What are control commands?
The instructions an authorised operator sends to switch, dim, select or reset airfield lighting — and how the system shows whether the equipment actually did it.
A control command is an instruction sent from the control system to the lighting equipment: switch a circuit on or off, select a brightness step, choose which circuits or mode are in use, or reset after a fault. It is sent by an authorised operator from the control position in charge, such as the tower or the maintenance control room, and passes through the ALCMS, which can check the operator’s authority, the equipment’s mode and any interlocks before the command goes out.
The key idea is that a command is a request, not a result. The result is confirmed by the status feedback (see Equipment Status): after a command, the status should change to match, such as Running at the new step. No change means no confirmation, whatever the button looked like. Commands can also be blocked on purpose: equipment in local mode ignores them, and an interlock can refuse an unsafe or conflicting combination. Because a command can energise a circuit, switching on or resetting is done only when the field is confirmed safe.
- Authorise. Only the operator in charge of control, with the right authority, sends it.
- Check. The ALCMS checks mode and interlocks, and the field must be known to be safe.
- Send. The command travels over the link to the CCR or field unit.
- Act. The equipment changes its output.
- Confirm. Read the status feedback and, where needed, verify by observation.
Control Commands Explorer
Pick a command to send
What happens REQUEST TO RESULT
How you know AND WHAT TO DO
Teaching simulation. Checks, messages and timings are illustrative; real systems behave differently.
Frequently Asked Questions
Q1What is a control command?
An instruction sent from the control system to lighting equipment, for example to switch a circuit on or off, select a brightness step, choose a circuit or mode, or reset after a fault. It is a request to the equipment, not a guarantee that the equipment has done it.
Q2How do I know a command worked?
By the feedback. After the command, the equipment's status should change to match, such as Running at the new step. If the status does not change within the expected time, the command has not been confirmed, whatever the button looked like.
Q3Why can a command be refused or blocked?
The control system can check authority, the control position in charge, the equipment mode and any interlocks before sending it. Equipment in local mode ignores remote commands, and an interlock can stop a combination that would be unsafe or conflicting.
Q4What should I do if a command gets no response?
Do not keep resending it. Check whether the equipment is in local mode, whether its status is still live, and whether the communication link is up. Then confirm the real state by another means before trying again.
Q5Is it safe to send a remote switch-on or reset?
Only when the field is confirmed safe. A command can energise a circuit that someone may be working on. Isolation and lock-off at the equipment under the work permit protect people, and screen flags alone do not.
Q6Who is allowed to send commands?
Only people with the right authority, from the control position that is currently in charge, such as the tower or the maintenance control room. Systems normally log who sent what and when, which is how a command can be traced afterwards.
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