Airfield Signage

Airfield signage is the set of illuminated signs that give pilots explicit, readable information about position, required action, and direction on the airport surface. Where lighting colour and configuration communicate implicitly (blue edge, green centreline, red stop bar), signage spells it out directly — "Runway 09/27", "Hold Short", or a directional arrow toward a specific taxiway.

Signs work alongside taxiway and runway lighting rather than replacing it — together they remove the ambiguity that colour and position alone can't always resolve, particularly at complex intersections.

Airfield signage's purpose is to remove the ambiguity that lighting colour and position alone can leave unresolved, especially at complex intersections where a pilot needs to know not just that they've reached a decision point but exactly what that point requires of them — which runway they're on, whether they must hold, which taxiway leads where. Because a misread intersection or a missed hold-short instruction can lead directly to a runway incursion, the standardised colour-and-text convention (red/white for mandatory, yellow/black for location, black/yellow for direction) exists so a pilot can identify a sign's category and act on it correctly even under time pressure or reduced visibility, without needing to fully parse its text first.

Airfield signs are positioned at taxiway intersections, holding points, and other locations where a pilot needs explicit confirmation:

• Mandatory Signs: Instructions that must be followed — e.g. runway holding position, no-entry, or category boundary signs. Typically white text on a red background.
• Location Signs: Identify the taxiway or runway the aircraft is currently on. Typically yellow text on a black background.
• Direction Signs: Indicate the taxiway(s) leading away from an intersection, with directional arrows. Typically black text on a yellow background.
• Destination Signs: Indicate general destinations such as the apron, cargo area, or a specific runway, often combined with direction signs.

Signs are positioned according to the specific information they convey — mandatory and location signs at the boundary of the intersection or holding position they mark, direction signs set back far enough from the intersection to give a pilot time to read and react to them before committing to a turn. Each sign is mounted on a frangible base set alongside the pavement rather than on it, positioned clear of aircraft wingtip and engine clearances while remaining close enough to the taxiway edge to be read from the cockpit at typical taxi speeds. Sign panels are oriented so their face is perpendicular to the expected line of sight of an approaching aircraft, since a sign angled away from the pilot's viewing direction loses much of its legibility even when correctly illuminated. Power and control cabling runs back to the same series circuit or a dedicated sign circuit serving that area of the taxiway network, with internal illumination wired so sign brightness can be stepped in coordination with the surrounding taxiway lighting.

Illuminated airfield signs are internally lit, either by a series-circuit-fed transformer/lamp arrangement similar to other AGL fixtures, or increasingly by LED modules fed at low voltage through their own isolating transformer on the primary series circuit. Legend, colour and fascia design are all specified so that the sign remains legible under the same lighting and visibility conditions the rest of the AGL system is designed for.

Key functional aspects include:

• Colour Convention: The red/white (mandatory) vs. yellow/black (location) vs. black/yellow (direction) colour pairs are internationally standardised so a pilot can read a sign's category before reading its text.
• Photometric Performance: Legend contrast, luminance and uniformity are tested in the same way as other AGL fixtures, since a sign that can't be read in fog defeats its purpose.
• Mounting and Frangibility: Signs near runways and taxiways are typically mounted on frangible fittings for the same safety reasons as approach lighting structures.
• Electrical Supply: Fed from the same series circuit family as adjacent lighting, so sign and lighting intensity can be coordinated together.

Illuminated signage carries no independent control logic — a sign's lamp or LED module is wired into the same series circuit family as the taxiway or runway lighting it sits alongside, so its intensity step is set by whatever the ALCMS or tower has already commanded for that circuit rather than by any separate decision for the sign itself. The isolating transformer and fault-detection principle are identical to any other AGL fixture on the loop.

Sharing a circuit with adjacent lighting is a deliberate coordination choice, not a limitation: it guarantees a sign's legend is always as bright, relative to the surrounding lighting, as the airfield's overall visibility conditions require, without needing a second control channel just for signage.

An illuminated sign is built as a shallow, weatherproof box housing the internal light source behind a translucent panel bearing the legend, so the message reads by transillumination rather than reflected light. The fascia panel is typically a UV-stable acrylic or polycarbonate sheet, screen-printed or vinyl-masked with the legend and background colours to the internationally standardised colour pairing for its category, and gasket-sealed into the housing frame to keep moisture off the internal optics. Inside, either a row of halogen lamps or an LED array (fed at low voltage through its own isolating transformer on the primary series circuit) sits behind the panel, with a diffuser or reflector arrangement chosen to spread the light evenly across the legend rather than leaving hot spots around each lamp. The housing itself is die-cast aluminium or a corrosion-resistant composite, bolted to a frangible mounting base identical in principle to those used on nearby light fixtures, so the sign shears cleanly if struck without damaging the aircraft or destroying the sign's own wiring beyond the break point.