Semicircular rules[PDF]

Introduction

The semi-circular rule is the basic rule for flight level or altitude selection in function of the aircraft heading in order to ensure basic vertical separation.

This semi-circular defines the available flight levels in the conventional airspace and also in the reduced vertical separation airspace (RVSM) when applicable between FL290 and FL410.

RVSM definition = reduced vertical separation minimum

Definition of odd and even flight levels

For answering to the need of flight level separation between the same types of flight, flight levels have been separated in two categories: the even and the odd flight level:
  • Even flight level: the last number before the final number 0 shall be even: FL 40, FL 60, FL 120…
  • Odd flight level: the last number before the final number 0 shall be odd: FL 50, FL 70, FL 130

Default worldwide semi-circular rule


For IFR flights

The default worldwide semi-circular rule is the East/West orientation of the flight level parity:
  • Your aircraft has track between 0° and 179°, your flight level or altitude must be odd.
  • Your aircraft has track between 180° and 359°, your flight level or altitude must be even

Semicircular ifr.png

By following the semi-circular rule, an IFR aircraft will limit possible conflicts between other aircraft coming in opposite direction by providing 1000ft separation between opposite west/east tracks.

For VFR flights

The VFR rules of flight level and/or altitude selection is the same as IFR ones with adding 500ft to all levels.
The default worldwide semi-circular rule is the East/West orientation of the flight level parity:
  • Your aircraft has track between 0° and 179°, your flight level or altitude must be odd.
  • Your aircraft has track between 180° and 359°, your flight level or altitude must be even

Semicircular vfr.png

By following the semi-circular rule, a VFR aircraft will limit possible conflicts between other aircraft coming in opposite direction by providing 1000ft separation between opposite west/east tracks.

Specific semi-circular rule


North/South rule

In some countries due to the IFR route or special regulations set by the local administration, the semicircular rule can be the North/South orientation of the flight level parity:
  • Your aircraft has track between 90° and 269°, your flight level or altitude must be odd
  • Your aircraft has track between 270° and 359° & between 0° and 89°, your flight level or altitude must be even.

Mix of rules

In some countries, (for example France), the default semi-circular rule is the east/west orientation, but national regulations publish fixed orientation of the airways that cancel the semi-circular rule where the route orientation is published. The orientation can deviate from the default definition.

Example: In France, 95% of the airway parities are oriented North/South whereas the basic semi-circular rule is East/West.

List of available flight levels and altitude (in feet)


In airspace below FL290 (in feet)

Semicircular table 1.png

In RVSM airspace between FL290 and FL410 (in feet)

Reduced Vertical Separation Minima (RVSM) reduces the vertical separation above FL 290 and below FL410 to 1,000 ft.

This allows aircraft to safely fly more optimum routes, gain fuel savings and increase airspace capacity by adding new flight levels.

In areas where feet are used for altitude and where, in accordance with regional air navigation agreements, a vertical separation minimum of 1000 feet is applied between FL290 and FL410 inclusive.

Semicircular table 2.png

In non-RVSM airspace between FL290 and FL410 (in feet)

If your airspace is non-RVSM airspace, a vertical separation minimum of 2000 feet is applied between FL290 and FL410 inclusive.

Semicircular table 3.png

Airspace above FL410 (in feet)

Semicircular table 4.png

List of available flight levels and altitude (in meters)


In metric airspace below S890 (in feet)

Semicircular table 5.png

In-RVSM metric airspace

In areas where metres (meter) are used for altitude and where, in accordance with regional air navigation agreements, a vertical separation minimum of 300 m is applied between 8 900 m and 12 500 m inclusive

Semicircular table 6.png

In a non-RVSM metric airspace

Semicircular table 7.png

Airspace above S1490 (in meter)

Semicircular table 8.png


See also

Reference

  • ICAO documentation Annex 2 - Rules of the Air - 10th Edition July 2005

Author

  • VID 150259 - Creation
  • VID 150259 - Wiki integration

DATE OF SUBMISSION

  • 18:27, 12 February 2020

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.