Cruise Flight Levels

[GSLOC]

Good day,

We all know of general quadrantal rule of cruise flight levels (i.e. 180-359 even, 000-179 odd) applicable in most European states. However AIP section 3.2 (ATS routes) may prescribe direction of flight levels (odd or even) which is opposite to the mentioned rule. I.e portion of airway with magnetic track of say 270 is prescribed to be flown on odd flight level. It is clear that we should conform to section 3.2 of AIP when choosing FL's for flight planning purposes, but actually no document (even ICAO docs) say that there may be exception to general "table of cruise flight levels" and that you must refer to AIP for specific FLs on particular airways.

Could anyone point me at a specific doc which says that we must conform to AIP section 3.2 (ATS routes) for FL selection, rather then general table of cruise flight levels.

Thank you.

[GSLOC]

How comes that noone knows! Any dispatchers here?

[rudderrudderrat]

Hi ,

There is generally a note alongside the airway, on the Airway Charts that you use for planning your route.

[GSLOC]

How comes that no doc mentions that we must refer to AIP (section ATS routes) for actual FL selection, rather then "table of cruise flight levels"?

[rudderrudderrat]

Isn't that a bit like asking why we have to look at the one way roads atlas to find the distance across London?

[GSLOC]

My argument is as follows. Take any ICAO document, say 8168, 4444, or Annex 2 - according to them flight levels must be chosen according to the "table of cruise flight levels". Nowhere it is mentioned that there are exceptions and that exceptions are given in AIP. Actually even in AIP section Altimeter Setting Procedures there is typically also no mention of section 3.2 (ATS routes) - where those airways are given. It seems that AIP section of ATS routes is not interlinked with any other document and there is no referral to it. It seems to be completely isolated and hence you can not determine operational significance of its contents.

Do dispatchers rely on general "table of cruise flight levels" or refer to ATS routes section of AIP? What is significance of data given in ATS routes section regarding flight levels?

[Grasscarp]

Most flight dispatchers will be using computerised flight planning. These allocate a flight level according to what is loaded in the database in conjunction with winds and aircraft performance. The database is loaded with minimum and maximum flight levels according to the AIP and the rules for which levels are chosen are predicated by whether it is an RVSM area or not. There are also some airways which have different rules, but I am giving you a generalisation here of how it works.

[GSLOC]

Thank Grasscarp,

Surely it's all automated with taking into account winds, weight, etc, but when selecting direction of Flight Levels on particular airway - odd or even, do you rely on table of cruise flight levels or refer to ATS routes section of AIP?

Simple example. Airway X, from navaid A to C. Magnetic track 140. RVSM. According to "table of cruise flight levels", FL should be odd. However AIP prescribes even FL's on airway X from navaid A to C. Would you file for odd or even FL and why?

[Grasscarp]

The calculation looks at the available flight levels to match the upper and lower limits of the airway, separation rules and tracks. If they are non standard levels on a particular airway then the available levels will be loaded as per the AIP into the database. There is no other way to do it. You have to make the AIP the master document.

[enicalyth]

ICAO documents have no force in law. They are recommendations based on an idealistic model of the world and ICAO would be the first to admit that local adjustments are made by the lawful authorities where it is better to do so. As noted above you must follow the aip and the majority of countries do nowadays post the integrated aip as a download on the web The UK, France, Spain and Portugal are shining examples. Some countries, eg Austria, ask a fee.

Some countries such as Italy and the UK are notably "long and thin"; some countries such as France are more "square" but have say a predominant traffic flow E-W. Some passages such as the EURSAM corridor have one direction going in an airfield-rich environment with more advanced navigation aids than you can shake a stick at and the other... er, not. Some passages have the jetstream, some have the ITCZ. Thus there are many occasions where geography and meteorolgy are in conflict with the ICAO world model and commonsense must prevail.

A good example for you to follow once you have all the necessary iaips downloaded for the UK, France, Spain, Portugal and ASECNA is to plan a flight from Aberdeen through Faro, Casablanca, BULIS to Conakry. You will basically be on UP600 and UM322 for most of the way. If you can, dial up Jeppesen weather text. At the portion where UP600 becomes bilateral from unilateral and then becomes UR72 at the FIR/UIR boundary south of Faro to become RVSM of the opposite hand at BULIS it should begin to make sense. Air Law and Navigation orders are mandatory, you must follow the AIP or you'll find yourself in close formation with the military metal.

There are still some real lulus, notably where UG853 not only crosses the equator but also changes hemispherical direction. "You'all be care, yah hear now?" is the rule then and if you don't like what you see coming towards you, just shut your eyes, go right hand down a bit, count to ten and then resume navigation.

Best regards

the "E"