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-   -   Lateral Seperation NAT MNPS/HLA 25nm? RLATSM (https://www.pprune.org/tech-log/575283-lateral-seperation-nat-mnps-hla-25nm-rlatsm.html)

sefaketen 25th Feb 2016 12:59

Lateral Seperation NAT MNPS/HLA 25nm? RLATSM
Hello everybody,
There is a question that i can't find an answer.I have just started to 777 from 737 and reading documents about NAT.
So new procedure called as "RLATSM" is in use for some of the OTS. And it says that lateral seperation is now reduced to 25nm between core tracks of OTS's for specific levels. The question is, how come the 1/2 degrees of latitudes become 25nm instead of 30nms? i think SLOP has nothing to do with it.

DOC 007 says that

In Section 1.10 – “Trials and Future Developments”, information is provided on the planned first phase of North Atlantic trials of reducing the lateral separation minimum to 25 NM. This is scheduled to commence in November 2015. In this “RLatSM” Phase 1, 25 NM lateral separation will be implemented by establishing ½ degree spacing between two specified core OTS tracks, for use by RNP4 Approved aircraft logged-on for ADS-C & CPDLC within the vertical limits applicable to the airspace associated with the NAT Region Data Link Mandate.

Which part i have been missing or wrong?

Thanks in advance.

andmus 25th Feb 2016 14:53

and what about the in-flight contingency procedure in RlatSM.????

BBK 25th Feb 2016 15:29


I don't have the document to hand but I think it's to do with where the tracks "slope" that is where they are inclined. I wondered the same thing re 25 vs 30 nm separation.


Re contingency a subject of much discussion currently. As I understand it turnbacks prior to getting approval need to be out of MNPS airspace. My take on that is below FL280 so down to FL275. I'm not sure if the appropriate ICAO doc is up to date. If anyone has a link please put it up here.


Peter G-W 25th Feb 2016 15:31

Whilst the North-South separation is indeed 30 nm, the actual lateral spacing will be less than that depending on the angle of the track. Given the normal angles of the NAT tracks, they will always be a minimum of 25 nm apart. If they said 30, then someone here would probably complain that it wasn't.


sefaketen 25th Feb 2016 20:18

Peter G-W
Thanks for the reply.

I just can't get it, i mean at which latitude/longitude, ½ degrees latitude distance can be low as 25NMs?

i.e. yesterday tracks were :

T 58/50 58/40 57/30 57/20
U 57/50 57/40 56/30 56/20
V 56/50 56/40 55/30 55/20
W 55/50 55/40 54/30 54/20

For the numbers above; it is all 60NMs we know.And for ½ degree's, it is all 30NMs for the 50ish longtitudes. OTS tracks are all for west-east bounds

Sorry, think i should go back to Geo classes in high school :bored:

As far as i know , the idea is to be offset 15NMs and 500FT descent or climb to a level different than normals.
If you can maintain your altitude, keep it until 10NMs offset, then descent 500FT below or above, then make it 15NMs offset.
If you can't maintain the altitude, with the possible lowest rate of descent,be offset from track, when clear of traffics and tracks, expedite descent to 500FT above or below of desired flight level

At 15NMs offset, go below FL280, then divert.

Cough 25th Feb 2016 21:33

If the tracks run perfectly E-W then 30nm is assured. But they don't. Taken to extreme, if the tracks run N-S then the spacing is 0nm! But for an average track that jinks a little norther south, thats enough to bring the 30 down so something approaching 25nm. Thats where it comes from.

But at the moment the track message contains...

So there aren't any RLatSM tracks.

sefaketen 26th Feb 2016 14:54

I think i understood now. My mistake is that i always think OTS runs perfectly E-W.So when they tend to be N-S , it may reduce below 30NMs.

Thanks for the info @Cough

Trimaranus 11th Oct 2016 13:37

this is the last version of the NAT manual.
In effect it seems there is no change in the contingency procedures chapter regarding the RLAT. probably because it s considered safer to stay 15 NM out of the track, where the possibility that another aircraft in an adiacent track is experiencing a similar emergency, than flying closer to the own track where there may be more traffic and more risk of proximity.

Spooky 2 12th Oct 2016 10:50

Suggest you Google, and down load the North Atlantic Resource Guide. It is for US operators, but it still is ICAO driven and compliant. Revised every 90 days so it's the most current document out there. Also AC91-70B is good resource. Don't let the FAA stamp of approval drive you off we are all working in the same airspace.

EPR turbo 9th Nov 2016 09:12

Does anybody know when the trail phase for the RLatSM ends? Meaning, when you need to be RLatSM approved by local authority in order to continue to have access to the NAT HLA track system?
Thanks for info and links

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