2.1_ Altimetry

2.1.1_ Altitudes

Altitude is the vertical position of an aircraft in relation to the mean sea level and is expressed in feet AMSL. Altitude is determined using the altimeter corrected for pressure by using the local QNH or Altimeter setting. Altitudes are used below the Transition Altitude.

EXAMPLE: 7'000 Seven Thousand
EXAMPLE: 12'500 One Two Thousand Five Hundred


2.1.2_ Flight Levels

A Flight Level is the vertical position of on aircraft above the isobaric surface. The Flight Level is determined using Standard pressure (1013.25mb / 29.92"hg). Flight Level are used above the Transition Altitude, and are expressed in in hundreds of feet.

EXAMPLE: 9'000 Flight level niner zero (FL090)
EXAMPLE: 27'500 Flight level Two seven fife (FL275)


2.1.3_ Transition Altitude

Transition Altitude is the altitude at or below pilots use the local QNH/Altimeter setting and fly using altitudes. In North America the TA is always 18'000ft. In the rest of the world TA will vary, usually in the 4,000 - 7,000ft range.


2.1.4_ Where to find the TA/TL

Transition Altitude is published on the approach/departure charts of most aerodromes, and many controllers add it to the ATIS. In North America TA is fixed at 18'000ft


2.1.5_ Correct altitudes for direction of travel

In order to regulate traffic, and ease ATC workload, the semi-circular rule has been created, assigning specific altitudes to aircraft depending on their direction of travel.


CVSM airspace (Southern africa, Northern Asia)
Eastbound magnetic track (000°- 179°)
Odd Altitudes
Westbound magnetic track (180°-359°)
Even Altitudes
FL 50 or 5,000 ft
FL 70 or 7,000 ft
FL 90 or 9,000 ft
FL 110 or 11,000 ft
FL 130 or 13,000 ft
FL 150 or 15,000 ft
FL 170 or 17,000 ft
FL 190
FL 210
FL 230
FL 250
FL 270
FL 290
-------------
FL 330
FL 370
FL 410

...
FL 40 or 4,000 ft
FL 60 or 6,000 ft
FL 80 or 8,000 ft
FL 100 or 10,000 ft
FL 120 or 12,000 ft
FL 140 or 14,000 ft
FL 160 or 16,000 ft
FL 180
FL 200
FL 220
FL 240
FL 260
FL 280
-------------
FL 310
FL 350
FL 390

...


RVSM airspace (everywhere else)
Eastbound magnetic track (000°- 179°)
Odd Altitudes
Westbound magnetic track (180°-359°)
Even Altitudes
FL 50 or 5,000 ft
FL 70 or 7,000 ft
FL 90 or 9,000 ft
FL 110 or 11,000 ft
FL 130 or 13,000 ft
FL 150 or 15,000 ft
FL 170 or 17,000 ft
FL 190
...
FL 290
FL 310
FL 330
FL 350
FL 370
FL 390
FL 410
-------------
FL 450
FL 490
FL 530
...
FL 40 or 4,000 ft
FL 60 or 6,000 ft
FL 80 or 8,000 ft
FL 100 or 10,000 ft
FL 120 or 12,000 ft
FL 140 or 14,000 ft
FL 160 or 16,000 ft
FL 180
...
FL 280
FL 300
FL 320
FL 340
FL 360
FL 380
FL 400
-------------
FL 430
FL 470
FL 510
...

IMPORTANT: Some countries modify the directional division of even/odd altitudes. For instance in France, Italy, Spain, Protugal, and Switzerland the Odd/Even rule is divided along North/South headings so: North (270°-089°) is Even altitudes and South (090°-269°) is Odd alitiudes, and in New Zealand it's the iverse.

FAA RVSM Diagram
Diagram of RVSM and CVSM airspace.

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