Flying westbound should be positive FL. Explain please?

[WhySoTough]

I can't seem to remember the whole idea of this as it has been a long time since studying it.
I do remember that flying westbound should be on positive Flight Levels, and odd flight levels for eastbound traffic.
Also, when saying westbound traffic, that is traffic flying magnetic headings between 180-359, is this correct?.. or??

Can somebody please explain this to me, and tell me why this is.
Thanks guys

[G CEXO]

Quadrantal rules: http://www.casey.tgis.co.uk/vatsim/howto/quadv3.pdf

[FlyingSportsman]

You'll be looking for semi-circular, probably not qaudrantal. May have misunderstood your question, but it seems as though you are asking about the Semi-circular or hemispheric (IIRC) rule.

From WIKI : The standard rule defines an East/West track split:

Eastbound - Magnetic Track 000 to 179° - odd thousands (FL 250, 270, etc.)
Westbound - Magnetic Track 180 to 359° - even thousands (FL 260, 280, etc.)
As you'll know (I assume) RVSM begins above FL285 up to FL410 and allows you to fly 1000 feet vertically apart from other traffic. This is signifcant because Semi-circ rules above FL290 increase the gap to 4000', FL290, 330, 370 e.t.c so with the correct equipment you can partake in RVSM.

FS :ok:

[RichardH]

It's all to with procedural air traffic vertical separation. It is based upon magnetic TRACK (not heading).

So if aircraft track is 000 to 179 (east bound) it flies ODD level FLs.
From 180 to 359(west bound) it flies EVEN level FLs. This gives a 1000 ft vertical separation from opposite traffic.

Life gets a bit more complicated when flying above FL290 when a minimum of 2000 ft separation is required. So you can be flying due west at FL280 and your next valid west bound level is FL310 (Yes I know it's an odd number, but it's an EVEN cruising level) - favourite exam question. Odds remain the same FL290, FL330, FL370 but notice 4000 ft in same direction.

The above is the ICAO standard, but please note that in areas of Reduced Vertical Separation Minima (RVSM) Eg. North Atlantic and most of Europe. FL290 to FL410 then as before east is odd and west is now even. So FL360 is a valid west bound FL under RVSM. Remember that most jet's optimum altitude is around FL350 and everybody wants to fly there, hence with more accurate altimeters etc. RVSM allows more traffic down the same tube.

Note that Quandrantal rules is UK outside controlled airspace when flying IFR and does not apply within standard airways.

[Jan Olieslagers]

Hope you're not really going to fly negative flight levels? Very few planes are certified there.

Seriously though: 't would be helpful if we knew what FIR you are writing about. Quadrantal rule is just one more UK oddity, but most people round here ARE from the UK.

[WhySoTough]

Thanks for the response all.

RichardH,

Firstly, up until FL 290 normally, and ABOVE FL290 at RVSM, just to clarify odds and evens.
Westbound : FL300, FL320, FL340, FL360, FL380, FL 400
Eastbound: FL310, FL330, FL 350, FL 370, FL 390
This correct?

I honestly did not understand what happens above FL 290 when NOT in RVSM conditions.
Also, what are the conditions and instruments needed in order to be under RVSM conditions?

I'm from the middle east btw, not UK.

[SinkRateSam]

Hi there!

That's correct. When RVSM is in effect between FL290 and FL410 (which is the case in pretty much all of Europe anyway) you would use the levels that you listed.

When outside RVSM, say above FL410, you will always need to use ODD levels to ensure a minimum separation of 2000ft between aircraft. This means that, WESTBOUND flights above FL400 (last usable even FL inside RVSM airspace) have to fly at FL430, FL470, FL510 etc. EASTBOUND flights flying above FL410 would fly at FL450, FL490, FL530 etc.

If you, however, fly in a country where RVSM has not been adopted above FL290, a westbound flight cruising above FL280 would have to choose FL310, FL350, FL390 etc. Accordingly eastbound flights cruising above FL290 would fly at FL330, FL370, FL410 etc.

Also your aircraft is permitted to fly inside RVSM airspace if it's equipment fulfills the following requirements:

Two independent altitude measurement systems At least one automatic altitude control system (tolerance band of ±65ft about and acquired altitude straight & level in nonturbulent, nongust conditions) An altitude alerting system (alerts ±300ft deviations) An altitude reporting SSR transponder Further limitations to the above can be found in ICAO docs.




Cheers
Hope this helped.