Which flight Level?

[CTLHC]

This may seem a really stupid question, but why do we fly odd FLs down to the Canaries and evens back when the Aerad Book Rules of the Air page 11 clearly states that for RVSM airspace it should be odds from 000 to 179 and then evens from 180 to 359?

Strange how theses things are done contrary to the guidance.

[Background Noise]

Some airways have specific levels which go against standard. Usually when they alternate either side of the division eg east or west of south. Otherwise you would be changing levels at every corner.

[pakeha-boy]

not sure what the equivalent to the UK version is ;.....

But the TERPS....(I will try to copy and paste) has the defintion and reasons for this....

[CTLHC]

That's Ok and I understand that, but the track from UK to the Canaries doesn't ever become east of south and the return doesn't ever become west of North.

Still doesn't make sense.

[alexban]

same if flying fom italy to spain,for ex fco-mad. Over ALG you should change from even to odd levels.

[Penworth]

I believe its due to the regulations in certain countries, eg. France, where most of the traffic is North-South so for them is makes sense to operate contrary to the guidance and have northbound traffic flying at even levels and southbound traffic flying at odd levels.

At least, that's how it was explained to me during line training.

PW

[threemiles]

That's Ok and I understand that, but the track from UK to the Canaries doesn't ever become east of south and the return doesn't ever become west of North.

A number of European south-west/north-east routes have historically always been exempted from the semi-circular rule. They are (almost) straight these days but have not been always some 20 years ago, when there was much more flying around military areas in Portugal and Northern Spain. Routes aka UN866 etc. are still even northeastbound between Canarias TMA southern border and Denmark FIR boundary. In Germany most routes are exempted, too, because there was no real east-west traffic flow before 1990 (except in the Berlin corridors below FL100) and many routes go slightly north-east then north-west then north-east...

[ahramin]

Oakland Center in the U.S.A. has the same policy, even alts for North-East and odd alts South-West flights.

It's all about what works best for a particular geography of routes.

[78deg]

I believe the European Region has filled a difference with ICAO

[enicalyth]

Read the small print.

France, Iberia, West Med, North Africa, French-Speaking Africa do tend to favour the Evens North Odds South. So the UK, AENA, ASECNA and the EUR/SAM corridor I think file differences and have consistency at least from about Conakry Northwards.

It may be that at some point the levels were chosen to favour those going South agin the wind. For there are Northbound routes that swing hemispheres to allow Southbound travellers to hold the weather advantage and have the shorter route. Consistency of level and directions is therefore important.

Examples. VFA-ARE-ORTAC is a Northbound route all one hemisphere. But how about BAROK-SNT-SALCO? There is a very definite dogleg at SOTEX so AENA have you Northbound on Evens despite being in the other hemisphere until you reach SNT. The corresponding Southbound Odd into the wind is much more direct as SALCO-VES-ESP-BAROK. So there is some method in the madness. BAROK-SNT-SALCO swings and VFA-ARE-ORTAC does not but they are both Northbound and Even.

There are peasant traps. Just be careful at TITOR on UG853 where the sense changes at a prominent dogleg as you transit from ASECNA into Angola, Namibia and South Africa. So always worth a chat with "Haven". They do respond to civilian traffic, and monitor all their frequencies not just the predicted ones. Sometimes it gets awful quiet out there.

Early in my career I was told that Africa starts south of the River Po and finishes overhead Wolseley. Therefore if someone has established Evens Up Odds Down don’t for heavens sake change it. Mind you I suppose we could do it in stages. Light aircraft change over on Mondays, helicopters on Tuesdays, Medium on Wednesdays, Military on Thursdays, Heavy on Fridays…