External Strobe Light Timing Needs Tweaking

[mert4everlive 0]

It actually looks like this

 

 

[JRBarrett 3,070]

I have no hard and fast knowledge of how the wing/tail strobes are wired on a 777 specifically, but in my aircraft maintenance career on many aircraft models, I have found that the wing strobes in particular are often sequenced with each other. 

Whether the strobes are the older xenon gas-filled flash tubes, or the more modern high-intensity LED, they usually have power supplies external to the light which produce a high voltage pulse to fire the light. The wing strobe power supplies are typically interconnected so that the lights will flash simultaneously. The tail strobe power supply may (or may not) be synchronized to the wing strobes. I’ve seen it done both ways.

I have never seen any aircraft in which the red beacons are synchronized with the wing or tail strobes however. In the great majority of aircraft I have worked on, the two red beacons are completely independent of the white strobes, and of each other. 

The beacons may occasionally appear synchronized with the strobes if their timing patterns happen to line up at a given moment, but that will change over time.

The exact flashing sequence can vary from one aircraft to another, even within the same model series, depending on how old a given airframe is. Newly- manufactured airliners typically use high-intensity LEDs for both the red/green/white nav lights, and the white strobes and red beacons. Older aircraft may still have incandescent bulbs for the nav lights and gas flash tubes for the strobes and beacons. It is quite common to retrofit the new LED lights on older airframes during a C check, as the LEDs are much more reliable.

One has to be careful using HD camera videos to “prove” what the flash sequence is. Depending on the number of frames per second that the camera is capturing the video, strobe flashes in particular can be completely “missed” by the camera, as the flash duration is only a few milliseconds for gas flash tube type strobes. LED strobes stay “on” much longer each time they are triggered.

 

[anden145 2,285]

28 minutes ago, JRBarrett said:

I have no hard and fast knowledge of how the wing/tail strobes are wired on a 777 specifically, but in my aircraft maintenance career on many aircraft models, I have found that the wing strobes in particular are often sequenced with each other. 

Whether the strobes are the older xenon gas-filled flash tubes, or the more modern high-intensity LED, they usually have power supplies external to the light which produce a high voltage pulse to fire the light. The wing strobe power supplies are typically interconnected so that the lights will flash simultaneously. The tail strobe power supply may (or may not) be synchronized to the wing strobes. I’ve seen it done both ways.

I have never seen any aircraft in which the red beacons are synchronized with the wing or tail strobes however. In the great majority of aircraft I have worked on, the two red beacons are completely independent of the white strobes, and of each other. 

The beacons may occasionally appear synchronized with the strobes if their timing patterns happen to line up at a given moment, but that will change over time.

The exact flashing sequence can vary from one aircraft to another, even within the same model series, depending on how old a given airframe is. Newly- manufactured airliners typically use high-intensity LEDs for both the red/green/white nav lights, and the white strobes and red beacons. Older aircraft may still have incandescent bulbs for the nav lights and gas flash tubes for the strobes and beacons. It is quite common to retrofit the new LED lights on older airframes during a C check, as the LEDs are much more reliable.

One has to be careful using HD camera videos to “prove” what the flash sequence is. Depending on the number of frames per second that the camera is capturing the video, strobe flashes in particular can be completely “missed” by the camera, as the flash duration is only a few milliseconds for gas flash tube type strobes. LED strobes stay “on” much longer each time they are triggered.

 

Wow! I wish, I could give you 2 plusses for that answer, Jim. 

I was actually going to suggest, whether the timing of wing- and tail strobes, could be completely dependent on the age of airframe and equipment? Age of the actual electronics within the airframe, which controls the sequence. 

The timings probably starts being in sync, and as the airframe ages, wear and various conditions makes the timing off somehow? 

Edited April 22, 2018 by Anders Bermann

[JRBarrett 3,070]

1 minute ago, Anders Bermann said:

Damn! I wish, I could give you 2 plusses for that answer, Jim. 

I was actually going to suggest, whether the timing of wing- and tail strobes, could be completely independent on the age of airframe and equipment? Age of the actual electronics within the airframe, which controls the sequence. 

The timings probably starts being in sync, and as the airframe ages, wear and various conditions makes the timing off somehow? 

With the wing strobe power supplies, there will often be a cross-connection between the two, so that when one fires, it triggers the other to fire at the same instant.

The older gas flash-tube strobes require a pulse of several hundred volts to fire. The pulse is of very short duration, using high voltage but low current. The power supply is usually fed with 28 volts DC, and contains an inverter to step the voltage up to charge a capacitor to the level that will fire the tube. The flash rate is set by a timing circuit inside the power supply.

As the power supplies age, the timing can change. The age of the individual flash tubes has an effect too. The tubes have a finite life span. As they get older, it may take more and more voltage to trigger them. When a tube is near the end of its life, it may not flash every time it’s triggered, so even on an aircraft  where the two wing strobes are supposed to flash simultaneously, one or the other may not always flash at the same time as the other.

On aircraft with gas tube strobes, there is an inspection requirement driven (in the U.S.) by FAR 23.1401 or 25.1401 which the flash rate, and light intensity must be tested at regular intervals.

If you google “FAR 23.1401”, you can read all about it😁

LED strobes are different in that they are not “triggered” by a high voltage pulse. They simply turn “on” and “off” at intervals. LEDs use lower voltage and higher current than flash tube strobes.

[Ephedrin 418]

I have noticed that when I hold at a red light with my car behind another car of the same model and year the turn signal / blinker / how it's called??? isn't timed the same either.. you know this effect, when they light up simultaneous and then lose themselves again until a few sequences later they match up again... 

at revisions something can be changed, another charge of bulbs can take a little more time to flash... nothing is 100%

[JRBarrett 3,070]

10 minutes ago, Ephedrin said:

I have noticed that when I hold at a red light with my car behind another car of the same model and year the turn signal / blinker / how it's called??? isn't timed the same either.. you know this effect, when they light up simultaneous and then lose themselves again until a few sequences later they match up again... 

at revisions something can be changed, another charge of bulbs can take a little more time to flash... nothing is 100%

Exactly. The 777 family has been in continuous production for almost 25 years, and in that time, there have probably been many variations and iterations of external lighting, driven by the state of the art at the time a given airframe was delivered, and also by the requirements of the purchasing customer. I don’t think that it is possible to say that there is one “correct” definitive way for strobe lights to work on “all” 777s.

One of the aircraft I maintain is a 19-year-old Dassault Falcon 900. When the aircraft was brand new, it came equipped with old-style rotating red beacon lights - i.e., incandescent bulbs, with a motor-driven reflector that rotated to cause the beacon to “flash” from any given external vantage point.

A few years later, the rotating mechanical beacons were replaced with  gas-discharge flash tube models.

Now, we are pricing out replacing the beacons yet again with a new model that uses high-intensity LEDs.

[HUSSAR 272]

Thanks for your replies Jim, totally makes sense now that you mention it.  I was just thinking how far the devs have come, I'm down to posting about the synchronization of external lighting.