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ICAO Preliminary Unedited Version — October 2008 II-1-3
An example of the working environment of air traffic controllers is shown in Figure 2. It should be
noted that good manual dexterity and neuromuscular co-ordination are required of controllers in the
discharge of their duties. Good visual acuity, both at distance and for reading is required, and the amount
of colour coded information makes good colour perception necessary. Furthermore, air traffic controllers
should be capable of spreading their attention over a number of tasks simultaneously.
Figure 2.— Air Traffic Controllers at their work stations
PHYSICS OF THE ATMOSPHERE
Barometric pressure
The earth is surrounded by a thin layer of gases and vapours in which two forces counteract: the kinetic
energy of the gas molecules leading them away from each other, and the gravitational attraction due to the
mass of the earth. This attraction is inversely proportional to the square of the distance. The action of
these two forces results in a decrease, with increasing altitude, in the density of the atmosphere and
therefore a decrease in the resulting barometric pressure which follows an exponential curve with
increasing altitude. Associated with this pressure event are other phenomena such as a temperature drop
and an increase in the intensity of solar radiation. From a biological viewpoint, the barometric pressure
drop is the most specific feature of the altitude climate. The manifestations directly related to reduced
barometric pressure per se are of two types:
a) mechanical (expansion of trapped gases); and
ICAO Preliminary Unedited Version — October 2008 II-1-4
0.2094 2
= × O B P P
( 47) 0.2094 2
= − × O B P P
b) biological (drop in oxygen partial pressure).
The chemical composition of the atmosphere remains constant up to an altitude of about 25 km
(82 000 ft). The oxygen fraction is about 20.94 per cent and the partial pressure (pO2) changes in direct
proportion to the total barometric pressure (PB) and can be calculated for dry gas as follows:
(1)
On entering the airways, the inspired gas becomes immediately saturated with water vapour at body
temperature. The partial pressure exerted by the water vapour at 37°C (98.6°F) is always 47 mm Hg
regardless of the total barometric pressure. This fact poses a special problem in aviation medicine because
it is obvious that with increasing altitude, the water vapour pressure represents an increasing proportion of
the inhaled gaseous constituents of the atmosphere. When considering the water vapour pressure, formula
(1) has to be modified as follows:
(2)
Since aviation operations are carried out in an environment different from the regular habitat of
humans, the designated medical examiner should be familiar with the physical characteristics of the
environment in which the flight crew operates.
ICAO Preliminary Unedited Version — October 2008 II-1-5
Table 1 shows the relationship between altitude, pressure and temperature as shown in a standard
atmosphere.
ALTITUDE PRESSURE TEMPERATURE
metres feet mm HG psia °C °F
sea level 760 14.7 15.0 59.0
400 1 312 725 14.0 12.4 54.4
600 1 968 707 13.7 11.1 52.0
800 2 625 691 13.4 9.8 49.6
1 000 3 281 674 13.0 8.5 47.3
1 500 4 921 634 12.3 5.3 41.5
2 000 6 562 596 11.5 2.0 35.5
2 500 8 202 560 10.8 −1.2 29.7
3 000 9 842 526 10.2 −4.5 23.9
3 500 11 483 493 9.5 −7.7 18.1
4 000 13 123 462 8.9 −11.0 12.2
4 500 14 764 433 8.4 −14.2 6.4
5 000 16 404 405 7.8 −17.5 0.5
5 500 18 044 379 7.3 −20.7 −5.3
6 000 19 685 354 6.8 −24.0 −11.2
6 500 21 325 331 6.4 −27.2 −16.9
7 000 22 966 308 6.0 −30.5 −22.9
7 500 24 606 287 5.6 −33.7 −28.6
8 000 26 246 267 5.2 −36.9 −34.5
10 000 32 808 199 3.8 −49.9 −57.8
12 000 39 370 146 2.8 −56.5 −69.7
14 000 45 931 106 2.0 −56.5 −69.7
16 000 52 493 78 1.5 −56.5 −69.7
18 000 59 054 57 1.1 −56.5 −69.7
20 000 65 616 41 0.80 −56.5 −69.7
25 000 82 020 19 0.37 −51.6 −60.9
30 000 98 424 9 0.17 −46.6 −51.9
Table 1.— The relationship between altitude (in ft),
pressure (in mm Hg and pounds per square inch (absolute)), and temperature (in °C and °F)
The range of environmental conditions encountered in civil aviation operations varies widely, from
those characteristic of unpressurized small aircraft and gliders, to those of subsonic and supersonic jets.
The relationship between barometric pressure and the operational ceiling of aircraft is shown in
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