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50N the maximum total body dosage at 65 000 ft (~20 000 m) – an altitude approximating the cruise
altitude of SST aircraft - is about 0.013 mSv/hour. Because of the reduced journey time the dosage per
unit of distance traveled is about the same as in current subsonic jets where 0.005 mSv/hour is recorded
during flights at about 37 000 ft (11 000 m) and at latitudes around 45ΕN. CR is not therefore expected to
be significantly more hazardous to the flight crews and passengers of SST aircraft, as even if the mileage
flown by crews were to be doubled, the effects of CR would not be regarded as harmful. As previously
stated, Annex 6, Part I, (paragraphs 6.12 and 11.1.17) contains provisions concerning radiation
monitoring in aeroplanes operated above 49 000 ft (15 000 m).
5A radiation warning device (an in-flight radiation dosimeter) was used in the Anglo-French supersonic transport
(SST) aircraft Concorde. This device provided a continuous display of the radiation dose rate.
ICAO Preliminary Unedited Version — October 2008 II-1-15
OZONE
Ozone is triatomic oxygen, O3. Stratospheric ozone is formed by the action of ultraviolet light on oxygen
(3 O2 > 2 O3). It is found in varying quantities, the peak values being recorded at about 35 000 m
(115 000 ft) with negligible values at or below 12 200 m (40 000 ft) and much reduced levels above
42 700 m (140 000 ft). The cruise altitude of commercial SST aircraft in northern latitudes, about 18 450
m (60 000 ft), could produce levels of ozone of 2 000-4 000 μg/m3 (1-2 parts per million (ppm)). Ozone is
destroyed by heat, by the catalytic action of some materials including nickel and by organic compounds.
Total destruction occurs at 400°C (750°F). Air in the cabin pressurization system of one type of SST
(when SST public transport operations were undertaken) is heated to 600°C (1 120°F) and this heat is
utilized to destroy ozone. However, it has been reported that when engine power is reduced to initiate
descent, this manoeuvre is accompanied by a fall in the temperature of the cabin pressurization system
which could permit a potential buildup of ozone. During descent, levels of 400-1 000 μg/m3 (0.2-0.5 ppm)
may be experienced for about ten minutes within the pressurized section of the aircraft. The existing data
on the health effects of ozone, considered in conjunction with its high natural background level, lead to
the recommendation of a 1-hour guideline in the range of 150-200 μg/m3 (0.076-0.1 ppm). To lessen the
potential for adverse acute and chronic effects and to provide an additional margin of protection, an 8-
hour guideline for exposure to ozone of 100-120 μg/m3 (0.05-0.06 ppm) is recommended by the World
Health Organization (WHO). Tests, based on the exposure concentrations and time intervals calculated
for SST aircraft, have been conducted by the Medical Research Council of the United Kingdom and
showed no significant functional impairment. Although the original research concerning ozone and
aviation was undertaken for SST operations, catalytic converters were recommended by the UK House of
Lords Select Committee on Science and Technology to be fitted to subsonic aircraft when they could be
expected to fly through higher concentrations of ozone. Such equipment is now standard on many modern
aircraft.
ACCELERATION EFFECTS
Short-term accelerations
Speed itself in straight and level flight has no effect on the human body; accelerations due to changing
speed and/or direction of flight may, on the other hand, produce very considerable physiological effects
upon the occupants of an aircraft depending on the following factors:
a) magnitude, rate and direction of acceleration;
b) duration;
c) area of application; and
d) protection.
Accelerations of relatively short duration, usually less than a second, are associated with situations
such as flying in turbulence or emergencies such as crash landings. The critical protective factor for
short-term accelerations and rapid decelerations is the availability of restraint systems. The desirability of
shoulder harnesses for flight crew has been documented, taking into account not only crash protection but
also the possibility of on-duty incapacitation of a kind that might interfere with the operation of flight
controls.
The reader is referred to other texts for information relating to long-duration accelerations and other
aspects relevant to in-flight acceleration. Acceleration effects may result in sensory illusions (see below).
ICAO Preliminary Unedited Version — October 2008 II-1-16
SENSORY ILLUSIONS
The sensory perceptors of the human body associated primarily with maintaining equilibrium and
orientation are the eyes, the inner ears and proprioceptors in muscles, tendons and joint capsules. Their
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Manual of Civil Aviation Medicine 1(64)
