Clearances versus separation
 

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

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.

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.

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

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

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.

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!

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

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.

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.

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

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

Pera

If you take your time to read the thread, you will clearly see 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.