take-off run if one of the following conditions is met:
The other aircraft lands and
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has left the runway or
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has been instructed to stop before the intersection and has completed the landing roll or
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has crossed the intersection.
Abflug - Anflug
Bei einem abfliegenden Luftfahrzeug gefolgt von einem anfliegenden Luftfahrzeug auf der kreuzenden Piste, darf das folgende Luftfahrzeug den Anfang der Piste erst überfliegen, wenn eine der folgenden Bedingungen gegeben ist::
Das andere Luftfahrzeug startet und
- hat abgehoben und eine Kurve eingeleitet, die eine Staffelungsunterschreitung ausschließt
oder - hat die Kreuzung überquert.
Arrival - Arrival
The last possibility is a landing aircraft followed by another landing aircraft on the intersecting runway. The following aircraft may only fly over the runway threshold if one of the following conditions is met:
The other aircraft is landing and
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has left the runway or
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has been instructed to stop before the intersection and has completed the landing roll or
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has crossed the intersection.
Simultaneous use of intersecting runways
The simultaneous use of intersecting runways may only be authorized for two landing aircraft under the following conditions:
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One of the intersecting runways has an available distance between threshold and intersection of at least 2200 meters.
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An aircraft with a maximum take-off weight of up to 2000 kg lands on this runway.
All of the following conditions must additionally be met:
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VMC
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The braking action is not negatively affected.
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Both aircraft have been informed of the simultaneous landings.
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The aircraft landing on the 2200m runway has been instructed to stop before the intersection.
Reduced runway separation (RRS)
Reduced runway separation is not a mandatory part of S1 training.
Requirements
ATCOs can only use Reduced Runway Separation if the following aspects are fulfilled:
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The tailwind component on the ground must not exceed 5 knots
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Ground visibility must be equal to or greater than 5 kilometers
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The main cloud base must be at 1000ft AGL or higher
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Wake turbulence separation must be maintained at all times
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The braking effect on the runway must not be significantly impaired by precipitation
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On Vatsim, the braking effect is considered to be significantly impaired by precipitation: snow (SN), snow grains (SG), ice grains (PL), hail (GR) and rime (GS) - in other words, all precipitation except rain (RA) and drizzle (DZ)
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The following aircraft in the RRS sequence must receive traffic information about the preceding traffic
Aircraft categories
For the Reduced Runway Separation procedure, aircraft have been divided into three categories.
These three categories are:
Possible constellations
There are four different possible constellations of these categories on a runway. We will now look at these step by step with a focus on Reduced Runway Separation.
Departure behind departure
- The following departure receives traffic information about the leading departure.
- If all other criteria are met, the second departure may be cleared for take-off as soon as the first departure has taken off and is a defined distance away from the second departure. The distance is specified by the LFZ-KATs (aircraft categories):
Preceeding |
Suceeding |
Requirement |
CAT 1 / CAT 2 |
CAT 1 |
airborne and at a distance of 600m |
CAT 1 / CAT 2 |
CAT 2 |
airborne and at a distance of 1500m |
CAT 3 |
all |
airborne and at a distance of 2400m |
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As soon as the second departure has taken off, any applicable separation must exist.
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Example of application: First departure is a DV20 IFR, second departure a BE58 VFR. No separation must be established between the two aircraft in D(CTR), only wake turbulence separation, as the VFR is a departure. However, since light behind light does not require wake turbulence separation, I only have to consider the runway separation. Without Reduced Runway Separation, I would have to hold back the take-off clearance until the DV20 has flown over the end of the runway. Using RRS, I can now clear the following take-off as soon as the DV20 has taken off and is 1500 m away from the BE58. This means I can use the runway more effectively and have more capacity.
Arrival behind arrival
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The second approach receives traffic information about the approach ahead.
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If all other criteria are met, the second approach may be cleared for landing as soon as the first approach has landed and is a defined distance away from the threshold. Additionally, the first approach must continue moving and leave the runway without backtracking. Because the landing clearance is explicitly clearance to overfly the runway threshold, it must of course be issued before the threshold is crossed. If the criteria are not (yet) fulfilled, a missed approach must be instructed. The distance is specified by the LFZ-KATs (aircraft categories):
Preceeding |
Suceeding |
Clearance before |
Requirement |
CAT 1 / CAT 2 |
CAT 1 |
aircraft crosses runway threshold |
vacating runway and at least 600m from threshold |
CAT 1 / CAT 2 |
CAT 2 |
vacating runway and at least 150m from threshold | |
CAT 3 |
all |
vacating runway and at least 240m from threshold |
This situation may seem somewhat strange, as a landing clearance is issued even though there is another pilot still on the runway. However, if the distances are maintained, this is actually legal and is practiced in reality.
Arrival behind departure
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The approach receives traffic information about departure.
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If all other criteria are met, the approach may receive landing clearance as soon as the departure has taken off and is a defined distance away from the threshold. Because the landing clearance is explicitly clearance to overfly the runway threshold, it must of course be issued before the threshold is crossed. If the criteria are not (yet) fulfilled, a missed approach must be instructed. The distance is specified by the LFZ-KATs (aircraft categories):
Preceeding |
Suceeding |
Clearance before |
Requirement |
CAT 1 / CAT 2 |
CAT 1 |
aircraft crosses runway threshold |
airborne and at least 600m from threshold |
CAT 1 / CAT 2 |
CAT 2 |
airborne and at least 1500m from threshold | |
CAT 3 |
all |
airborne and at least 2400m from threshold |
Departure behind arrival
Reduced runway separation may not be used in this constellation.
Phraseology examples
German | English |
G: VERKEHR C172 FLIEGT *VON PISTE 25* AB | G: TRAFFIC C172 DEPARTING *ON RUNWAY 25* |
G: VERKEHR A320 IST *AUF PISTE 25* GELANDET | G: TRAFFIC A320 LANDED *ON RUNWAY 25* |
G: VERKEHR PA34 LANDET *AUF PISTE 25* | G: TRAFFIC PA34 LANDING *ON RUNWAY 25* |
Miscellaneous and example
Example of the procedure
Marker in the sector file
Article about Reduced Runway Separation
Anyone interested in the topic of RRS beyond the content mentioned above will find an interesting article on the subject in an issue of “Flugleiter”, the magazine of the air traffic controllers’ union. It can be found from page 48 onwards.
Flugleiter 04/22