lateral separation in DOC4444
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lateral separation in DOC4444
I am quite confused by the lateral separation in 4444 5.4.1.2 " VOR: both aircraft are established on radials diverging by at least 15 degrees and at least one aircraft is at a distance of 28 km (15 NM) or more from the facility".
Questions are:
1. It doesn't say whether the two aircraft are converging or diverging or even opposite direction, so does it mean it applies to all the scenarios?
2. Supposing the critical condition, one aircraft is right 15nm from the vor, the shortest lateral distance between this one and another one which is on the other radial could be around 7km, it's much less than the minmum radar separation 10km. In practice, most controllers dare not use this rule to separate the aircraft in procedural control. The procedual separation shall be much larger than radar separation, shalln't it? But it happens in this rule.
Any information would be appreaciated!
Questions are:
1. It doesn't say whether the two aircraft are converging or diverging or even opposite direction, so does it mean it applies to all the scenarios?
2. Supposing the critical condition, one aircraft is right 15nm from the vor, the shortest lateral distance between this one and another one which is on the other radial could be around 7km, it's much less than the minmum radar separation 10km. In practice, most controllers dare not use this rule to separate the aircraft in procedural control. The procedual separation shall be much larger than radar separation, shalln't it? But it happens in this rule.
Any information would be appreaciated!
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An interesting question that I recall discussing over the years. The text in PANS-ATM doesn't say which way the aircraft are going but the picture shows both going away from the fix, and the text talks about the radials diverging which again suggests that it may require the aircraft to be diverging too. But it's ambiguous.
In practice, aircraft are either separated by a particular separation standard or they are not - the controller's job is to make sure that at least one of the separation standards is in place between two aircraft at all times. So, in the worst case when the two aircraft are inbound to the VOR, when the second is less than 15 miles away they are not separated laterally and you have to have vertical separation established. So you might use a clearance like "climb FL 350 to be level 15 DME before ABC".
Separation standards are based on the accuracy of the navigation systems being used (amongst other things). I guess that close to the VOR the position of the aircraft is very accurately known and so a small, but accurate, separation is 'acceptable'. You might be surprised at the inaccuracies that can exist in the radar picture you see! Separations are calculated on the statistical probability that the aircraft will be a specific distance apart. There is no reason that a procedural separation has to be more than a radar separation if the mathematics works out.
I can understand why you feel uncomforatable using this separation. In which case, don't use it - the controller is in charge!
In practice, aircraft are either separated by a particular separation standard or they are not - the controller's job is to make sure that at least one of the separation standards is in place between two aircraft at all times. So, in the worst case when the two aircraft are inbound to the VOR, when the second is less than 15 miles away they are not separated laterally and you have to have vertical separation established. So you might use a clearance like "climb FL 350 to be level 15 DME before ABC".
Separation standards are based on the accuracy of the navigation systems being used (amongst other things). I guess that close to the VOR the position of the aircraft is very accurately known and so a small, but accurate, separation is 'acceptable'. You might be surprised at the inaccuracies that can exist in the radar picture you see! Separations are calculated on the statistical probability that the aircraft will be a specific distance apart. There is no reason that a procedural separation has to be more than a radar separation if the mathematics works out.
I can understand why you feel uncomforatable using this separation. In which case, don't use it - the controller is in charge!
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In the past I used this separation on a daily basis;
1. It can be used in all scenarios - both acft inbound, both acft outbound or one each way.
2. Procedural and radar separation standards are usually based on a buffer of 1 NM and then adding the inaccuracies of the equipment being used - nav tolerance for nav aids, or the accuracy of the radar system. This results in some procedural separations being smaller than the standard radar separation.
1. It can be used in all scenarios - both acft inbound, both acft outbound or one each way.
2. Procedural and radar separation standards are usually based on a buffer of 1 NM and then adding the inaccuracies of the equipment being used - nav tolerance for nav aids, or the accuracy of the radar system. This results in some procedural separations being smaller than the standard radar separation.
jaws is right - the procedural standard can mean aircraft are closer together than the radar standard.
As long as aircraft are established on the radial then it doesn't matter which direction either of them is going.
A & B inbound - assign B 6000 and A has requirement to reach 5000 by lateral separation point
A & B outbound - assign B a separated level under the level A has left. Once the first aircraft reaches lat sep pt, B can have unrestricted climb.
A inbound, B outbound - assign B 6000, assign A 5000. Once A reaches lat sep pt they can both have unrestricted climb/descent.
The trick to all the above is to pick appropriate levels based on distance of both aircraft and performance of the aircraft.
As long as aircraft are established on the radial then it doesn't matter which direction either of them is going.
A & B inbound - assign B 6000 and A has requirement to reach 5000 by lateral separation point
A & B outbound - assign B a separated level under the level A has left. Once the first aircraft reaches lat sep pt, B can have unrestricted climb.
A inbound, B outbound - assign B 6000, assign A 5000. Once A reaches lat sep pt they can both have unrestricted climb/descent.
The trick to all the above is to pick appropriate levels based on distance of both aircraft and performance of the aircraft.
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A few more
VOR: Separation is established when both aircraft have reported established on radials which diverge by 60 degrees or more.
NDB: Separation is established when both aircraft report established on tracks which diverge by 90 degrees or more.
Assuming both aircraft fly over the VOR/NDB at exactly the same time and report established on radials/tracks soon after, one can have a whole lot less than any minimum radar separation.
P
NDB: Separation is established when both aircraft report established on tracks which diverge by 90 degrees or more.
Assuming both aircraft fly over the VOR/NDB at exactly the same time and report established on radials/tracks soon after, one can have a whole lot less than any minimum radar separation.
P
Last edited by porra; 15th May 2009 at 10:24.
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Ericliu. Are you, or have you been, a controller? You state in other posts that you are an instructor. Where? How is it possible that you can have such huge gaps in your understanding of air traffic control, and be an instructor?
Furthermore, if you are an instructor (!), why would you be attempting to fill your knowledge gaps via pprune? You have absolutely no way of knowing the quality of any information derived here.
Furthermore, if you are an instructor (!), why would you be attempting to fill your knowledge gaps via pprune? You have absolutely no way of knowing the quality of any information derived here.
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And if the procedural separation is smaller than the radar, how would you say it's safe enough?
5.6.1 One-minute separation is required if aircraft are to fly on tracks diverging by at least 45 degrees immediately
after take-off so that lateral separation is provided (see Figure 5-35).
This is often way less than the 3/5nm separation used between departures, especially between slow aircraft, still not unsafe by any means.
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I understand the one-minute separation is less than the radar separation, and it's used quite safely. My concern is the vor lateral separation which we take great care for the possibility of being a couple of miles away between two aircraft. So in practice, most controllers are confused about that.
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The initial example is for aircraft DIVERGING ONLY. There are other examples for Converging and One In - One out scenarios (at least there is in UK MATS Part 1 which is my BIBLE).
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Hub47
As you move around the world you will find that there are different "Bibles" in different countries. But the initial question was about Doc4444.
Ericliu
Can't remember exactly where I saw the 1NM buffer mentioned, but I will do some research (if I can get my hands on the relevant Doc's).
As you move around the world you will find that there are different "Bibles" in different countries. But the initial question was about Doc4444.
Ericliu
Can't remember exactly where I saw the 1NM buffer mentioned, but I will do some research (if I can get my hands on the relevant Doc's).
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Ericliu- studiously ignoring my questions?
Verci
Really? Why is that? If this person is, as claimed, an instructor, why would he seek answers here when he has no idea of the quality of the responses? Surely it would be better to seek answers from ICAO or having his ANSP seek appropriate expertise? Seems a little unprofessional to be filling knowledge gaps by asking questions on an anonymous internet forum. Lets face it, there are people on here claiming to be "consultants", when in fact they are unemployed ex-management failures who were dismissed from their jobs due to incompetence. Would you take advice from this sort of self-delusional idiot?
Verci
it would be better if you would enlighten him,
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Thank you AirNoServicesAustralia for your explaination. Actually, I understand how to apply this separation in procedural control. What I want to find out is the basis that the lateral separation can be used very safely although it might be less than radar separation some time. Many controllers in my unit are discussing about the risk of this separation. So we seldom use that when the two aircraft are lateral close although one of them is around 30 km apart from the VOR for the fear of less than radar separation.
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procedural sep
Not just off VORs...you can use (back in OZ) 1nm north or south of the centreline, while the other one is the other side, 1nm either side of the coast etc.
The best one to use is the visually sight and pass...in some parts of Europe they have to wait until the aircraft have passed by the full radar standard for opposite direction traffic. In Oceanic Control Areas and other CTAs (outside of Europe) as soon as they both say they have passed, up or down they go! (Lots of others also use "green between" for definite passing using radar, but that is another issue).
I am with Ferris and ANSA regarding the veracity of information here...it's like Wikipedia in some respects.
The best one to use is the visually sight and pass...in some parts of Europe they have to wait until the aircraft have passed by the full radar standard for opposite direction traffic. In Oceanic Control Areas and other CTAs (outside of Europe) as soon as they both say they have passed, up or down they go! (Lots of others also use "green between" for definite passing using radar, but that is another issue).
I am with Ferris and ANSA regarding the veracity of information here...it's like Wikipedia in some respects.
DOC 4444
para 5.4.1.1.1 Lateral separation shall be applied so that the distance between those portions of the intended routes for which the aircraft are to be laterally separated is never less than an established distance to account for navigational inaccuracies plus a specified buffer. This buffer shall be determined by the appropriate authority...
Note: In the minima specified in 5.4.1.2, an appropriate buffer has already been included.
In Australia, our lateral separation requirement is 1NM (the appropriate buffer) between the possible position of 2 aircraft - so apply the navigation tolerances of both aircraft and as long as there is 1NM between the tolerances they are separated. If you are using radials, the point where the gap between the tolerances reduces to 1NM is the lat sep point - you must establish another standard before 2 aircraft can be inside this point. It is quite easy using this standard to have aircraft closer together than the radar standard and this is regularly done at procedural towers around Australia.
ericliu: the note attached to 5.4.1.1 says the buffer is already included in 5.4.1.2.
5.4.1.2 has no restriction on direction of travel.
Nowhere in doc 4444 does it say that procedural separation has to have aircraft further apart than radar separation. In fact, you have shown that procedural can be less than radar and this is used regularly at many places around the world.
For those that want to refer to doc4444, here is a Danish link (it's in English)
http://dcaa.slv.dk
000/icaodocs/
The link still works despite colon 8 being turned into a Nerd smilie.
para 5.4.1.1.1 Lateral separation shall be applied so that the distance between those portions of the intended routes for which the aircraft are to be laterally separated is never less than an established distance to account for navigational inaccuracies plus a specified buffer. This buffer shall be determined by the appropriate authority...
Note: In the minima specified in 5.4.1.2, an appropriate buffer has already been included.
In Australia, our lateral separation requirement is 1NM (the appropriate buffer) between the possible position of 2 aircraft - so apply the navigation tolerances of both aircraft and as long as there is 1NM between the tolerances they are separated. If you are using radials, the point where the gap between the tolerances reduces to 1NM is the lat sep point - you must establish another standard before 2 aircraft can be inside this point. It is quite easy using this standard to have aircraft closer together than the radar standard and this is regularly done at procedural towers around Australia.
ericliu: the note attached to 5.4.1.1 says the buffer is already included in 5.4.1.2.
5.4.1.2 has no restriction on direction of travel.
Nowhere in doc 4444 does it say that procedural separation has to have aircraft further apart than radar separation. In fact, you have shown that procedural can be less than radar and this is used regularly at many places around the world.
For those that want to refer to doc4444, here is a Danish link (it's in English)
http://dcaa.slv.dk
000/icaodocs/The link still works despite colon 8 being turned into a Nerd smilie.
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In the past I used this separation on a daily basis;
1. It can be used in all scenarios - both acft inbound, both acft outbound or one each way.
1. It can be used in all scenarios - both acft inbound, both acft outbound or one each way.
A is B747 480Kt westbound - 090 radial 15 dme
B is B747 480Kt eastbound - 270 radial 1 dme
They are head on and 1 minute appart.
It would be a brave controller that would be happy to have no vertical separation fully established until they were that close together.
Regards,
DFC
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The 090 radial diverges from the 270 radial by 180 degrees. Way more than the minimum of 15.
Well said. 
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Originally Posted by ferris
Now my point about quality of response is nicely made.