In establishing a landing area, it is essential to ensure
a safe correlation between:
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.1 the dimensions of the aiming circle, clear
zone and manoeuvring zone and the maximum permitted height of obstructions
in these zones; and
-
.2 the sizes of helicopters expected to use the
facility.
In particular, the clear zone of the landing area should be
as large as practicable. Its diameter D should be not less than the
overall length of a helicopter (with its rotors turning) (d) which
may use it. Other dimensions of the landing area should be in proportion
to the diameter of the clear zone, as illustrated in figures 1 and 2.