Separation between arrival and departure aircraft

[ericliu]

Hi everybody:
I have a question about the separation between arrival and departure aircraft,one aircraft is on final approach while another departure aircraft is holding short of runway, at what distance for the landing one from touchdown can the tower controller authorise the departure one to get onto the runway for take off, and in this scenario, what separation standard shall the tower controller use?
Thank for any replies!

[radar707]

Any distance that the controller thinks that he can safely get the departure airborne, as a general rule of thumb, where I work, if the arrival is outside 3.5 miles (depending on wind conditions, weather, departing aircraft type {not a heavy} ) then it is possible to depart an aircraft ahead.

If the gap is tight then I am using reduced separation in the vicinity of an aerodrome. Some units have deemed separations between arrivals and departures in tight gaps (providing the departing aircraft is xxxx metres along the runway when the arrival reaches the threshold then they are deemed separated and a "land after the departing" clearance can be issued)

[ron83]

yep,a lot could depend on local procedures,in our place,when aircraft crossed 5 nm final,departure aircraft must be asked if ready for immediate...

[ericliu]

Another question, according to ICAO, a landing aircraft cann't be directed to cross the threshold of the runway until the preceding departure one has crossed the end of runway. How to apply this rule?

[BigBoeing]

Thats what we are paid for, its basically down to judgement and experience of a/c types, wind, how confident the pilot sounds etc. And as mentioned some units don't have to worry about this as there are local procedures which allow, when certain criteria/distances are met, two a/c to be on the runway at the same time.

[SINGAPURCANAC]

according to ICAO, a landing aircraft cann't be directed to cross the threshold of the runway until the preceding departure one has crossed the end of runway. How to apply this rule?
The version of doc. 4444 that was available last year,when I prepared something:E,
had such possibilities.
I can't now give you more precise answer but glimpse at new version of document and you will see it. also it is clear stated that such procedures(reduced separation between dep/arr and other combinations) must be approved by appropriate ATS authority .
Practically it means there is no reduction in separation in many countries around the world. As you may know DCAs and similar institutions aren't usually informed about problems and possibly solutions :ugh:
Also I believe that set of technical devices should be employed for such procedures and that means:new procedures,tenders,corruptions, approvals....:=
It wouldn't work....

[Spitoon]

Don't get confused between IFR separation (e.g. reduced separation in the vicinity of an aerodrome) and what might be called general aerodrome control, which is not quite so clearly defined.

As to the original question - local procedures may refine any rules of thumb, but the tower controller should not line up a departure unless there is sufficient time to get it away (and, technically, past the upwind end of the runway) before the inbound reaches the landing threshold. Amongst the other factors already mentioned that will affect the minimum range of the inbound I would include the location and distance from the runway of the holding point. And then add a bit for comfort incase the inbound goes around.

But as BigBoeing points out, it's largely what a controller gets paid for.

If the inbound goes around, technically it's essentially an Approach problem! Having said that, use of a reduced separation in the vicinity of the aerodrome may become very useful in such circumstances - which is why the decision whether or not there is room to get a departure away is affected by weather.

On the second question - just as you have to judge whether there is room to get the departure airborne before the inbound gets to the runway you can add a bit to let the departure get past the upwind end too. In practice though, certainly at busy airports, it seems common practice to be happy if the wheels of the departure are off the ground by the time the inbound crosses the threshold. But this means that there always has to be a plan for the go around!

[criss]

One mile <> one mile, you have to watch for speed on final. Also scenarios are different depending on a/c types - as Spitoon says, usually you're happy with the departing one getting its wheels up, so surely you have to judge how long a given a/c type takes to start its roll, how long will it go down the runway etc. Also, if the arriving a/c is slower (e.g. 737 departing, ATR arriving), a possible go around scenario gets easier, as it has small chance of catching up with the preceeding.

And, if we're talking about speeds, then wind comes into consideration. I did line up and depart an a/c with 767 on 2 miles, but it was doing 80kts GS due to headwind:}

[yarrayarra]

If the inbound goes around, technically it's essentially an Approach problem!

I beg to differ but if there's a go-around the tower controller has blown it and has to ensure that there is either:
- visual separation between the departing aircraft and the one going around or
- a continuing radar separation standard or
--in a non radar environment a procedural standard can be established ie the aircraft departing has left a level on climb such that there is an available level for the aircraft going around to be assigned

[Jat Jet]

The DOC4444, clearly states as per 7 10.1 Separation of landing aircraft and preceding landing and departing aircraft using the same runway
]Except as provided in 7.11 and Chapter 5, Section 5.8, a landing aircraft will not normally be permitted to cross the runway threshold on its final approach until the preceding departing aircraft has crossed the end of the runway-in-use, or has started a turn, or until all preceding landing aircraft are clear of the runway-in-use[/I][/B]
It depends on your skill and experience how far can you go.

[criss]

As long as you don't have two a/c wheels on the rwy at the same time, you're ok.

[ericliu]

Can you get an departure A/C wheels off the ground while an landing A/C just crossing the threshold of the runway? If you do so, it turns out that you must have issued "cleared to land" to the landing one when the departure one was just on the runway, as i know, you can't issue landing clearance until the runway is clear of any traffic, and you also can't issue landing clearance as late as 2 miles from threshold, so the key point is when to issue landing clearance so that the minimum separation between depture A/C and landing A/C can be met.

[yarrayarra]

There is a separation standard to be applied- check your Manual.
How that separation standard is accomplished is based on numerous factors which will determine the "runway occupany time" of the departing aircraft.
- the aircraft types concerned (speed down final and departing clias
- aircraft weight (long haul etc)
- the weather conditions (headwind, cloud base, visibility)
Taking all these into account, not only is the prescribed separation standard required at the moment of takeoff/landing of the two aircraft but the ADC must ensure that, in the event of a go around, a separation standard can be applied
eg firing a C182 with a lear on a 3 mile final might be OK in VMC because, not only will you have the prescribed standard when the Lear touches down but the C182 should be far enough out that in the event of the Lear going around instuctions can be issued to maintain visual separation. Try this in IMC and immediately the Lear has nowhere to go and the controller can't maintain separation ie
- can't maintain visual separation
- won't have 3nm radar separation (or may have but very quickly won't have)
- in a non radar environment the C182 won't be through a level which would give you an IMC assignable level to the Lear

In a nutshell then you can clear the departing aircraft for takeoff any time you like- there is no absolute cut-off. What comes with training is the judgement to know, taking into account the factors above, that the departing aircraft will land with the appropriate runway separation standard and that, in the event of a go-around, you'll be able to apply another standard between the two.

I might be teaching people how to suck eggs here, just that the original question seems to be fairly basic and I'm trying to give a fairly basic answer.

[Spitoon]

Interestng response, yarra. Do you really have prescriberd separations in Oz? It may just be semantics but in the UK the books talk about separation between IFR flights and spacing for other requirements - although the only ones that come to mind are wake vortex. I mentioned earlier in this thread that 'general aerodrome control' is not well defined. ICAO Doc 4444 says 7.1.1.1 Aerodrome control towers shall issue information and clearances to aircraft under their control to achieve a safe, orderly and expeditious flow of air traffic on and in the vicinity of an aerodrome with the object of preventing collision(s) between:
a) aircraft flying within the designated area of responsibility of the control tower, including the aerodrome traffic circuits;
b) aircraft operating on the manoeuvring area;
c) aircraft landing and taking off;
d) aircraft and vehicles operating on the manoeuvring area;
e) aircraft on the manoeuvring area and obstructions on that area.
No mention of separation - just keeping it safe, orderly and expeditious. How the controller does that is largely a judgement thing.

To set out minimum requirements for all aircraft/flights seems to take half the fun out of it!

ericliu, in the UK, except in LVOs, the distance from touchdown by which a landing clearance should be issued is usually guidance. In the extreme case, as long as the clearance is issued before the wheels touch down all is OK. Of course, in normal operations landing clearances are issued before that but, again, it's a judgement thing.

[criss]

you also can't issue landing clearance as late as 2 miles from threshold EKHM?:eek:

Yarra, in procedural control you won't have separation even if its lear departing cessna landing...

[ericliu]

In the case other than reduced runway separation, twr can't issue landing clearance to the arriving A/C until the preceding departure one has lift off the ground, but what if the gap is too tight, the landing pilot decided to go around for the absent of landing clearance, what do you do to deal with this situation?

[Spitoon]

... what if the gap is too tight, the landing pilot decided to go around for the absent of landing clearance, what do you do to deal with this situation?Put plan B into operation.....and fast. Whenever you are controlling you have to have a way to handle things not going as you expected - in the case of arriving aircraft, always know what you will do if it goes around.

As to what to do. Well, if the weather is nice and you can tell one to turn left and the other to turn right and separate them visually it's not too much of a problem - assuming they're not one above the other! In poorer weather when you can't do visual separation you may need to co-ordinate something with approach (remember, plan ahead) in case it happens. Pass traffic information to both the aircraft so that the pilots know as much as possible about the intentions of the other - again, do it when it's begining to look like it's not going to work, not as the aircraft goes around.

But most of all, don't get into that situation. Make a decision in good time - don't let it run on until you are no longer controlling events. Easy to say, and even with years of experience you can get suckered in! But as soon as you start feeling uncomfortable be ready to use plan B.

[criss]

Whenever you are controlling you have to have a way to handle things not going as you expected - in the case of arriving aircraft, always know what you will do if it goes around.

[...]

But most of all, don't get into that situation.

Exactly. ATC is not about resolving 2 a/c head-on 100m apart scenarios ;). BTW - at my place the aviation authority suggested training in re-establishing separation after it was lost. Management decided its not a good idea, as it would teach ATCo's how to circumvent separation minima:}

Situation from today - single runway ops, Ajet lining up with Bjet and Cjet on final. Cld for take-off (immediate), steady after 40 secs, Bjet too close, cancelled take-off and go around. Bjet turned early to allow Ajet to depart on rwy hdg before Cjet, but Ajet now deciding he needs 1 minute to prepare his departure after reclearance:sad:, and Cjet also going around... So, to reiterate - do not line up if NOT ready (almost fully does not fit here :ugh:).

[yarrayarra]

Yep- we have them. I thought everyone did??

Australian MATS:

Runway Separation Standards -
Take-off
10-55-410
Behind a preceding departing aircraft
Apply the 'take-off behind a preceding departing aircraft' standard to fixed wing aircraft, provided that you do not permit a departing aircraft to commence take-off unless the preceding departing aircraft:
a. has crossed the up-wind end of the runway-in-use; or
b. has commenced a turn; or
c. is airborne and has reached a point at least 1800 M (6000 FT) ahead of the following aircraft, provided the runway is longer than 1800 M (6000 FT) and the distance can be readily determined; or
d. is airborne and has reached a point at least 600 M (2000 FT) ahead of the following aircraft provided the :
1. preceding aircraft has an MTOW of 7000 KG or less
2. following aircraft has an MTOW of less than 2000 KG; and
3. following aircraft is slower than the preceding aircraft; or
e. is airborne and has reached a point at least 600 M (2000 FT) ahead of the following aircraft, provided both aircraft have an MTOW of less than 2000 KG.

Given my example of the Lear Vs C182 it's certainly possible, if the situation is reversed ie C182 on final with the Lear to go, that, in the event of the C182 going around, there would be a procedural separation standard available. Given the performance of the Lear there's a good chance it would be through A040 quickly enough to give you A030 for the C182. In a radar environment the speed differential would probably give you your required 3nm separation.
Once again the controller's judgement determines the timing of when the departing aircraft is cleared for take-off. This is where appropriate training and experience is all part of not boxing yourself into a corner with no way out. After all there's normally an easy way and a hard way to do it. Hopefully you can have a long and happy career by doing it the easy way.

[criss]

Yarra, maybe its different down there, but what about ICAO 4444's point 5.7.1? There's nothing about a/c types there.

[Jat Jet]

Landing clearance may be issued if it the prescribed minimum is achieved. Although this a highly debated point in most of the countries except USA, landing clearances is issued only when runway is vacant and available for landing. In States they give landing clearance to no 3 landing aircraft.
:cool:If situation is tight pass on traffic information to landing aircraft, hold your breadth and give landing clearance. 99% cases aircraft will land safely, although flight crew would like to :( kill you. After that prey to Him and try to forget and not to repeat the mistake

[Tarq57]

In NZ we have a similar rule to Australia's re: runway distances/spacing required.
In addition, the condition for landing is that a preceding departing aircraft has lifted off, and is past the point along the runway that the landing type could normally be expected to stop by.
So wheels off, and past a certain point, conditional landing clearance can be issued.
The spacing required between successive arrivals is fairly standard, but relaxes somewhat in the case of light aircraft, where it is perfectly legal to have two light aircraft (or more) occupying the runway at one during landing, provided there is enough space between them that there is no risk of collision. (This suggests fairly good judgement and awareness/perception of a/c performance is advisable.)
The applicable separation requirements/techniques in the case of an overshooting aircraft vs a departure ahead depends very much on weather, flight rules, and local procedures in each case, and although associated with runway separation standards, is a different subject.

[yarrayarra]

Criss- yep understand what you're saying. My understanding is that at any time a controller should be able to prove a separation standard exists. All I'm following up here is more of the techniques type scenario where a controller is setting things up to maintain, what is a big thing here in OZ, "separation assurance" ie if I fall over dead at the console will everything continue to be separated? I'm taking it that one step further here by making allowance for the possibility of a missed approach / go around. Now if a controller wants to just keep blindly firing aircraft without any thought as to the ramifications if it goes wrong then fine, but I just don't know what your defence is when the judge asks you why you didn't make allowance for the B747 which, in the go-around, collected the C182 at the upwind end of the runway and hence a smouldering heap of metal!
Sometimes we just have to stand back and, regardless of how we MIGHT interpret our manuals and standards, have a think about what we're trying to achieve and the safest and most expedient way to do it within the boundaries of those rules.

[ericliu]

Tarq 57
In what condition you could issue a conditional landing clearance, and can you take an example?
Thanks.

[criss]

yarra, you misunderstood me. As a TWR controller I would never debate the issue with the scenario you're providing, its obvious. What I'm saying is that the rule from 4444 I quouted would not allow you to depart a lear in front of a cessna (in procedural control). That's all.

BTW, 747 would be well above cessna at upwind leg :E

[Tarq57]

Tarq 57
In what condition you could issue a conditional landing clearance, and can you take an example?
Thanks.
I don't have the MATS in front of me, but, basically, by day, when the visibility is >5000M, a conditional landing clearance may be issued prior to the required runway separation existing provided there is a reasonable assurance it will exist at the time the landing aircraft crosses the threshold.
An example might be the case of an aircraft just landed, commencing the turn off the runway. The next aircraft is at one mile final. It will take approx 20 seconds for the landed aircraft to finish vacating the runway. You can then say "XXX Boeing vacating runway left, cleared to land."

Caveat.
If the vacating aircraft has a problem and stops still infringing the runway, the pilot of the landing aircraft should notice this and overshoot, but I see it as also the tower controllers' responsibility to cancel his landing clearance if this happens.

[Jimmah]

Tarq57: Not bad with no MATS!

Also, in reference to the original post, we'd be issuing a qualified landing clearance in anticipation of having reduced runway separation (departing a/c airborne beyond expected landing roll), which in itself has a bunch of requirements (mostly the same but also stuff about braking action and controller having reference points for judging distance).

This reduced runway sep stuff is particular to each country's ICAO differences (it's my understanding us Kiwi's are pretty lucky with the ones we have). The qualified take-off/landing clearances are, if memory serves me right, ICAO standard...

I like the only one set of wheels on RWY at the same time method! I have to make the above work with Cherokees on a 2200m rwy!

[yarrayarra]

Criss:
I must be missing something here but I can't understand how you CAN'T fire a Lear for take-off with a C182 on final!!

Don't want to start a tit-for-tat here but what I'd like to know is by what standard you were able to play vertical separation with the B747 on the go- around with the C182 being stepped up underneath?? ie a leap-frog manoeuvre?? I can see that, given the right circumstances, the B747 will outclimb the C182 but how the heck to you say you had established a separation standard. The question here is whether we're wanting to make them miss (which is probably pretty easy after all natural scatter and airmanship does it most of the time) or we're actually applying and achieving a prescribed separation standard.

Maybe we're getting a bit too technical with the possibilities / probabilities / scenarious instead of sticking to the original question which I perceived as fairly simple and straightforward.

Eric- I hope you have been able to gain something from all the answers posted. Just goes to show how controllers can easily get tied up with the "paralysis of analysis sometimes" in their discussions- it really isn't as hard as it seems

Over & out

[criss]

Geez, I said I'm not discussing the scenario with 747 going around against cessna departing, the bit with 747 outclimbing the cessna was only a joke...

ICAO DOC 4444 5.7.1. says:

1. If the arriving a/c makes a full instrument approach, a departure can be released:

a) In any direction up to the point when the arriving a/c commences procedure or base turn

b) In direction differing by at least 45 deg from the direction opposite to final, if the arriving a/c has more than 3 minutes to the threshold

2. If the arriving a/c makes a straight-in approach, a departure can be released:

a) In any direction - at least 5 minutes before the arriving a/c reaches the threshold

b) In direction differing by at least 45 deg from the direction opposite to final - 3 minutes before the arriving a/c reaches the threshold, or before it passes a designated fix

I don't think it will let you release Lear with cessna on 3 miles - unless you have this fix from point 2b at 2 miles, or cessna is doing 40kts, or you're not applying this rule.

[Tarq57]

Not to want to take away from this discussion, but I think the OP was probably asking about runway separations and how to judge them/ any procedures applicable.

The discussion concerning missed approach aircraft and how to separate them falls under the umbrella of approach control - some procedures belonging to approach may be delegated to aerodrome, and are at my unit - but I think it's necessary to be clear as to the difference, even though that difference often overlaps.

[yarrayarra]

Tarq. Yep understand. It's just that in answering the original question the factors as previosly discussed have to be taken into account. If it goes pear shaped then the radar contoller isn't going to be too happy with the ADC for handing him two aircraft with no separation between them. The ADC can't just wipe his hands of it and so "over to you Blue Leader"
If this wasn't a consideration then all the ADC would have to do is fire them as fast as he could regardless of aircraft type and leave it to the radar controller to clean up the mess. And yes I know in a radar environment there are tools (SIDs / radar departures) to help segregate and provide some separation between successive departures of differing aircraft types on tyhe same or similar routes, but I'm talking, once again, in the simplest terms to try and answer a simple question

[Pera]

Criss,

The delays that your quote indicates would be unacceptable at any modern aerodrome.

There are two different ideas being discussed here. You require runway separation in order to launch an aircraft, but you also require some protection against the landing aircraft making a missed approach.

Your quote is referring to protection against missed approaches, but it is very restrictive and I'd say it's referring to procedural control where the tower controller does not have the arrival in sight. Good visibility and/or a radar can change the equation considerably.

Pera

[criss]

Pera

If you take your time to read the thread, you will clearly see I was referring to procedural control.

[Pera]

I was referring to procedural control.

So I was correct. Thanks. :)

A report of 5 DME would be the cutoff (in OZ) for a departure until the tower had the landing aircraft sighted. Even if the Cessna was at 1nm when the tower sighted it, the Lear would still get away. 3 DME in a radar enviroment.