How does the ALCMS control signs?
The control system switches the signs on and sets their brightness; the message on a fixed sign stays on its panel.
Airfield signs — mandatory instruction signs and information signs (location, direction, destination) — are normally fed from a series lighting circuit, each sign through its own sign transformer. The ALCMS-to-signage link lets the operator switch that circuit on and off and set its brightness through the sign CCR, with circuit status and faults coming back.
Brightness matters because a sign must be readable in both darkness and daylight. The ALCMS does not change what a fixed-message sign says; that is set by its panel. It also helps to remember that circuit status shows the health of the whole loop: a single failed sign may not appear at that level and is found by inspection or by sign-level monitoring where it is provided.
- Switch. The operator turns the sign circuit on when conditions need it.
- Set brightness. The ALCMS selects an intensity step for the conditions.
- Drive. The sign CCR sets its current and each sign lights through its transformer.
- Monitor. Circuit state, current and faults return to the ALCMS.
Frequently Asked Questions
Q1What is the ALCMS-to-signage link?
The control and monitoring path from the ALCMS to the airfield sign circuits. The ALCMS switches the signs on and off and sets their brightness through the sign CCR, and receives circuit status and faults back.
Q2What does the ALCMS control on a sign?
Its power and brightness. For fixed-message signs, what the sign says is set by its panel and is not changed from the control system.
Q3How are signs powered?
Signs are typically fed from a series lighting circuit, each through its own sign transformer, so the CCR holds the current while each sign takes its share of the loop.
Q4Why does brightness matter for signs?
A sign that is too bright in darkness or too dim in daylight is hard to read. Brightness is stepped to suit the conditions, so pilots can read it comfortably and clearly.
Q5Will the ALCMS show if one sign has failed?
Not always. Circuit status shows the health of the whole loop, and a single failed sign may not show at that level. It is found by inspection or by monitoring, where the system provides it.
Q6Can signs have changing messages?
Some airports use variable-message signs, which need data as well as power. These depend on the specific equipment and design, so they are outside this general description.
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