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This question is aimed at Air Traffic Controllers who are familiar with ICAO Separation minima. DOC 4444 states the following:

Lateral separation between two aircraft exists when: 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 (see Figure 5-4) VOR Seperation

Note that i have highlighted the word "diverging". The only example given here is when two aircraft are flying away from the VOR (diverging).

Q#1. In this scenario the VOR is located at the airport. Two aircraft are departing that airport, when the leading aircraft is 15nm or more from the VOR on radial 020, the following aircraft is laterally separated when he flies on radial 035. Is this correct?

Q#2 What if both aircraft are less than 15 nm? How many degrees of separation must there be in that case?

Q#3 What about when one aircraft is flying away from the VOR and the other one is flying towards the VOR? AC1 is flying away from the VOR on R015 and is 20nm from it at FL060 . AC2 is flying towards the VOR on R030 and is at 25NM descending through FL060. Are these two aircraft separated?

Q#4 Same scenario as mentioned above, but AC1 is 10NM from the VOR and AC2 is 20NM from the VOR (same radials and levels as mentioned above). Are they separated?

Q#5 What if both aircraft are flying towards the VOR? AC1 is flying to the VOR on radial 010 maintaining FL200, 30NM from the VOR. AC2 is flying to the VOR and is at FL210 35NM from it on radial 025. Does this mean that since you have at least 15 degrees on the radials, that AC2 could continue its descent through FL200?

Also are there any sites,videos, other manuals or resources that have a better explanation on ICAO separation minima (other than DOC 4444)?

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    $\begingroup$ I'm not familiar with the ICAO doc, but Q1 and Q2 are both answered by the text and picture in your question (at least from what I understand). Q5 is unclear because first you say both aircraft are flying to the VOR, but then you immediately say that AC1 is flying away from it. $\endgroup$ – Pondlife Jul 2 '18 at 17:34
  • $\begingroup$ sorry q5 was a mistake, it is corrected now. $\endgroup$ – user30767 Jul 2 '18 at 20:22
  • $\begingroup$ Q2 is also corrected $\endgroup$ – user30767 Jul 2 '18 at 20:29
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    $\begingroup$ Do NOT destructively edit questions. $\endgroup$ – abelenky Aug 20 at 22:58
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  1. Exactly. As long as the aircraft are diverging (i.e. flying away from the VOR), one of the aircraft is at least 15nm away from the VOR and both are at least 15 degrees (radials) apart, the separation is achieved.
  2. You cannot use VOR separation with less than 15nm distance. The other option that can be used is "geographical separation", ref ICAO Doc 4444 5.4.1.2.1.1.
  3. As they are still more than 15 nm away from the VOR, I would say yes. There would need to be however a certain restriction in place for the inbound aircraft to cross 15 DME (or preferably much before to have some margin) at FL50/5000ft or below, to ensure separation.
  4. Yes. As far as one aircraft is 15nm or more away from the VOR, the separation is ensured. The photo in your question nicely depicts this, as it shows that only one (the furthest) aircraft has to be 15nm or more away from the VOR.
  5. Yes, but you would have to ensure that they are vertically separated before the last inbound aircraft reaches 15nm from the VOR.
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