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!

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)

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

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! :O

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...

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.)

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 ?

AltMoC can be developed to address this at those aerodromes where it might be an issue

Thank you...

I was just about to say the same...

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.

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

thats quite a statement!

others might describe Gatwick as the worldwide standard bearer for efficient single runway operations.

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.

Interesting display! What do you do with it?