What is a sign mounting structure?
Everything between the ground and the housing: foundation, anchors, base plate, legs and a breakaway coupling. It holds a sign steady in wind and jet blast, and lets go cleanly if an aircraft strikes it.
A sign stands close to the runway or taxiway, so it must stay upright and readable in wind and jet blast, yet not be a hazard if an aircraft hits it. The mounting structure is what balances those two demands.
1Carry the load
A concrete foundation sits below ground. Anchor bolts tie a base plate to it, and two or more legs rise from the plate to the housing. Together they hold the sign at its design height and angle, so the legend faces the pilot squarely. A foundation that settles or an anchor that loosens lets the sign tilt or twist.
2Strong, but weak by design
Annex 14 asks for signs to be frangible and low. So the structure is built to resist weather, then to part at a frangible coupling near the base when struck. The housing and legs separate, and the foundation and base plate stay put. The coupling is covered in the next entry, Frangible mounting. Never swap it for an ordinary fastener or add extra bracing, as that can defeat the breakaway.
3Connect, bond and inspect
The supply cable rises through the foundation to the housing, and the sign is bonded to the earthing system with a slack, flexible lead that does not bridge or restrain the coupling. Check for tilt, loose or corroded fasteners, cracked couplings, a cracked foundation and any change in height or angle, and keep grass, soil and snow clear of the base.
| Part | Job |
|---|---|
| Foundation | Gives the sign a firm, level base below ground |
| Anchor bolts | Tie the base plate to the foundation |
| Base plate | Spreads the load and takes the legs |
| Legs | Hold the housing at the right height and angle |
| Frangible coupling | Parts at a set load if the sign is struck |
| Bonding point | Connects the sign to the earthing system |
| Cable route | Brings the supply lead up to the housing |
| Standard | Annex 14: signs must be frangible and low |
Frequently Asked Questions
Q1What is the mounting structure of an airfield sign?
Everything between the ground and the sign housing: the foundation, anchors, base plate, legs and the breakaway coupling. It holds the sign at the right height and angle and carries the wind load.
Q2Why does a sign need a foundation?
A sign must stay upright and aligned in wind and jet blast. A foundation with anchors gives the legs a firm base, so the sign does not tilt, twist or lean away from the pilot.
Q3If the structure is strong, why must it also break away?
Aircraft can strike a sign. Annex 14 asks for signs to be frangible, so the structure is strong for weather but is designed to part at a set point, usually the coupling, if hit.
Q4What should be checked on a mounting structure?
Look for tilt, loose or corroded anchors and fasteners, cracked or damaged couplings, a cracked foundation, and any change to the sign's height or angle. Follow the manufacturer's instructions.
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