TAXIWAY VISUAL GUIDANCE
Taxiway signs and markings are a major part of the Surface Movement Guidance and Control System (SMGCS). They help pilots and vehicle operators know their position, follow the route, recognise holding positions, avoid restricted areas and navigate intersections.
The key distinction
- Marking = information painted on the pavement
- Sign = information on an elevated or surface-mounted sign
- Lighting = makes the visual guidance available under the operating conditions
The references are AC 150/5340-18H (sign systems), AC 150/5340-1M (markings) and AC 150/5345-44L (sign specification). For the marking-vs-lighting principle see Note 12.
TAXIWAY MARKINGS
| Marking | Description |
|---|---|
| Centerline | Single continuous yellow line, 6–12 in (15–30 cm) wide |
| Enhanced centerline | Normal centerline plus parallel yellow dashed lines each side, up to 150 ft (45.7 m) before a runway holding position; warns of approaching a hold |
| Edge, continuous | Double continuous yellow, each line at least 6 in, 6 in apart; outside area not intended for aircraft |
| Edge, dashed | Broken double yellow, 6 in lines, 6 in spacing, 15 ft segments, 25 ft gaps; adjoining pavement (e.g. apron) can be used by aircraft |
| Shoulder | Yellow where needed to show pavement that looks usable but is not |
Taxiway centerline, edge, shoulder and holding positions are yellow, unlike the mostly white runway markings. Memory: solid = not a normal taxi area · dashed = crossing may be intended. Being on the centerline does not by itself guarantee wingtip clearance.
HOLDING POSITION MARKINGS
| Holding position | Marking | Sign |
|---|---|---|
| Runway | Pattern A: four yellow lines, two solid and two dashed; solid lines on the holding side | Red background, white legend with black outline (runway designations, e.g. 15-33) |
| ILS critical area / POFZ | Pattern B: two solid yellow lines 2 ft apart with connecting pairs of lines at 10 ft spacing | White legend on red: “ILS” |
| Taxiway / taxiway | Pattern C: single dashed yellow line across the taxiway (“hold short of Taxiway XX”); optional, used where aircraft are held short of an intersection | No mandatory sign; the location/direction array may sit up to 10 ft before the line |
| Approach / departure area | Pattern B, as for ILS | Red, white legend: runway designation + APCH and/or DEP (e.g. “15 APCH – 33 DEP”) |
The marking says where to stop; the sign says what you are holding for. The runway numerals on the sign show the relative direction of the thresholds: on a “15-33” sign, runway 15 is to the left and runway 33 to the right when facing the runway from the holding position. FAA signs write single-digit runways without a leading zero (9-27); ICAO and Indian practice uses two digits (09-27). Marking is not replaced by the sign: keep both maintained.
RUNWAY
══════════════════════
[ 27-9 ] sign: WHAT
─ ─ ─ ─ ─ ─ ─ ─ dashed (runway side)
═══════════════ solid (holding side)
TAXIWAY hold line: WHERESURFACE-PAINTED SIGNS AND GEOGRAPHIC MARKINGS
| Surface-painted sign | Colours | Position |
|---|---|---|
| Direction | Yellow background, black inscription | Adjacent to centerline: left-turn signs on left, right-turn signs on right |
| Location | Black background, yellow inscription | Right side of centerline |
| Holding position | Red background, white inscription | Left of the centerline on the holding side, before the holding-position marking; normally used where the holding-position width exceeds 200 ft (60 m) |
Surface-painted signs supplement elevated signs; they do not replace the standard elevated mandatory or direction signs. Geographic-position markings are placed to the left of the centerline, in the direction of taxiing, along low-visibility (RVR below 1,200 ft / 360 m) taxi routes designated in the SMGCS plan: a circular design in black, white and pink with a number or number/letter identifier.
TAXIWAY DESIGNATIONS
Designations should be simple and logical. AC 150/5340-18H introduces primary and secondary taxiways: primary taxiways take single letters (A, B), with double same letters (AA, BB) only after single letters run out, and A and B are recommended for the primary taxiways closest to the terminal where practical. Secondary taxiways (entrances, exits, connectors) take alphanumeric designations: the primary taxiway letter followed by a number (B2, C6), never a letter after the number (not B2A).
Avoid: number-only names (confused with runways), the letters I, O and X, descriptive words such as “inner” or “bridge”, and double different letters such as AB, because “Alpha-Bravo” can be heard as two taxiways (the AC allows limited exceptions for non-movement apron entries). Poor naming causes pilot confusion, ATC problems, wrong turns and longer taxi times.
AIRFIELD SIGN TYPES AND COLOURS
| Sign | Background / legend | Question it answers |
|---|---|---|
| Mandatory instruction | Red, white legend with black outline | Where must I stop or what is restricted? (holding positions, ILS/POFZ, approach/departure, CAT II/III, LAHSO, military landing zone, no entry) |
| Location | Black, yellow legend and border, no arrow | Where am I? (taxiway or runway) |
| Direction | Yellow, black legend, arrow | Which taxiway, which way? |
| Destination | Yellow, black legend, arrow | Where does this route lead? (supplementary only) |
| Information | Yellow, black legend, usually unlighted | Noise abatement, VOR checkpoint, other specialised pilot information |
| Boundary | Yellow, black legend or symbol | Am I leaving a protected area? (RSA/OFZ, approach/departure, ILS/POFZ, CAT II/III); normally used only at controlled airports where ATC asks for it |
| Runway distance remaining | White on black | Distance remaining |
Fast identification
- RED background = MANDATORY
- BLACK background = LOCATION (distance-remaining signs are also black, with white numerals)
- YELLOW background = DIRECTION / DESTINATION / INFORMATION / BOUNDARY
- BLACK + YELLOW STRIPES = TAXIWAY ENDING MARKER
SIGN DETAILS: ARRAYS, DESTINATION, ENDING MARKER, NO ENTRY
Arrays: left-turn designations go left of the location sign, straight-ahead/right-turn designations to the right (with exceptions). Direction signs sit where turns are common and intended and are not collocated with holding position, boundary or destination signs. Mandatory signs generally use no arrows.
Destination signs are optional, supplementary and should not replace standard location/direction signs, nor be placed on runways; they cover outbound routes (towards runways) and inbound routes (to aprons). Outbound signs show the departure runway designation and an arrow (e.g. 27 →); inbound signs use generic terms of at least three characters (APRON, CARGO, TERM). They are not collocated with location, direction or mandatory signs.
Taxiway ending marker: shows that the taxiway does not continue past a T-intersection; a frangible retroreflective barrier on the far side, recommended where excursion risk is high and other cues are inadequate.
No-entry sign: circle with a horizontal bar, placed on both sides of the taxiway before the restricted area (one left-side sign only where a safety assessment justifies it), useful on one-direction paths such as some runway exits; it does not replace the holding-position sign where that is required. Runway exit signs and acute-angle exits have specific criteria in AC 150/5340-18H.
L-858 SIGN TYPES (AC 150/5345-44L)
| Type | Use | Colour |
|---|---|---|
| L-858Y | Direction, destination, boundary | Black on yellow |
| L-858R | Mandatory / holding position | White on red (black outline) |
| L-858L | Taxiway and runway location | Yellow on black |
| L-858B | Runway distance remaining | White on black |
| L-858C | Taxiway ending marker | Yellow 45° stripes on black |
| L-858H | One-half distance remaining | White on black |
Signs may be lighted (internal illumination) or unlighted (retroreflective). A lighted sign has a housing, face, legend, light source or LED modules, driver, wiring and frangible mounting. Font and character sizes come from AC 150/5345-44, not the fabricator. Each sign is also specified by Size, Class, Style and Mode. At Part 139 airports AC 150/5340-18H calls for lighted mandatory, location, direction and distance-remaining signs; unlighted retroreflective signs can be an economical option elsewhere, with lighting prioritised for runway holding position signs.
SIGN SIZE, LOCATION AND INSTALLATION
| Size | Legend height | Panel height | Max installed height | Offset from usable pavement edge to near side of sign |
|---|---|---|---|---|
| 1 | 12 in (30 cm) | 18 in (46 cm) | 30 in (76 cm) | 10–20 ft (3–6 m) |
| 2 | 15 in (38 cm) | 24 in (61 cm) | 36 in (91 cm) | 20–35 ft (6–10.5 m) |
| 3 | 18 in (46 cm) | 30 in (76 cm) | 42 in (107 cm) | 35–60 ft (10.5–18 m) |
Signs are generally on the left side of the taxiway as seen by the approaching pilot, with explicit exceptions (geometry, conflicts, signs back to back, terrain). The top of the sign needs at least 12 in (30 cm) clearance from any part of the most critical aircraft, measured with its wheels at the pavement edge; if the maximum offset cannot give this, reduce the sign size. Size choice weighs visibility, clearance, space, jet blast, snow and ice removal and geometry, and all signs in one array use the same panel size. The middle of a sign array should be no more than 150 ft (45.7 m) from the taxiway centerline for lighted location/direction arrays, 125 ft (38 m) for lighted runway holding position signs and 60 ft (18.3 m) for unlighted signs.
At a runway holding position the taxiway location sign goes outboard of the holding position sign. Holding position signs go on the left, and also on the right where the holding-position width exceeds 150 ft (45.7 m), the marking does not run straight across, the position is close to a turn, or a risk assessment calls for it. No signs go between the holding position sign and the runway. The sign face is generally perpendicular to the centerline, or canted inward up to 30° where it helps legibility, and consecutive signs need at least 50 ft (15.2 m) between them and enough spacing to be read. Signs go on frangible supports (frangible point no more than 3 in / 7.6 cm above grade) on stable foundations that finish under 1 in / 25 mm above grade, with bonding and grounding per the project design.
Design order: geometry → designation → route analysis → sign need → location → array. Do not design signs before the route geometry.
ELECTRICAL AND CONTROL
Illuminated signs should give consistent illumination at each relevant edge-light brightness setting. Runway-related signs (mandatory, runway-holding location, ILS, CAT II/III, approach/departure, runway exit) should light when runway edge lights light; taxiway location, direction and destination signs when taxiway edge lights light. Simultaneous operation does not require the same circuit, and a dedicated sign circuit lets signs stay available while edge lighting is out for maintenance.
Sign power design should consider supply, load, inrush, brightness, driver arrangement, circuit grouping, protection, monitoring, voltage drop and environment. On a series circuit the sign is normally fed through an isolation transformer or series-circuit power adapter unit installed below ground in an L-867 light base, with power passing through breakaway connectors in the frangible coupling (AC 150/5340-18H para 1.17; details in AC 150/5340-30). The sign Style sets its power input, so match it to the circuit type. See Note 09 for the series-circuit side.
Stop bars
A stop bar is a lighting system, not a painted line. A runway holding position can combine marking, mandatory sign and stop bar: marking + sign + lighting. Blue taxiway edge lights are separate from the yellow edge marking.
MAINTENANCE AND FAULT-FINDING
Lighted sign
Electrical (supply, driver, wiring, protection), optical (light source, uniformity, dark spots), mechanical (housing, face, mounting, frangible support).
Unlighted sign
Retroreflective surface, legend, scratches, fading, dirt, night visibility.
Sign face
Dirt, dust and oil reduce contrast and reflectivity; clean with an approved method.
Markings
Centerline, edge, hold lines, shoulder, surface signs: colour, geometry, wear, rubber contamination.
| Problem | Check |
|---|---|
| Sign physically fine but dark | Supply → protection → control → driver → light source → internal wiring |
| Partly dark sign or dark patches | Failed LED module, driver or current imbalance, wiring, loose connector, moisture, diffuser, uneven ageing |
| Wrong taxiway identified | Location sign, designation, placement, surface-painted location marking |
| Wrong turn | Direction sign, arrow, designation, centerline geometry |
| Pilot overshoots holding point | Mandatory sign, hold marking, enhanced centerline, stop bar |
| Repeated confusion at an intersection | Geometry, designations, placement, array, centerline, lighting, destination signs, surface supplements |
Failure impact: location sign = position uncertainty; direction sign = route uncertainty; mandatory sign = holding uncertainty. A worn hold marking is not made good by the sign. In low visibility pay extra attention to centerline lights, signs, stop bars, hold markings, geographic-position markings and sign illumination.
PROCUREMENT, FAT AND HANDOVER
Do not order “Taxiway sign – Qty 20”. Specify: L-858 type + function + legend + size + class + style + lighted/unlighted + mounting + electrical requirements + frangibility + standard.
Internally illuminated airport taxiway sign Type: L-858Y | Function: Direction | Legend: A ← Legend colour: Black | Background: Yellow Size: 1, 2 or 3 per approved design Class / Style / Mode: per AC 150/5345-44L and circuit type Mounting: frangible support Lighting: LED | Power: per approved AGL design Compliance: applicable FAA / project specification
FAT covers appearance (dimensions, finish, legend, colour), electrical, optical (illumination, uniformity, legend visibility), mechanical and documentation. Handover should include the designation plan, sign schedule and location drawings, marking layout, circuit drawings, cable route, power distribution, final legends, inspection and test records. Compare as-built marking and signs against the approved drawings, and complete a night inspection.
| Sign ID | Location | Type | Legend | Function | Circuit |
|---|---|---|---|---|---|
| S-01 | TWY A/B | L-858L | A | Location | SC-01 |
| S-02 | A/B int. | L-858Y | B → | Direction | SC-01 |
| S-03 | RWY hold | L-858R | 27-9 | Mandatory | RC-01 |
| S-04 | Apron | L-858Y | 27 → | Destination | TC-01 |
Example sign schedule only; IDs and legends are project-specific.
COMMON MISTAKES
Wrong sign colour
Yellow/black where red/white mandatory is required.
Location vs direction confusion
Location signs have no arrow.
Wrong runway designation
Check against the approved design.
Unneeded destination signs
Only where standard signs are not enough.
Side, clearance, jet blast, size
Check exceptions, aircraft clearance and wind loads.
Rigid support
Frangibility is required where specified.
Wrong centerline or edge marking
Continuous edge where crossing is intended; solid side of hold marking on the wrong side.
Missing enhanced centerline; renaming without updating everything
Update signs, markings, drawings and ATC data together.
QUICK REVISION
Remember
- Centerline yellow · edge double yellow · hold line two solid + two dashed (solid on holding side)
- Hold line patterns: A = runway · B = ILS/POFZ and approach/departure · C = taxiway/taxiway
- RED/white = mandatory · BLACK/yellow = location · YELLOW/black = direction, destination, information, boundary
- Surface-painted signs supplement elevated signs
- Signs left side, 12 in clearance, frangible
- L-858Y / R / L / B / C / H
- Marking + sign + lighting = complete taxiway guidance
WHERE AM I? -> location sign WHERE DO I GO? -> direction sign WHAT DESTINATION? -> destination sign WHERE DO I STOP? -> mandatory sign + hold marking (+ stop bar) WHERE IS THE PATH?-> centerline + lighting
EXAM / INTERVIEW QUESTIONS
What colour is a normal taxiway centerline? Edge? Shoulder?
Yellow for all three.
What is an enhanced taxiway centerline?
A yellow centerline with parallel dashed yellow lines each side before a runway holding position, up to 150 ft (45.7 m).
What is a continuous edge marking? Dashed?
Double continuous yellow, where the outside is not for aircraft; broken double yellow where adjoining pavement may be used by aircraft.
What is the runway holding-position marking?
Four yellow lines, two solid and two dashed, with the solid lines on the holding side.
What does the runway holding sign add to the marking?
The marking shows where to stop; the sign shows what runway or protected area it is for.
What is the ILS holding marking?
Two solid yellow lines 2 ft apart with connecting pairs at 10 ft spacing.
What does a location sign tell the pilot? Its colour?
Where the aircraft is; yellow legend and border on black, no arrow.
What is a direction sign? Its colour?
Shows which taxiway and which way to turn; black on yellow with an arrow.
What colour is a mandatory sign?
White legend with black outline on red.
What is a destination sign?
Supplementary guidance towards a remote destination; yellow with black legend and an arrow.
What is an information sign?
Supplementary aeronautical information, black on yellow, typically unlighted.
What is a taxiway ending marker?
A frangible retroreflective marker showing the taxiway ends at the intersection (L-858C).
What is L-858Y? L-858R? L-858L?
Direction/destination/boundary; mandatory/holding; taxiway and runway location.
What are L-858B and L-858H?
Runway distance remaining and one-half distance remaining.
Which side of the taxiway do signs normally go?
The left side as seen by the approaching pilot, with exceptions.
What minimum clearance is needed above the sign?
12 in (30 cm) from the critical aircraft, per AC 150/5340-18H.
Does a surface-painted sign replace the elevated sign?
No; it supplements it.
Must signs share a circuit with edge lights?
No; they must operate simultaneously but not necessarily on the same circuit.
What do you check on a dark sign?
Supply, protection, control, driver, light source, internal wiring and monitoring.
Is a stop bar a marking?
No; it is a lighting system.
FINAL STUDY TAKEAWAY
Markings show the surface path, signs give coded navigation information, and lighting makes the guidance visible. Study them as one system: geometry → designation → markings → signs → lighting → control → pilot navigation.
Taxiway guidance = centerline + edge + holding markings + location + direction + mandatory + destination signs + taxiway lighting + stop bars + control + maintenance + correct designation.
ENGINEERING & EXPERT NOTES
Legend Accuracy Is a Safety Item
ContentCheck each sign against the approved layout before installation and after any change.
Inspect Seals and Drainage on Sign Enclosures
ReliabilityMoisture damages drivers and optics. Include seals in routine checks.
Measure Brightness and Legibility
PhotometryA sign that is lit can still be hard to read. Verify luminance and condition.
Check Mounting and Frangibility
MountingInspect foundations and breakaway features after impacts or work nearby.
REFERENCES & FURTHER READING
These notes are a study aid. Verify details against the primary sources below.
| # | Source | Use it for |
|---|---|---|
| 1 | FAA AC 150/5340-18H – Standards for Airport Sign Systems (30 Sep 2024) | Sign siting, design, installation and operation. |
| 2 | FAA AC 150/5340-1M – Standards for Airport Markings (2019, consolidated with Change 1, Dec 2020) | Runway, taxiway and apron markings. |
| 3 | FAA AC 150/5345-44L – Specification for Runway and Taxiway Signs (30 Sep 2024) | L-858 types, lighted and unlighted signs. |
| 4 | FAA AIM Chapter 2, Section 3 | Marking and sign descriptions. |
| 5 | FAA AC 150/5340-30J – Design and Installation Details for Airport Visual Aids | Taxiway lighting and stop bars. |
| 6 | ICAO Annex 14, Volume I – Chapter 5, visual aids for navigation (markings, lights, signs) | International requirements used at Indian aerodromes. Check the edition and amendment in force and DGCA requirements. |
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