Semi-circular rule - help!

[Brett Davis]

Hi all.

In light of the recent conversation about the quadrantal rule (see http://www.pprune.org/forums/showthread.php?t=217051), I was hoping for a bit of explanation on the finer points of the semi-circular rule.

I'm currently preparing for my final NATS interview and this is in the material but I'm not sure I understand it completely. Essentially the book given to me by NATS to study says the following:

Inside controlled airspace when flying IFR above FL245, the following applies:
Heading 000 - 179 - FL250 is the lowest usable FL, then increments of 4000ft from FL290 @ odd FL's.
Heading 180 - 359 - FL 260 is the lowest usable FL, then increments of 4000ft from FL310 @ even FL's.

It's the second part that gets me; I understand that 4000ft from FL250 is FL290 and then so on. What I dont get is a) why the massive seperation distance of 4000ft when surely 2000ft would suffice to allow minimum seperation while leaving room for opposite direction traffic and b) why do the westboud flights have to jump from FL260 to FL 310 (5000ft when everything else is 4000ft)?

Now I'm suspecting that the reference in my book from NATS about the next westbound FL being FL310 could just be a typo, but I'd like some clarification on this if at all possible.

Many thanks in advance,

B

[camisa10]

As far as i can remember,up to FL290 -vert.separation is 1000' for opposite direction traffic,and 2000' for same direction traffic.
eastbound levels are 250(the lowest ,as you said),270 and 290
westbound levels are 260 and 280.

Above FL290 is (was) "increased" vertical separation ,so now it's 2000' for opposite direction traffic and 4000' for same direction traffic .
eastbound levels are(were) 330,370, 410...etc
westbound levels are (were) 310,350,390,430...etc
regards

[ukatco_535]

unless of course you satisfy the MNPS and are in RVSM airspace!!

[Chilli Monster]

All European Airspace is now RVSM airspace - so you can forget the change in separation above FL290. It's 1000ft apart all the way up.

Also - It's magnetic TRACK - not Heading (Heading is where the aircraft is pointing, but with a strong crosswind it's track across the ground will be different).

So - Magnetic Track 000-179: FL 70, 90, 110................270, 290, 310, 330 etc.

180-359: FL60, 80, 100................ 260, 280, 300, 320 etc

[MancBoy]

Not quite right chilli.

RVSM airspace ends at 410 then its 2000 feet separation above that so 430 is eastbound and 450 is westbound etc

[Chilli Monster]

I knew it stopped somewhere - just couldn't remember where above 400 it did. Ta! (Never work that high anyway ;) )

[MancBoy]

Until recent years you rarely spoke to stuff above 400 but now its pretty common to have to separate loads of stuff at 430

I've even spoken to the JCB gulfstream at 530 which must have been some view from the flight deck!

[eyeinthesky]

Even better:

A G5 en route from Moscow to the Caribbean which entered London Airspace at FL550. When asked, he said his planned time en route was 13 hours, and when he got there he would still have an hour's flying fuel left with reserves! :cool:

Edited to say: The semi-circular rules do not ALWAYS follow convention: South of ORTAC Brest Control use conventionally Eastbound levels (330, 350,370 etc) for Westbound (= Southbound) traffic due to conflicts with crossing traffic over the Brest peninsular.

In addition, the core Oceanic tracks use every level to maximise capacity. There is no opposite direction traffic on the core tracks so they can all go at 290,300,310,320,330 etc

[Pierre Argh]

just to chip in six'pen'orth... ISTR the reason why the separation above F290 was increased was because of inaccuracy in old-fashioned clockwork altimeters... newer equipment (coupled with an imperative to squeeze more aircraft in) hence Reduced Vertical Separation Minima (RVSM) and the separation can be reduced?

[ukatco_535]

Bonjour Pierre

Or should that be 'allroight moy luvverrr'

I believe you are correct - airspace 'pressure' and better equipment. 'sfunny how the accuracy of altimeteres has suddenly improved!!

[bookworm]

In light of the recent conversation about the quadrantal rule, I was hoping for a bit of explanation on the finer points of the semi-circular rule.
I'm currently preparing for my final NATS interview and this is in the material but I'm not sure I understand it completely. Essentially the book given to me by NATS to study says the following:
The "semi-circular rule" as it stands in law is part of Rule 30 of the Rules of the Air. It applies outside controlled airspace about FL245. Given that the UK has no uncontrolled airspace above FL245, it's somewhat pointless.
Of course the conventions in the semi-circular rule are used for IFR flight in controlled airspace at all levels, according to MATS Part 1. But you might score trivia points with your interviewer for that particular "finer point".

[songbird29]

Better accuracy of altitude measuring equipment and pressure to increase capacity, that's the story and I think by itself there is nothing wrong with it.
But I have a question on turbulence.
Is turbulence behind heavy aircraft, with a tendency to slowly drop but staying persistent for quite a few minutes, a problem for the lighther categories of aircraft flying thousand feet below on the same precision track?
The expected advent of light jets able to fly up till FL410 may aggravate the problem.
What does one think?

[BA Baracus]

Just when you thought this one had been put to bed......

Just out of mere curiosity more than anything else and taking onboard all the previous posts:

Would I be right in saying that...... where RVSM ends (ie FL410) - this last RVSM FL is eastbound. After that there is 2000ft separation, so the next FL available is FL 430 which is also eastbound and the next westbound FL is 450, then ...FL470 east, FL490 west etc...

This means that between the last RVSM westbound FL 400 and next subsequent westbound level FL450 - there is a difference of 50FL instead of the 40FL separation as in the others above RVSM for each direction?

Westbound...................Eastbound
400
.......................................410

.......................................430
450
.......................................470
490


Also, magnetic track vs headings? Does this mean your aircraft could be pointing in a northerly heading, but due to the wind, it could be tracking an easterley direction (ok very strong winds in that case) in theory?

Thanks

[Chilli Monster]

Also, magnetic track vs headings? Does this mean your aircraft could be pointing in a northerly heading, but due to the wind, it could be tracking an easterley direction (ok very strong winds in that case) in theory?


Yes - see HERE (http://education.qld.gov.au/curriculum/area/maths/compass/html/airnav/aical3.html) for an explanation

[camisa10]

BA Baracus
Nope ,you're wrong.It's always odd level-even level-odd level..etc..that pattern.So ,last RVSM level is FL410 which is an odd FL,next one must be even FL.But now we must apply 2000' for opposite direction traffic -so next even level would be FL 430,than next odd level is FL 450,even 470,odd 490..etc .
regards

[BA Baracus]

Thanks for clearing those up for me!

:ok:

[Brett Davis]

BA Baracus
Nope ,you're wrong.It's always odd level-even level-odd level..etc..that pattern.So ,last RVSM level is FL410 which is an odd FL,next one must be even FL.But now we must apply 2000' for opposite direction traffic -so next even level would be FL 430,than next odd level is FL 450,even 470,odd 490..etc .
regards

Ok call me stupid (stop sniggering), but this is still confusing me. Surely FL's 430 and 470 etc. are odd?

[PPRuNe Radar]

'Odd' and 'even' are confusing 'units' of nomenclature, at least in Upper Airspace (where the Quadrantal does not apply anyway).

It should be simply Westbound and Eastbound really.

Even before RVSM, some Westbound levels were numerically 'Odd' (F310, F350, F390, etc, etc)

[camisa10]

Brett Davis
Ok,have to admit-it is a bit confusing at first but,let's try to simplify it:
-up to FL 290 apply 1000 ft for opposite direction traffic.So eastbound level is 250,westbound 260,e-bound 270,w-bound 280,e-bound 290.
Ok..now we have two possibilities for higher altitudes-RVSM scheme and NON RVSM scheme.

*RVSM scheme:
the same pattern is applied up to FL 410 which is the last eastbound RVSM level,next level is NON RVSM westbound level ,and now 2000 ft vertical separation must be applied.So ,next westbound level is 430,e-bound 450,w-bound 470,e-bound 490...etc

*NON RVSM scheme
above 290 you must apply 2000' for opposite direction traffic.Next westbound level is 310,e-bound 330,..etc
So eastbound levels are : 330,370,410,450,490..
and westbound levels are : 310,350,390,430,470,510...etc
cheers