The purpose of taxiway lighting is to help ensure that both flight crew and vehicle drivers follow the correct taxiway routings at night and in low visibility and correctly stop as their ATC clearance limits. Lighting embedded in the useable surface of a taxiway or marking the edge of available movement areas can be expected to follow the international standards specified in ICAO SARPs unless information to the contrary is published for a particular airport in a State AIP.
Taxiway lighting is designated as either high intensity or low intensity. Lighting provided in support of low visibility operations can normally have the degree of luminance remotely selected to suit environmental conditions. The intensity options are usually set up by the ANSP, which will have operational control of the lighting system; the settings can be varied upon request by the user. The performance specification for high intensity lighting is defined by the need to provide guidance by day in low visibility conditions; the highest intensity settings are normally used in these conditions. Lower intensities are suitable for night operations. Low intensity lighting is provided where operations are carried out at night but not in low visibility conditions and the luminance intensity is normally not adjustable.
Centreline and Edge Lighting
Airports operating in low visibility have green centreline lighting on principal taxiways and blue edge lighting on minor taxiways. Where green centreline lighting is provided, blue taxiway edge lighting may also be provided as additional guidance on sections of taxiway that are assessed as potentially difficult to negotiate. It should be noted that green taxiway centreline lighting may also be installed on a runway just prior to a designated exit taxiway in order to give lead-off guidance. Lead-on guidance from designated runway holding points onto runway centerlines may also be provided but if it is, it will be illuminated only if a specific clearance to enter that runway from that position is current. The edge of aprons, turning and holding areas are usually marked by blue lights.
Airports which operate at night but not in low visibility will have either green centerline or blue edge lighting or a combination of the two at the discretion of the Airport Operator. Unless lighting is selectable (see below) then where any part of a taxiway equipped with centreline lighting is within a designated ILS-sensitive area (or is so close to a runway as to constitute an obstruction for aircraft landing or taking off from that runway) then that part of the centerline lighting will be marked with alternating green and yellow lights and aircraft and vehicles should not stop in such areas without obtaining explicit ATC approval.
Lighted Stop Bars
These are provided at LVP airports and consist of a row of lights spaced evenly across the taxiway normally at right angles to the centreline and showing red towards an approaching aircraft when lit. Where installed, they are positioned before all taxiway/runway intersections (see Runway Status Lights (RWSL)) and may also be provided at other appropriate points within the taxiway system. At some airports where a Stop Bar is located on or close to a bend in a taxiway, additional elevated red lights may be positioned just beyond each edge of the taxiway so as to improve awareness of the Stop Bar location.
Selectable Taxiway Guidance System
At airports where Category II and III operations take place or where ground movement requirements are complex, a Surface Movement Guidance and Control System (SMGCS) may be installed in order to simplify the ATC GND task. Such a system has selective switching of taxiway centreline lighting so that individually defined blocks of taxiway, each beginning and ending at a lit Stop Bar, can be individually illuminated ahead by ATC when a valid clearance has been issued. The associated stop bars are extinguished as an aircraft with a valid clearance approaches the next section of taxiway and the centreline lighting for that block is selected.
Taxiway Intersection Lights
These may be provided at some airports where there are multiple intersecting taxiways but no Taxiway Guidance System. They consist of a row of at least 3 steady yellow lights disposed symmetrically about the taxiway centerline and indicate that aircraft should give way to crossing traffic unless a specific clearance otherwise had been given by ATC.
Reflective Taxiway Edge Markers and Centreline Studs
These may be substituted for lights on taxiways that are only infrequently used and have the same colours as the equivalent lights would have.