¶ INTRODUCTION
This article’s goal is to help the air traffic controller to use the correct altimetry in his airspace. You will learn the different terms and how to use them.
In their airspace, air traffic controllers must define the transition altitude and transition flight level. These data are available through airfield ATIS information or on charts.
¶ TRANSITION ALTITUDE
The transition altitude is the upper limit from the surface to use the local QNH altimeter setting, applicable to all aircraft defined inside the associated TMA (terminal area) where it is published.
The transition altitude is also :
- Published on charts (IAC, ARR, DEP)
- Broadcasted in the ATIS of the air traffic controller.
- Usually given in feet but can be in meters in some countries.
Transition Altitude abbreviation defined by ICAO is TA.
Example of typical transition altitudes:
- In Europe, dependent on the airfield (usually below 10000ft and above 4000ft).
- In USA, there is one unique transition altitude at 18000ft.
The transition altitude of an aerodrome should not be below 3000ft.
¶ TRANSITION LEVEL
The transition level is the lower limit to use the standard 1013hPa altimeter setting, applicable to all aircraft defined inside the associated TMA (terminal area) where transition altitude is published.
The transition level is also:
- Sometimes published on charts (IAC, ARR, DEP) but not often.
- Usually calculated by the air traffic controller in function of transition altitude and QNH.
- Broadcasted in the ATIS of the air traffic controller.
- Always given in flight level.
Transition Level abbreviation defined by ICAO is TRL.
Note that in some charts or documentation, you may find the use of TL abbreviation instead of TRL.
¶ TRANSITION LAYER
The transition layer is the airspace located between the transition altitude and the transition level. The transition layer is defined inside the associated TMA (terminal area) where the transition altitude is published.
The altitude of the transition level shall always be greater than or equal to the transition altitude.
No cruise flight in the transition layer is permitted. An aircraft can only cross the transition layer.
¶ TRANSITION LAYER THICKNESS
The transition layer thickness is laid down in country regulations and can be:
- Between 0ft and 999ft.
- Between 0ft and 499ft.
- Between 1000ft and 1999ft.
- Between 1000ft and 1499ft.
Consult your national regulation documentation or ask your training or ATC operation staff in order to have this value. Per default use the value "Between 1000ft and 1999ft".
¶ EXPRESSION OF VERTICAL POSITION OF AIRCRAFT
For flights in the vicinity of aerodromes and within terminal control areas the vertical position of aircraft shall be expressed in terms of:
- altitudes at or below the transition altitude
- flight levels at or above the transition level.
While passing through the transition layer, the vertical position shall be expressed in terms of flight levels when climbing and in terms of altitudes when descending.
For flights en route, the vertical position of aircraft shall be expressed in terms of:
- flight levels at or above the lowest usable flight level
- altitudes below the lowest usable flight level
¶ NO TRANSITION ALTITUDE PUBLISHED
The default transition altitude, outside TMA or airspaces with no altitude transition published, should be 3000ft above the surface (height). In this case there is no transition level.
- none
- ICAO DOC 4444 Air Traffic Management 16th Edition 2016 - Chapter 4.10
- VID 150259 - Creation & Wiki integration
- VID 150259 - Update September 2019
- VID 545587- Wiki Migration