What is flasher synchronization?
Keeping every flasher head firing at the right instant, on the control unit’s trigger, so the ball of light runs smoothly down the centreline to the threshold.
Flasher synchronization is keeping every flasher head in step with the sequence. The flasher control unit holds the master timing and sends a trigger to each head, outermost first and nearest the threshold last. Each head charges its capacitor and fires only on the master’s timing signal, so the timing is common to every head and the sequence repeats at the same rate each cycle.
When a head is late, early or silent, the pattern shows it: the ball of light seems to stutter, jump or step back, or has a gap. Typical causes are a fault on the trigger line, a loose connection, a head whose capacitor is slow to charge, a wrong timing setting after work, or a fault in the control unit. Where a system has more than one flasher group, follow the manufacturer’s documentation on how they are timed together.
It matters because the flashers supplement the steady lights, they do not replace them: a smooth moving flash is easy to pick out in fog, haze or rain, and a ragged one loses much of that value. After any work on a head, a trigger cable or the control unit, watch the whole sequence from a safe position before handing back.
Frequently Asked Questions
Q1What is flasher synchronization?
It is keeping every flasher head in an approach lighting system firing at the right instant in the sequence. When the heads are in step, a ball of light runs smoothly down the centreline toward the threshold at the same rate every cycle. When one is out of step, the run jumps, stutters or has a gap.
Q2How are the heads kept in step?
The flasher control unit holds the master timing and sends a trigger to each head in turn, outermost first. A head does not free-run on a timer of its own: it charges its capacitor and fires when its trigger, or the synchronising signal from the master, arrives. So the timing stays common to every head, as long as the triggers arrive on time and every head is ready to fire.
Q3What does the pilot see when a head is out of step?
A head that fires late or early makes the ball of light seem to jump or stutter, and two heads firing in the wrong order make it appear to step backwards. A head that does not fire leaves a gap. The steady-burning lights still show the pattern, because the flashers supplement them and do not replace them.
Q4What makes a head go out of step?
Common causes are a fault or damage on the trigger line, a loose or corroded connection, a head whose capacitor is slow to charge or has failed, a wrong timing setting after work, or a fault in the control unit itself. The cause is found by checking the trigger at the head and the head's own control box, following the manufacturer's instructions.
Q5Does a small timing error matter?
The flashers are a supplementary cue, so a small error does not stop the pattern from being read, but it spoils the smooth run that makes the flashers easy to pick out in poor visibility. Faults are put right within the time allowed by the airport's maintenance plan and the authority's rules.
Q6How is the sequence checked?
By watching the whole sequence from a safe position, from outermost head to threshold, and confirming that the order is correct, the spacing is even and no head is missing. This is done after any work on a head, a trigger cable or the control unit. Faults are also reported to the control point or ALCMS, as set up for the installation.
Q7What is hazardous when working on it?
The flasher heads are capacitor-discharge units, so they hold stored energy after the supply is removed. Treat the circuit as live until it is isolated, locked out and proved dead under the permit-to-work, and discharge the capacitors as the manufacturer instructs before opening a head or cabinet. The structures stand in the runway protection area, so access and aircraft-movement control apply as for any approach lighting work.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.