Draft ICAO Circular on NLA.pdf - Airports Council International

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4.1.4.3.5 Special attention should be given to the offset of centre line lights in relation to centre line
markings. Especially during winter conditions, distinction between markings and offset lights could be
difficult.
4.1.4.4 Taxiway curves and intersections
4.1.4.4.1 Annex 14, Volume I, paragraph 3.8.5 recommends provision of suitable curves to ensure that
when the cockpit remains over the taxiway centre line, the outer main wheel edge maintains a 4.5 m
clearance from taxiway edge.
4.1.4.4.2 Aerodrome Design Manual, Part 2 contains related guidance in paragraphs 1.2.9 and 1.2.22
and Table 1-3.
4.1.4.5 Hazard identification and analysis
4.1.4.5.1 Any hazard will be the result of a lateral taxiway excursion on a curved section.
4.1.4.5.2 The causes of such an event could be classified as the same as for a taxiway excursion on
a straight taxiway section. The use of cockpit-over-centre line steering technique on curved taxiway will
result in track-in of the main landing gears from the centre line. The amount of track-in depends on the radius
of the curved taxiway and the cockpit-to-main landing gear distance.
4.1.4.5.3 Consequences are the same as for lateral taxiway excursions on straight sections.
4.1.4.6 Risk assessment and possible mitigation measures
4.1.4.6.1 The required width of curved portions of the taxiways is related to the clearance between
the outer main wheel and the taxiway edge on the inner curve. The hazard is related to the combination of
outer main gear wheel span and the distance between nose gear/cockpit and main gear. Consideration may
need to be given to the effect of jet blast from a turning aircraft on airfield signs and other objects nearby.
4.1.4.6.2 Though the outer main gear wheel span of certain aircraft place them in code E, the effect
of the longer wheelbase on taxiway junctions will require wider fillets.
4.1.4.6.3 Possible mitigation measures for operation of NLA on taxiway curves and sections not
conforming to Annex 14, Volume I specifications are:
a) widening existing fillets or providing new fillets;
b) reduced taxi speed; and
c) provision of taxiway centre line lights and taxi side stripe markings (and taxiway edge
lights).
4.1.4.6.4 Special attention should be given to the offset of centre line lights in relation to centre line
markings. Especially during winter conditions distinction between markings and offset lights could be
difficult.
<strong>ICAO</strong> Version 4.1 — 15 March 2004