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the obstacle marking requirements of Chapter 6 should
continue to be met in relation to the displaced threshold.
10.2 Displaced threshold
11. Approach lighting systems
10.2.1 If an object extends above the approach surface
and the object cannot be removed, consideration should be
given to displacing the threshold permanently.
10.2.2 To meet the obstacle limitation objectives of
Chapter 4, the threshold should ideally be displaced down the
runway for the distance necessary to provide that the approach
surface is cleared of obstacles.
10.2.3 However, displacement of the threshold from the
runway extremity will inevitably cause reduction of the
landing distance available, and this may be of greater operational
significance than penetration of the approach surface
by marked and lighted obstacles. A decision to displace the
threshold, and the extent of such displacement, should therefore
have regard to an optimum balance between the considerations
of clear approach surfaces and adequate landing
distance. In deciding this question, account will need to be
taken of the types of aeroplanes which the runway is intended
to serve, the limiting visibility and cloud base conditions under
which the runway will be used, the position of the obstacles in
1 1.1 Types and characteristics
11.1.1 The specifications in this volume provide for the
basic characteristics for simple and precision approach lighting
systems. For certain aspects of these systems, some latitude is
permitted, for example, in the spacing between centre line
lights and crossbars. The approach lighting pattems that have
been generally adopted are shown in Figures A-5 and A-6. A
diagram of the inner 300 m of the precision approach category
I1 and I11 lighting system is shown in Figure 5-13.
11.1.2 The approach lighting configuration is to be
provided irrespective of the location of the threshold, i.e.
whether the threshold is at the extremity of the runway or
displaced from the runway extremity. In both cases, the
approach lighting system should extend up to the threshold.
However, in the case of a displaced threshold, inset lights are
used from the runway extremity up to the threshold to obtain
the specified configuration. These inset lights are designed to
ATT A-9 25/1Y04
Annex I4 - Aerodromes Volume Z
satisfy the structural requirements specified in Chapter 5,
5.3.1.9, and the photometric requirements specified in
Appendix 2, Figure A2-1 or A2-2.
1 1.1.3 Flight path envelopes to be used in designing the
lighting are shown in Figure A-4.
11.2 Installation tolerances
Horizontal
11.2.1 The dimensional tolerances are shown in
Figure A-6.
11.2.2 The centre line of an approach lighting system
should be as coincident as possible with the extended centre
line of the runway with a maximum tolerance o f f 15'.
11.2.3 The longitudinal spacing of the centre line lights
should be such that one light (or group of lights) is located in
the centre of each crossbar, and the interVening centre line
lights are spaced as evenly as practicable between two crossbars
or a crossbar and a threshold.
11.2.4 The crossbars and barrettes should be at right
angles to the centre line of the approach lighting system with
a tolerance of + 30', if the pattern in Figure A-6 (A) is adopted
or f 2", if Figure Ad (B) is adopted.
11.2.5 When a crossbar has to be displaced from its
standard position, any adjacent crossbar should, where possible,
be displaced by appropriate amounts in order to reduce
the differences in the crossbar spacing.
11.2.6 When a crossbar in ' the system shown in
Figure A-6 (A) is displaced from its standard position, its
overall length should be adjusted so that it remains onetwentieth
of the actual distance of the crossbar from the point
of origin. It is not necessary, however, to adjust the standard
2.7 m spacing between the crossbar lights, but the crossbars
should be kept symmetrical about the centre line of the
approach lighting.
1 1.2.7 The ideal arrangement is to mount all the approach
lights in the horizontal plane passing through the threshold
(see Figure A-7), and this should be the general aim as far as
local conditions permit. However, buildings, trees, etc., should
not obscure the lights from the view of a pilot who is assumed
to be lo below the electronic glide path in the vicinity of the
outer marker.
11.2.8 Within a stopway or clearway, and within 150 m
of the end of a runway, the lights should be mounted as near
to the ground as local conditions permit in order to minimize
risk of damage to aeroplanes in the event of an overrun or
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