Description

The essential principles of both surface markings and signs used at licensed civil airports, with surfaced taxiways and served by public transport flights, can be expected to be in accordance with ICAO Standards and Recommended Practices (SARPS) unless an entry to the contrary appears in the State AIPs AGA section.

Taxiway Designations

Standard taxiway designation is by use of single letters of the alphabet for each discrete taxiway as, for example 'A' for taxiway Alpha, 'B' for Bravo etc. The letters 'O', 'I' and 'X' are not used. At large airports where there are more taxiways than letters of the alphabet, double letter designators may be used for minor taxiways or taxiway stubs. Local exceptions, in the form of additions to the standard designation system, may be found as, for example, with the use of ‘Inner’ and ‘Outer’ and at large airports, principal taxiways may be split into zones or ‘blocks’ and numbered uniquely.

Taxiway Surface Markings

All painted makings on the pavement surface are coloured yellow. There are five types:

• Centreline marking consists of a single continuous line marking the centre of the taxiway. Where a taxiway crosses a runway, the Taxiway Centreline Marking indicates the route to be followed but the marking is interrupted as necessary so as not to interfere with the runway markings. Taxiway centrelines should be located so that there is safe clearance between the largest aircraft that is permitted to use the taxiway and fixed objects or protected zones that the extremities of an aircraft on the taxiway centreline could impact, such as buildings and aircraft stands. At any runway-taxiway intersections where the taxiway centreline is curved onto the nearside of the runway centreline, pilots should take into account any loss of Runway Declared Distances incurred in following this ‘lead-on’ line when lining up for take-off.
• Runway Taxi-Holding Position (RTHP) markings occur on each taxiway leading to a runway in order to prevent taxiing aircraft and vehicles penetrating the designated protection zone either side of a runway, which needs to be kept clear during runway use. This zone will also, where applicable, allow for the protection of the ILS Sensitive Area. There are two forms of RTHP marking:
  • Two solid and two broken lines across the full width of the taxiway normally at right angles to its centerline with the broken lines closest to the runway.
  • A “ladder” mark laid across the full width of the taxiway and normally at right angles to its centerline.

If only one type is present, it will always be the former. Where there is more than one RTHP, all the additional ones will be of the second type. All RTHP should be located so that there is safe clearance between any aircraft holding there and any aircraft passing in front of the holding aircraft, subject to it being correctly positioned with no part of the aircraft on or beyond the line. There is no guarantee of any clearance behind a holding aircraft.

• Intermediate Taxi-Holding Position (ITHP) markings may be found at airports where the taxiway layout is complex or involves many intersecting taxiways. ITHPs may be established in order to protect a priority taxiway route ahead of the marking and are marked by a single broken line laid across the full width of the taxiway normally at right angles to its centerline. All RTHP should be located so that there is safe clearance between any aircraft holding there and any aircraft passing in front of the holding aircraft, subject to it being correctly positioned with no part of the aircraft on or beyond the line. There is no guarantee of any clearance behind a holding aircraft.
• Edge markings are used where the area beyond the taxiway edge is paved but not designated for use by aircraft.
• Information markings in the form of directions are sometimes provided as an alternative to a sign or to help prevent runway incursions.

Taxiway Signs

Signs are classified as either ‘Mandatory’ or ‘Information’ and are designed to provide simple surface movement guidance and control especially when Low Visibility Procedures(LVP) are in force. Both types are lit either internally or externally for night and low visibility operations where an airport operates under LVP, and may be lit for night operations at airports which do not operate under LVP.

Mandatory Signs have white characters on a red background and require a specific ATC clearance to a point beyond them before they are passed. They are of three types:

• Runway Taxi-Holding Position (RTHP) signs are located adjacent to the corresponding surface marking and show the direction in which the holding instruction applies. Unless there is only one taxiway serving a runway and only one RTHP on a particular taxiway, a ‘Location’ sign (see below) should be attached or immediately adjacent to an RTHP sign so as to identify the position. If only Visual operations occur, there may only be a sign on one side, normally the left. If Visual and Category I operations take place, a sign displaying the designator of the runway ahead should be on both sides of the taxiway. Where a taxiway provides access to a runway other than near one end, both runway designators will be shown with corresponding arrows indicating the direction to the threshold. Where Category ll and lll Operations take place, RHTP signs will be present at each marked position.
• Intermediate Taxi-Holding Position (ITHP) signs are located adjacent to the corresponding surface marking and display the Taxiway designator and a number identifying the particular holding position;
• No Entry signs are used where access is restricted to traffic in one direction only or out of use altogether. They are located on both sides of the taxiway facing the direction from which entry is prohibited;

Information Signs have a combination of yellow and black markings and are provided at the discretion of the airport operator to provide additional guidance to taxiing aircraft. There are two types:

• Location signs are used to identify taxiways and, where necessary, runways at complex intersections. Runway Location Signs always use the first two numbers of the runway magnetic heading. A Location Sign consists of the characters identifying the runway or taxiway in yellow characters against a black background surrounded by a yellow border. Where there is a need to identify a specific position on a taxiway, a Location Sign showing the taxiway designator and a unique location number is provided. Where individual taxiways are divided into zones or ‘blocks’ and uniquely identified, this identification will be displayed on Information Signs at each change of zone/block;
• Direction and Destination signs are marked with a route or destination and an arrow pointing in the appropriate direction which is displayed in black characters on a yellow background. Direction Signs are usually co-positioned with a Location sign and appear only on the left hand side.

Further Reading

• ICAO Doc 9157 Aerodrome Design Manual Part 4 : Visual Aids (4th edition 2004)
• FAA Engineering Brief No. 89 Taxiway Nomenclature Convention (2012)
• Visual Aids Handbook UK CAA CAP 637 (2007)
• ICAO Runway Excursion Risk Reduction Toolkit - Aerodrome Best Practice (2nd edition)
• AC 150/5210-20A: Ground Vehicle Operations to include Taxiing or Towing an Aircraft on Airports, FAA, September 2015