How is an airfield sign installed?
A sign is set at a surveyed distance from the pavement and kept low, on a foundation that holds it steady but a mounting that breaks away if an aircraft strikes it.
A sign has to be read from a taxiing aircraft and yet stay out of its way. Installation is where both are achieved: the sign is placed at the right distance from the pavement and no higher than its limit, stands on a firm foundation, and is fixed through a mounting designed to break away.
1Position and height
The sign goes at its surveyed position on the layout, a set setback from the defined pavement edge to the near side of the sign. The setback depends on the aerodrome code number and on whether the sign serves a taxiway or a runway. The installed height must not exceed the limit for its legend height, so propellers and engine pods keep their clearance. Both are measured on site, not assumed.
2Foundation and frangible mount
A foundation or base can carries the sign and is set level. The sign's supports are fixed to it through a frangible coupling, a deliberate break point that gives way on impact. Annex 14 requires airfield signs to be frangible, so the mounting must not be stiffened, braced or fitted with substitute fixings, and the fixings are tightened to the manufacturer's torque.
3Power, earth and check
The sign is fed by cable from the series circuit through an isolating transformer. Cable and connectors are made up only with the circuit isolated, locked out and proved dead; the series circuit is never opened while the regulator is energised. The cable entry is sealed, and the structure is bonded to the earthing network with a flexible bond that does not bridge or restrain the frangible coupling. The sign is then checked for level, installed height, setback and face direction, and lit to confirm the legend is complete and even. Alignment, visibility, circuit, transformer and connector each have their own entries later.
| Stage | What is done |
|---|---|
| Set-out | Surveyed position, setback from the pavement edge and sign type taken from the layout |
| Foundation | Base placed and levelled, with the cable entry formed |
| Mounting | Frangible coupling and supports fitted, sign fixed to the manufacturer's torque |
| Connection | Cable, isolating transformer and connectors made up, structure bonded to earth |
| Final check | Level, installed height, setback, face direction, then a lit test of the legend |
Height limits
| Legend height | Face height (min) | Installed height (max) |
|---|---|---|
| 200 mm | 400 mm | 700 mm |
| 300 mm | 600 mm | 900 mm |
| 400 mm | 800 mm | 1,100 mm |
Setback from the pavement edge
| Code number | From taxiway pavement edge | From runway pavement edge |
|---|---|---|
| 1 or 2 | 5 to 11 m | 3 to 10 m |
| 3 or 4 | 11 to 21 m | 8 to 15 m |
Frequently Asked Questions
Q1Why must an airfield sign be frangible?
A sign stands close to the paved surface, so an aircraft can strike it. A frangible mounting is designed to break away on impact instead of resisting, which limits damage to the aircraft and the sign. Annex 14 requires airfield signs to be frangible.
Q2How high can an airfield sign be when installed?
The installed height is limited by the legend height. The limits are 700 mm for a 200 mm legend, 900 mm for a 300 mm legend and 1,100 mm for a 400 mm legend. Keeping signs low preserves clearance for propellers and engine pods.
Q3How far from the pavement edge is a sign placed?
It depends on the aerodrome code number and on whether the sign serves a taxiway or a runway. For code 3 or 4 the near side of the sign is 11 to 21 m from the taxiway pavement edge and 8 to 15 m from the runway pavement edge. For code 1 or 2 the ranges are 5 to 11 m and 3 to 10 m.
Q4What is connected when a sign is installed?
The sign is fed from the airfield series circuit through an isolating transformer. The cable enters through a sealed entry, joins the sign through connectors, and the sign structure is bonded to the earthing network. The circuit, transformer and connector each have their own entries later.
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