Find the direction, pick a level, check altimeter and cross-check, cross-check...

OBJECTIVES:

• Explain how the semi-circular level system works
• Know from what level the 2000 ft vertical separation minima applies in RVSM and Non-RVSM airspaces
• Explain the North-South semi-circular level system
• How to handle traffic from RVSM to Non-RVSM airspace and vice versa  

Introduction

To improve separation during cruising flight, pilots have to select a Level (Level means an Altitude or a Flight Level) according the direction of their flight. This is called the semi-circular cruising level system.

Pilots who fly more or less in the same direction select the same levels so aircraft from the opposite direction are passed above or below. This way, the risk of head-on collisions is reduced because there is slightly more time to see opposite traffic.

At 3000 ft AGL (Above Ground Level) or below: fly at any level or height in any direction, unless flying in controlled airspace or local regulations require otherwise.

Above 3000 ft AGL: select a Level according your flight rules (IFR or VFR) and your direction of flight. Find out if you will fly in RVSM or Non-RVSM airspace!

Check what rules apply in the country you want to fly by reading the regulations on it's Division webpage!

1. Standard East - West SEMI-CIRCULAR CRUISING LEVEL SYSTEM:

In order to improve separation, it was decided to allocate Levels (Flight levels or Altitudes) to aircraft according their Magnetic Cruising Track.

This is how it works:

1. determine the Magnetic Track (direction) of your flight
2. select either the RVSM or non-RVSM table depending the area of flight
3. pick an Altitude or a Flight Level according to the Magnetic Track
4. IFR Flight Levels (FL) always end with "0" (FL40, FL 50, FL 60, etc...).

   VFR Flight Levels (FL) end with "5" (FL45, FL 55, FL 65, etc...).

5. fill in the level you want to use in your Flight Plan

Flight level separation

Pressure altimeter instruments that were produced until the end of the previous century, were inaccurate above FL 290. The higher you flew, the bigger the error margin became.

With the introduction of Flight levels, the vertical separation between IFR levels was set at 1000 feet up to FL 290 (29.000 feet) and 2000 ft above that level.

Since the precision of the instruments had improved and because more flight levels were needed due to the increasing amount of traffic, RVSM (Reduced Vertical Separation Minima) areas have been introduced. RVSM provides six additional cruising levels between FL 290 and FL 410, resulting in substantial reductions in fuel costs and in-flight delays.

Check your charts when preparing your flight! There are exceptions.

Not all countries apply RVSM until now as you can see on the Chart below (Courtesy of FAA).

The European RVSM Airspace since October 2007 (Courtesy of Eurocontrol):

1.1 RVSM and MNPS

In the RVSM (Reduced Vertical Separation Minima) areas, a vertical separation of 1000 feet is maintained up to FL410. Above FL 410, only ODD flight levels are used to ensure the vertical distance between aircraft will always be 2000 ft.

Only aircraft that comply with the MNPS (Minimum Navigation Performance Specifications) are allowed in RVSM airspace. If not compliant, the aircraft has to stay below FL 290 if it's destination is below the RVSM area or if it is unable to cruise above FL 410.

For MNPS requirements and to be able to file the proper requested Flight Levels the flightplan, check "Guidelines for Pilots".

Similarly, ATC controlling in an area that includes RVSM airspace have to make sure to tick the RVSM box in IvAc . Check "Guidelines for ATC".

Flight level allocation

Flight Levels are used at and above the transition level only. Check the transition level that is used for each airport with your Division.

The standard rule is: up to FL 410, "Eastbound" traffic follow the odd flight levels and "Westbound" traffic follow the even flight levels.

Up to and including FL 410: the required minimum vertical spacing between aircraft is 1000 ft, so Flight Levels are defined in steps of 10:

Eastbound magnetic tracks (000º - 179º) at ODD flight levels: e.g. 70, 90, 110, 130, 150, ......250, 270, 290, 310, .... 370, 390, 410

Westbound magnetic tracks (180º - 359º) at EVEN flight levels: e.g. 80, 100, 120, 140, ......240, 260, 280, 300, ... 360, 380, 400

Above FL 410: required vertical spacing is 2000 ft and Flight Levels increase in steps of 20. This means that FL 420 is not available but FL 450 is used instead by aircraft flying in a south-westerly direction. The next flight level for traffic to the north-east is FL 470 and FL 490 instead of flight level 480 to a south-westerly direction etc...

Eastbound magnetic tracks (000º - 179º) at flight levels 450, 490, 530, 570, ....

Westbound magnetic tracks (180º - 359º) at flight levels 430, 470, 510, 550, ...

• Table of cruising levels in RVSM aispace for IFR flights (and VFR flights in controlled airspace)

• Table of cruising levels in RVSM airspace for VFR flights outside controlled airspace

Note: VFR flights shall not be flown above FL 200 unless authorized by Division Regulations.

1.2 Non-RVSM airspace

In the non-RVSM areas, a vertical separation of 1000 feet is maintained up to FL 290 only. Above FL 290, only ODD flight levels are used to ensure the vertical distance between aircraft will always be 2000 ft.

Flight level allocation

Up to and including FL290: the required minimum vertical spacing between aircraft is 1000 ft, so Flight Levels are defined in steps of 10:

Eastbound magnetic tracks (000º - 179º) at ODD flight levels: e.g. 70, 90, 110, 130, 150, ......250, 270, 290

Westbound magnetic tracks (180º - 359º) at EVEN flight levels: e.g. 80, 100, 120, 140, ......240, 260, 280

Above FL290: the required vertical spacing is 2000 ft and FL increase in steps of 20. This means that FL 300 is not available but FL 310 is used instead by aircraft flying in a south-westerly direction. The next flight level for traffic to the north-east is FL 330 and FL 350 instead of flight level 340 to a south-westerly direction etc...

Eastbound magnetic tracks (000º - 179º) at flight levels 290, 330, 370, 410, 450

Westbound magnetic tracks (180º - 359º) at flight levels 310, 350, 390, 430

• Table of cruising levels in Non-RVSM airspace for IFR flights (and VFR flights in controlled airspace)

• Table of cruising levels in Non-RVSM airspace for VFR flights outside controlled airspace

Note: VFR flights shall not be flown above FL 200 unless authorized by Division Regulations.

2. North - South SEMI-CIRCULAR CRUISING LEVEL SYSTEM:

RVSM airspace

Some countries may have another cruising level system to manage their main traffic flows.

In general, when nothing is indicated, the standard semi-circular system (East-West) has to be used. According to the country you are flying in, you may be instructed to use levels different from those normally used in the standard semi-circular rule.

In France, Spain, Portugal and Italy for instance, ODD levels are used for magnetic tracks from 090° to 269° and EVEN levels for magnetic tracks from 270° to 089°. This is usually shown on navigation maps (on French maps, a little arrow applied next to airways names shows the way for ODD levels). It is still called a semi-circular system, but North-South configuration.

As mentionned earlier, the RVSM (Reduced Vertical Separation Minima) areas, a vertical separation of 1000 feet is maintained up to FL410. Above FL 410, only ODD flight levels are used to ensure the vertical distance between aircraft will always be 2000 ft.

Only aircraft that are equipped with modern altimeters and comply with the MNPS (Minimum Navigation Performance Specifications) are allowed in RVSM airspace. If not compliant, the aircraft has to stay below FL 290 if it's destination is below the RVSM area or if it is unable to cruise above FL 410.

But within the world of flightsimming MNPS cannot be applied. Therefore within IVAO we consider that all aircraft capable of flying above FL 290 are MNPS approved and may use the RVSM area.

However, to be able to file the proper requested flight levels the flightplan, check "Guidelines for Pilots".

Similarly, ATC controlling in an area that includes RVSM airspace have to make sure to tick the RVSM box in IvAc . Check "Guidelines for ATC".

Flight level allocation

Flight Levels are used at and above the transition level only. Check the transition level that is used for each airport with your Division.

Up to FL 410, "Northbound" traffic follow the even flight levels and "Southbound" traffic follow the odd flight levels.

Up to and including FL 410: the required minimum vertical spacing between aircraft is 1000 ft, so Flight Levels are defined in steps of 10:

Northbound magnetic tracks (180º - 359º) at EVEN flight levels: e.g. 80, 100, 120, 140, ......240, 260, 280, 300, ... 360, 380, 400

Southbound magnetic tracks (000º - 179º) at ODD flight levels: e.g. 70, 90, 110, 130, 150, ......250, 270, 290, 310, .... 370, 390, 410

Above FL 410: required vertical spacing is 2000 ft and FL increase in steps of 20. This means that FL 420 is not available but FL 450 is used instead by aircraft flying in a south-westerly direction. The next flight level for traffic to the north-east is FL 470 and FL 490 instead of flight level 480 to a south-westerly direction etc...

Northbound magnetic tracks (180º - 359º) at flight levels 430, 470, 510, 550, ...

Southbound magnetic tracks (000º - 179º) at flight levels 450, 490, 530, 570, ....

• Table of cruising levels in North - South RVSM airspace for IFR flights (& VFR flights in controlled airspace)

• Table of cruising levels in North - South RVSM airspace for VFR flights outside controlled airspace

Note: VFR flights shall not be flown above FL 200 unless authorized by Division Regulations.

From East - West to North - South cruising level system

To show the important difference between the application of E-W and N-S, here an example:

In the E-W configuration, if my track is 220 degrees, the flight level options are e.g. FL 320, FL 340 or FL 360.

But in the N-S configuration, if my track is 220 degrees, the flight Level options are e.g. FL 330, FL 350 or FL 370.

Now the other way around.

In the E-W configuration, if my track is 060 degrees, the flight level options are e.g. FL330, FL350 or FL370.

This track 060 is exactly opposite to the track 220 here above. If you would not respect the N-S rule, we may meet somewhere in the mid-air because we'd use the same levels in the opposite direction!

Rule of thumb:

3. RVSM Transition airspace from and to non-RVSM area's

When you fly in RVSM airspace, flight levels 310, 350 and 390 are used in one direction and in non-RVSM airspace they are used in the opposite !

RVSM Transition airspace is the "buffer" area that serves to put aircraft on the proper Flight Levels before entering RVSM or non-RVSM airspace.

• Standard East - West configuration

Here is the scheme for the standard East-West semi-circular configuration, in RVSM and Non-RVSM airspace.

A very important fact! If you do not apply the system correctly, you may end up with (unexpected?) opposite traffic at the same level!

• The North-South configuration

There are a number of countries that have good reasons to apply a different semi-circular system. In Europe these countries are (mainly) France, Italy, Spain and Portugal.

These countries apply the semi-circular system in a North-South direction. That applies equally above and below FL290!! This means that southbound traffic uses the odd levels and northbound the even levels. Again, check your maps when planning your flight. There are exceptions!!

Note that in fact the E-W semi-circular system has been turned by 90 degrees to the right to become the N-S semi circular system.

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(Sources: Annex 2 - Rules of the Air / Doc 8168 - Aircraft Operations - Vol. 1 / Doc 4444 - Air Traffic Management / Doc 9574 Manual on the Implementation of a 1000 ft Vertical Separation Minimum between FL 290 and FL 410 included)

Module Manager e-mail: acm@ivao.aero and acam@ivao.aero

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