UN851 - Odd or Even level?

[Lorenzo Stobbione 1368867]

Hi all,

I'm opening this topic because today I flew this route from ABESI to MAKEL with a path which is slightly eastbound.

I was expecting having odd flight levels but, while inside Langen area, I have been asked to fly even flight levels.

No issue about that but this situation arose a question in myself. What is the correct way to plan a flight on a route, like UN851 which goes mostly straight North and has in its path both westbound and eastbound segments?

Do I have to plan a flight level change every time I p[Mod - Happy Thoughts] over heading 360 or is there any waiver to it due to the peculiarity of the route?

 

Thank you in advance for your support!

[Martin Loxbo]

It will be specified in the national AIP what levels to use, precisely so you don't have to change cruising level whenever the track changes slightly.

 

Example from the Swedish AIP: https://www.aro.lfv.se/Editorial/View/2441/ES_ENR_3_3_en

[Randy Tyndall 1087023]

Martin,

 

Looking at the link you posted I just want to be sure I am reading the excerpt correctly.

 

On the L24 if you are flying from MASEV to EVLAN you are flying generally Northbound at an odd flight level, correct? I ask this because the "Arrow" is pointing in a direction that would be "south" on a map, yet the Latitudes given for the way points indicate that EVLAN is located farther north than MASEV. I also [Mod - Happy Thoughts]ume since there is no corresponding "even" arrow this is a one way Airway?

 

What also confuses me is that for the L77 RNAV route, it is the southbound traffic (not north bound as on the L24 RNAV Route) that flies at an odd flight level, if my interpretation of the way to read the info on the page is correct.

 

At a glance, without really looking at the latitudes of the way points, I would "fly" in the direction indicated by the direction the arrow pointed, up or down as the case may be, and that would be wrong, again, if I am interpreting the info correctly.

 

Randy

[Andreas Fuchs]

Hi Randy,

 

in France, Spain and Italy cruising levels are [Mod - Happy Thoughts]igned according to the criteria whether you are on a northbound (even) or on a southbound (odd) magnetic track. The AIP or, easier, IFR enroute charts present this information.

The airways UN850 and UN851 specifically are defined according to the above rule as well, inside Germany. This means that northbound traffic would remain on an even level until reaching the Danish border, then change to odd. The other way around traffic arriving from Denmark would have to change from even levels to odd levels at the border to German airspace (Bremen EDWW/Maastricht EDYY), if continuing on UN850.

[Dace Nicmane]

Do I have to plan a flight level change every time I p[Mod - Happy Thoughts] over heading 360 or is there any waiver to it due to the peculiarity of the route?

The general rule is you don't have to think about every segment of your route. Check the direction from your departure airport direct to your destination airport which in the case of LIMC-ENSB is 002°, so in Italy and Switzerland you have to be on an even level (because they have the North/Southbound rule and you're going North) and plan to change to an odd before you cross into the German airpsace (because 002° is East according to the East/Westbound rule) and let the ATC take care of the rest in case there are some exceptions for some airways.

[Lorenzo Stobbione 1368867]

Thank you for all your answers.

I was using only the semicircular rule to choose flight levels and this was misleading me on northbound flights outside my country (Italy) where the rule is rotated by 90° clockwise.

 

About the specific planning I have been able to follow all the routes using EAD information sources and I have seen that some routes have exceptions, like P600 which goes westbound when crossing the ocean but requires odd flight levels of northbound.

 

I understand that the ACC will take care about separation but I like understand how it works so that I can be already compliant .

 

Thanks a lot!

[Martin Loxbo]

Martin,

 

Looking at the link you posted I just want to be sure I am reading the excerpt correctly.

 

Hi Randy,

 

In the case of L24 the table shows that it is a one-way route going from MASEV to EVLAN at ODD levels only. While EVLAN is slightly further north than MASEV, looking at a chart (https://www.aro.lfv.se/Editorial/View/2447/ES_ENR_6_1-1_en) you can see that the route is eastbound and follows the normal semicircular rule nicely.

[Randy Tyndall 1087023]

Martin,

 

I see what you mean, yet it is only slightly north of MASEV. If it were slightly south the level would be even, yes?

 

To me that doesn't seem to fit with the generalized intent of ICAO, which I if I understand correctly, is predominantly East-West flight level oriented. L24 is far more predominantly east-west than north-south

 

So that begs the question, since ICAO is an international organization, why do specific countries decide to adopt a north-south rule?

 

Don't misunderstand why I am asking the question. I understand national sovereignty and control. Still, there must be a practical reason for the 90 degree change in the flight level altitude guidance. Is it because of an individual country's geographical orientation? Seems the majority of the countries that adopt the north-south guideline (i.e., Italy, Sweden, Portugal, etc) are geographically north-south oriented with little east-west distance between borders/boundaries.

 

Still, to me, that only seems to create the potential to breed confusion among international pilots. Especially in cases like Andreas pointed out where flight levels suddenly change from even to odd or odd to even at international borders.

 

But, given all that, I still make every absolute effort to follow the guidelines country by country, whether under ICAO, or FAA, or NAC, or whatever the controlling authority is. (But I have been known to fly westbound on an eastbound only airway in the USA a time or two... )

 

Randy

[Martin Loxbo]

In Sweden we generally follow the east/west rule, not north/south as in France, Italy, Portugal and Spain. So in the example with the route L24, it would most likely specify odd levels going eastbound even if the direction were slightly different (SE vs NE). You can look at other routes in Sweden and you will see that generally it is the case that eastbound uses odd levels and westbound uses even levels. There are a few exceptions to this, mainly for some routes going to/from the north of Sweden (T314, T317 and M607 to name a few), which have odd levels northbound and even levels southbound. The reason for this is simply that if they would strictly follow the east/west rule you would have level changes whenever the track changes through 360 or 180 degrees, which would be very impractical. You would also have adjacent routes where traffic on more or less opposite tracks might be on the same level. This is why the AIP specifies the cruising level for each individual route.

 

Is it because of an individual country's geographical orientation? Seems the majority of the countries that adopt the north-south guideline (i.e., Italy, Sweden, Portugal, etc) are geographically north-south oriented with little east-west distance between borders/boundaries.

 

That's absolutely correct (except Sweden uses the east/west rule except for certain routes, as mentioned above). For example in Spanish airspace the bulk of the traffic flies between Spain and the Canary Islands and the north of Europe, so it would be impractical to change levels whenever the track changes through north/south.

[David Zhong]

No need for pilot confusion - the Jepp en route charts (and I [Mod - Happy Thoughts]ume competitors like Lido have the same) show how the cruising levels work for each airspace.

[Andreas Fuchs]

Do I have to plan a flight level change every time I p[Mod - Happy Thoughts] over heading 360 or is there any waiver to it due to the peculiarity of the route?

The general rule is you don't have to think about every segment of your route. Check the direction from your departure airport direct to your destination airport which in the case of LIMC-ENSB is 002°, so in Italy and Switzerland you have to be on an even level (because they have the North/Southbound rule and you're going North) and plan to change to an odd before you cross into the German airpsace (because 002° is East according to the East/Westbound rule) and let the ATC take care of the rest in case there are some exceptions for some airways.

As mentioned, some airways in Germany run with the North-EVEN/South-ODD rule, namely UN850/UN851 (and a few others).

[Simon Kelsey]

So that begs the question, since ICAO is an international organization, why do specific countries decide to adopt a north-south rule?

 

Mainly because the airways in those countries are predominantly oriented north-south and therefore it makes far more sense to make the cruising levels north-south rather than either have people (theoretically) changing level frequently or have lots and lots of exceptions to the east-west rule.

[Lorenzo Stobbione 1368867]

No need for pilot confusion - the Jepp en route charts (and I [Mod - Happy Thoughts]ume competitors like Lido have the same) show how the cruising levels work for each airspace.

 

Well, I use Navigraph charts and they normally use an E> or O> marker on some routes..I don't really know if they mean "consider this route as Eastbound" since with UN851 they are not really compliant.. in any case I just discovered eurocontrols EAD services which is really good in combination with them since it lets you have all AIPs at once.

 

Nice!

[Andreas Fuchs]

Hey Lorenzo,

 

I do not have those Navigraph Charts, but Jeppesen charts as I am lucky to get them for free at work. At least on these UN851 is marked as "E" all over Germany until reaching the border to Denmark.

 

Obviously "E>" means "use EVEN levels into the direction of the arrow" and "O>" stands for "use ODD levels into the direction of the arrow".

[Lorenzo Stobbione 1368867]

Hey Lorenzo,

 

I do not have those Navigraph Charts, but Jeppesen charts as I am lucky to get them for free at work. At least on these UN851 is marked as "E" all over Germany until reaching the border to Denmark.

 

Obviously "E>" means "use EVEN levels into the direction of the arrow" and "O>" stands for "use ODD levels into the direction of the arrow".

 

That is the big ah-ha moment:) ... it was under my eyes and I did not recognize it... what can I say.. thank you very much!!

[Andreas Fuchs]

Welcome

 

PS: actually I do enjoy colleagues like you who are genuinely interested and are not shy of asking!

[Lorenzo Stobbione 1368867]

Thank you, I hope to meet you online !