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Fig- A-7. Vmisal installdon toleranas
2511 1/04 A T I A-14
A#achment A Annex 14 - Aerodromes
11.3.3 It is recognized that some components of
electronic landing aids systems, such as reflectors, antennas,
monitors, etc., must be installed above the light plane. Every
effort should be made to relocate such components outside the
boundaries of the light plane. In the case of reflectors and
monitors, this can be done in many instances.
1 1.3.4 Where an ILS localizer is installed within the light
plane boundaries, it is recognized that the localizer, or screen
if used, must extend above the light plane. In such cases the
height of these structures should be held to a minimum and
they should be located as far from the threshold as possible. In
general the rule regarding permissible heights is 15 cm for
each 30 m the structure is located from the threshold. As an
example, if the localizer is located 300 m from the threshold,
the screen will be permitted to extend above the plane of the
approach lighting system by 10 x 15 = 150 cm maximum, but
preferably should be kept as low as possible consistent with
proper operation of the ILS.
11.3.5 In locating an MLS azimuth antenna the guidance
contained in Annex 10, Volume I, Attachment G should be
followed. This material, which also provides guidance on collocating
an MLS azimuth antenna with an ILS localizer
antenna, suggests that the MLS azimuth antenna may be sited
within the light plane boundaries where it is not possible or
practical to locate it beyond the outer end of the approach
lighting for the opposite direction of approach. If the MLS azimuth
antenna is located on the extended centre line of the runway,
it should be as far as possible from the closest light
position to the MLS azimuth antenna in the direction of the
runway end. Furthermore, the MLS azimuth antenna phase
centre should be at least 0.3 m above the light centre of the
light position closest to the MLS azimuth antenna in the
direction of the runway end. (This could be relaxed to 0.1 5 m
if the site is otherwise free of significant multipath problems.)
Compliance with this requirement, which is intended to ensure
that the MLS signal quality is not affected by the approach
lighting system, could result in the partial obstruction of the
lighting system by the MLS azimuth antenna. To ensure that
the resulting obstruction does not degrade visual guidance
beyond an acceptable level, the MLS azimuth antenna should
not be located closer to the runway end than 300 m and the
preferred location is 25 m beyond the 300 m crossbar (this
would place the antenna 5 m behind the light position 330 m
from the runway end). Where an MLS azimuth antenna is so
located, a central part of the 300 m crossbar of the approach
lighting system would alone be partially obstructed. Nevertheless,
it is important to ensure that the unobstructed lights of the
crossbar remain serviceable all the time.
may be located so close to the threshold that they cannot be
cleared by the 2 per cent slope. Where such conditions exist
and no alternative is possible, the 2 per cent slope may be
exceeded or a "stair step" resorted to in order to keep the
approach lights above the objects. Such "step" or increased
gradients should be resorted to only when it is impracticable to
follow standard slope criteria, and they should be held to the
absolute minimum. Under this criterion no negative slope is
permitted in the outermost portion of the system.
1 1.4 Consideration of the effects
of reduced lengths
1 1.4.1 The need for an adequate approach lighting system
to support precision approaches where the pilot is required to
acquire visual references prior to landing, cannot be stressed
too strongly. The safety and regularity of such operations is
dependent on this visual acquisition. The height above runway
threshold at which the pilot decides there are sufficient visual
cues to continue the precision approach and land will vary,
depending on the type of approach being conducted and other
factors such as meteorological conditions, ground and airborne
equipment, etc. The required length of approach lighting system
which will support all the variations of such approaches is
900 m, and this shall always be provided whenever possible.
11.4.2 However, there are some runway locations where
it is impossible to provide the 900 m length of approach
lighting system to support precision approaches.
11.4.3 In such cases, every effort should be made to
provide as much approach lighting system as possible. The
appropriate authority may impose restrictions on operations to
　
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