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about the separation between departing aircraft and the following landing aircraft

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about the separation between departing aircraft and the following landing aircraft

Old 6th Jul 2020, 14:53
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Smile about the separation between departing aircraft and the following landing aircraft

in chapter 8 of ICAO doc 4444 -ATS surveillance services, the separation between the departing aircraft and following arrival aircraft is not specified, so, when can the controller in tower can instruct an aircraft to take off based on the position of arrival aircraft on final ? and what's the logic behind it?

and in this article: "Two minutes are required between take-offs when the preceding aircraft is 74 km/h (40 kt) or more faster than the following aircraft and both aircraft will follow the same track" what kind of speed does it mean ? cruising speed or the actual speed in the phase of departure?
thanks!
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Old 6th Jul 2020, 15:16
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Originally Posted by mxwbuaa
in chapter 8 of ICAO doc 4444 -ATS surveillance services, the separation between the departing aircraft and following arrival aircraft is not specified, so, when can the controller in tower can instruct an aircraft to take off based on the position of arrival aircraft on final ? and what's the logic behind it?

and in this article: "Two minutes are required between take-offs when the preceding aircraft is 74 km/h (40 kt) or more faster than the following aircraft and both aircraft will follow the same track" what kind of speed does it mean ? cruising speed or the actual speed in the phase of departure?
thanks!
The standard surveillance separation is 5 nm, or any other depending on the minimum separation the unit has. And that is the surveillance separation between arrivals and departures as well.

What most approach controllers do, is either by standard agreement between TWR and APP, or individually, release aircraft with reference to arriving aircraft. Then the TWR controller can apply "reduced separation in vicinity of an airport", hence see both aircraft and determine there is no risk of collision, and thereby get well below normal surveillance separation.

On days with bad weather, where the "vicinity separation" also known as TWR-separation, cannot be used, there are a few "procedural separations", like the departure has to depart before the arrival reaches 5 NM final etc. Most TWR controllers will gladly accept releases with reference to arriving aircraft, and apply whatever separation is available depending on weather.

40 kts? It says 40 kts.... so the speed difference has to be 40 kts... if you take the TAS from their flightplan, I'd say you need to have a chat with your OJTI again.... But that could vary from place to place... but the way I was taught was we consider actual speed of the aircraft. (I've seen TAS from the flightplan used during basic training, just for the students to get a feel for it, and not "overburden" them)
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Old 7th Jul 2020, 06:43
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Aircraft are deemed to be separated if the distance between them is constant or increasing thus as a departure is accelerating and an arrival is decelerating, it's up to the tower controller to decide the departure separation.
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Old 7th Jul 2020, 09:09
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Aircraft are deemed to be separated if the distance between them is constant or increasing thus as a departure is accelerating and an arrival is decelerating, it's up to the tower controller to decide the departure separation.
And your reference for that sweeping statement?

2 s
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Old 7th Jul 2020, 18:00
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In an ICAO environment the departing aircraft needs to have crossed the upwind end of the runway prior to the arriving aircraft crossing the landing threshold. This assumes no reduced runway separation (RRSM) is being used. How the tower controller achieves it is usually based on experience, but will be dependent on weather conditions also i.e. VMC/IMC.
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Old 7th Jul 2020, 19:02
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Originally Posted by Red Dragon
In an ICAO environment the departing aircraft needs to have crossed the upwind end of the runway prior to the arriving aircraft crossing the landing threshold. This assumes no reduced runway separation (RRSM) is being used. How the tower controller achieves it is usually based on experience, but will be dependent on weather conditions also i.e. VMC/IMC.
Or on a nice sunny day: Wheels up before Wheels down!
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Old 8th Jul 2020, 03:51
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Originally Posted by terrain safe
Or on a nice sunny day: Wheels up before Wheels down!
In the UK yes, but ICAO runway separation requires the departing to have crossed the upwind end of the runway - irrespective of the weather conditions. Quite restrictive when you've got a 4500m runway!
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Old 8th Jul 2020, 07:47
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Originally Posted by Red Dragon
In the UK yes, but ICAO runway separation requires the departing to have crossed the upwind end of the runway - irrespective of the weather conditions. Quite restrictive when you've got a 4500m runway!
....as does the forthcoming EASA Part.ATS...
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Old 8th Jul 2020, 10:48
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Originally Posted by Gonzo
....as does the forthcoming EASA Part.ATS...
The "runway separation" is the only directly defined separation for us TWR controllers... technically we just have to ensure that separation.... and that goes for IFR and VFR. Though there's the either "passed the upwind, or have started a turn out", which is really helpfull when squeezing in those VFR departures.

(Other than that, we fall under the "safe, orderly and expeditious flow" and "prevent collision". But that "runway separation" is ofcourse not something approach can use as a separation (where I've worked at least), they only have the option of having tower help with the "reducing separation in vicinity of airport" for them.)
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Old 8th Jul 2020, 13:26
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Originally Posted by jmmoric
The standard surveillance separation is 5 nm, or any other depending on the minimum separation the unit has. And that is the surveillance separation between arrivals and departures as well.

What most approach controllers do, is either by standard agreement between TWR and APP, or individually, release aircraft with reference to arriving aircraft. Then the TWR controller can apply "reduced separation in vicinity of an airport", hence see both aircraft and determine there is no risk of collision, and thereby get well below normal surveillance separation.

On days with bad weather, where the "vicinity separation" also known as TWR-separation, cannot be used, there are a few "procedural separations", like the departure has to depart before the arrival reaches 5 NM final etc. Most TWR controllers will gladly accept releases with reference to arriving aircraft, and apply whatever separation is available depending on weather.

40 kts? It says 40 kts.... so the speed difference has to be 40 kts... if you take the TAS from their flightplan, I'd say you need to have a chat with your OJTI again.... But that could vary from place to place... but the way I was taught was we consider actual speed of the aircraft. (I've seen TAS from the flightplan used during basic training, just for the students to get a feel for it, and not "overburden" them)

but in non-radar environment or just procedural control environment , how can you know in real time the actual speed of a departing aircraft the speed of which is increasing ?
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Old 8th Jul 2020, 17:22
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Originally Posted by Gonzo
....as does the forthcoming EASA Part.ATS...
AltMoC can be developed to address this at those aerodromes where it might be an issue
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Old 9th Jul 2020, 12:02
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Originally Posted by LookingForAJob
Ask the pilot.
Thank you...

I was just about to say the same...
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Old 9th Jul 2020, 14:13
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Originally Posted by LookingForAJob
Ask the pilot.
If you can't judge it visually then yes, although I've never felt the need to do that to an arrival inside 4nm or so. A knowledge of aircraft performance is usually enough and if you're fortunate enough to have radar in the tower then reference to ground speed/Mode S usually does the trick.
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Old 9th Jul 2020, 18:00
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Originally Posted by usedtobeATC
I gave clearance for take off when arriving traffic was not less then 2.5 miles before RW (VMC). I did it for 42 years as a Tower controller.
NATS controllers at Gatwick did it at a shorter range than that; I was on the flight deck of a '737 and from 4 mile final, 3 aircraft were cleared for departure before we got landing clearance.
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Old 9th Jul 2020, 18:35
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NATS controllers at Gatwick did it at a shorter range than that; I was on the flight deck of a '737 and from 4 mile final, 3 aircraft were cleared for departure before we got landing clearance.
All of which illustrates that Gatwick is (or was, prior to current traffic reduction) an incident waiting to happen, but does not address the OP's query.

2 s
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Old 10th Jul 2020, 08:07
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Originally Posted by 2 sheds
All of which illustrates that Gatwick is (or was, prior to current traffic reduction) an incident waiting to happen, but does not address the OP's query.

2 s
thats quite a statement!

others might describe Gatwick as the worldwide standard bearer for efficient single runway operations.
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Old 10th Jul 2020, 14:49
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4 miles final and 3 departures? That’s 3 departures in less than 2 minutes.... if your 737 is doing 120 on final, and the departures use 40 seconds to get airborne... it’s barely doable.

I’d personally believe in 2 departures.... unless something small you can get out of the way fast.
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Old 10th Jul 2020, 17:20
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Originally Posted by usedtobeATC
Interesting display! What do you do with it?
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Old 10th Jul 2020, 19:19
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Originally Posted by chevvron
NATS controllers at Gatwick did it at a shorter range than that; I was on the flight deck of a '737 and from 4 mile final, 3 aircraft were cleared for departure before we got landing clearance.
But only two departures on this occasion? ..........

Originally Posted by chevvron
Coming back to Gatwick on a fam flight once in a 737, we were a 4 miles on 08 and they still had time to launch 2 before we got landing clearance.
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Old 10th Jul 2020, 23:10
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Wake turbulence is an increasing threat in the training world - at one airfield in particular with a low to medium flow rate I/my student has been well inside 4nm (Light) when a departure (Medium or greater) has been released. Marginal but manageable, except we're planned/announced to go around not to land. And a reasonable headwind, putting the ensuing wake turbulence neatly in our climbout lane. Individual tower controllers vary with awareness and negotiation on this - some are excellent once the issue has been recognised by offering alternatives, others are perhaps not as aware from the training or organisational background.

Training is complex for all, but the majority of instrument training does need the full approach to be truly valid - particularly on a test where to complete an approach for my candidate they need the opportunity to fly it to procedure minima. On the flip side, while training traffic may be a little slower to respond to calls/not perfectly accurate at times, all IFR training is done with a suitably qualified adult observing/commanding, which ought to control the risk level a bit.

Really very happy to discuss this with ATCOs/arrange liaison flights once easily possibly to try and foster understanding on all sides, since ultimately we're all working towards the same aim of minimum paperwork/maximum achievement!
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