What is a sign foundation?
The concrete base under an airfield guidance sign. It fixes the sign’s position, height and facing, so it has to be right before the concrete cures.
A sign foundation is a concrete pad or footing (or a level base can) that supports an airfield guidance sign. Anchor bolts set into it carry the sign’s frangible coupling, with the legs and housing above it, and a conduit brings the supply cable up to the sign with enough slack to part cleanly.
It is a civil interface because it is excavated and poured with the civil works, usually in turf beside a taxiway or runway. Its position, setback, facing, top level, anchor-bolt layout, cable entry and earth provision must match the signage layout and the sign’s mounting, and be agreed with the AGL team before the concrete cures. The setback depends on the aerodrome code number and on whether the sign serves a taxiway or a runway, and the installed height must stay within its limit. After a strike the foundation stays in the ground, ready for a new sign.
Pad or footing carrying a guidance sign on frangible legs, set for position, facing and height.
Small footing carrying an elevated light on a frangible coupling.
Frequently Asked Questions
Q1What is a sign foundation in airfield ground lighting?
A concrete base, usually a pad or small footing, that supports an airfield guidance sign. Some signs stand on a base can set level instead. Either way it holds the anchor bolts for the sign's frangible coupling and a conduit that brings the supply cable up to the sign.
Q2Why is a sign foundation a civil interface?
It is excavated and poured with the civil works, usually in turf beside a taxiway or runway. Its position, setback, level, facing and anchor bolts must be set to the signage layout and agreed with the AGL team before the concrete cures.
Q3Why do sign position and facing matter so much?
A sign is only useful if the pilot can read it from the correct approach, at the correct distance and angle. Errors in position or facing are hard to correct after the concrete cures, so setting out and template checks are important.
Q4Why are sign legs frangible?
Annex 14 asks for signs to be frangible. A coupling or weakened section just above the base is the break point, so the sign separates and falls clear while the foundation stays in the ground. Nothing should stiffen it, so grout, bracing or rigid conduit must stay clear.
Q5How does the conduit work with a sign foundation?
A conduit rises through or beside the footing so the supply cable reaches the sign's cable entry without being exposed. The lead is left with enough slack, commonly through a separable connector, so it can part if the sign is struck. The isolating transformer and connectors sit in the base can or sign base, and provision is made for the earth bond.
Q6Where are the requirements defined?
FAA AC 150/5340-18 covers sign systems, AC 150/5345-44 covers sign equipment, AC 150/5340-30 covers installation and foundation details, and ICAO Annex 14 covers sign placement and frangibility (see also ICAO Doc 9157 Part 6). Confirm against the current edition and the manufacturer's data.
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