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Airbus Strobes

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Airbus Strobes

Old 18th Feb 2009, 14:06
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Airbus Strobes

I know that Airbus wing strobes double flash together, hence how you can always tell an Airbus on approach. However a few nights ago an A321 departed LHR with the wing strobes double flashing on alternative wings, as in left then right and so on. Does anyone know why that would of been? I've never seen the lights flash like that before.

Btw I'm not a pilot so I apologize if this isn't worded very well.
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Old 18th Feb 2009, 14:46
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The wing and tail strobes each have their own power supply unit adjacent to the light. These power supplies are all supplied with 115 volt ac power from the same bus through the same relay.
They aren't synchronised so over time they will go out of sync with each other.
I'm surprised they normally flash at the same time, can't say i've ever watched one long enough to notice.
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Old 9th Mar 2009, 17:20
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I would like to differ on that!!! its got nothing to do with the power supplies and the 'Synchronisation' of the supplies,The Strobe Lights flash twice the rate of the beacons( I dont remember the exact rate per second), but our brain is unable to synchronise the optical illusion of two kinds of lights flashing at such a high rate, whereas in reality both the lights flash at a constant rate (with beacons flashing half the rate of strobes) and hence the strobes appear to flash 'twice' together !!! Its all in our BRAINS !!!!
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Old 9th Mar 2009, 21:45
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the strobe lights are synchronized with the beacon light when they are both switched on. indeed you will see a double flash from the strobes and then then the red flash from the beacon. the tail strobe light only flashes once.
it is possible that the red beacon light was switched off which would have caused the strobe lights to flash twice but with a different pattern as which you have described.
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Old 9th Mar 2009, 22:20
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The wing strobes do have a double flash - period. It is nowt to do with your brain or your big toe.

As a strobe power pack gets older, it loses it's ability to fire and hence they will either fire once, or fire out of sequence.

Our Whelen strobes on our RV fire 4 times - it is called a Comet Flash and when on the bench you can clearly hear the 4 discharges through the power pack.
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Old 10th Mar 2009, 01:23
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Airbus wing strobes double flash together
Maybe I need to clean my glasses, but it looks to me like they are single flashes by two separate globes on each wing tip. Each flash is separated by a few milliseconds.

I don't know how that explains the orignal poster's observation!
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Old 10th Mar 2009, 10:07
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Capt Bloggs is correct

From the AMM

Strobe Lights

The two forward facing strobe lights and the rearward facing strobe light flash at the same time at a rate of 55 +/- 5 flashes per minute. A second flash tube in the forward facing strobe lights flashes at a rate of 55 +/- 5 flashes per minute. This gives 110 +/- 10 flashes per minute in the forward direction and 55 +/- 5 flashes per minute in the rearward direction.
What I said earlier still stands, when they are switched on they are all powered at the same time from the same source. Over time with the tolerance of +/- 10 they will eventually stop flashing together.
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Old 10th Mar 2009, 11:59
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Hey Guys!!! No need to get all touchy about this !!!! here is the info straight from the manual:

Anti-Collision/Beacon Lights

The two anti-collision/beacon lights which do not rotate flash at a rate of 60 +/- 10 flashes per minute. Both lights give 360 degrees of horizontal, and 75 degrees of vertical diffusion.

B.
Strobe Lights

The two forward facing strobe lights and the rearward facing strobe light flash at the same time at a rate of 60 +/- 10 flashes per minute. Additionally a second flash tube in the forward facing strobe lights flashes at a rate of 60 +/- 10 flashes per minute. This produces 120 +/- 10 flashes per minute in the forward direction and 60 +/- 10 flashes per minute in the rearward direction.

Now if people read it with their minds open.....can see Strobes flash twice that of beacons and Airbus trainers in Toulouse actually prove it by specially mentioning and describing that our human brain is unable to synchronise the 2 different flashing lights at such a high rate so AIRBUS strobes appear to be flashing TWICE together!!! if you want a proof.....next time you are on an Airbus aircraft just put only strobes ON and then put only beacons ON and the put Both ON at the same time, you will know!!!

ITS NEVER TOO LATE TO LEARN SOMETHING NEW.....IF PEOPLE STOP ASSUMING THEY KNOW EVERYTHING!!!!!

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Old 10th Mar 2009, 12:09
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Fargoo, Mr Fixer....

Look at any Airbus with its lights on next time it's dark and you will clearly see that the two forward facing, wing-mounted strobes flash alternately (in other words, not at the same time). The rear-facing strobe only flashes once.

This in not an optical illusion.

Certainly both of the forward facing ones achieve a flash-rate of 55 per minute but each does so a fraction of a second apart. This is then followed by the illumination of the upper and lower "beacon" lights, a short pause and then the cycle commences again.

The +/- 5 flash "tolerance" will have no bearing on the synchronicity of the strobe's flash because, as you say Fargoo, they are all powered "at the same time from the same source". This would only be an issue if the two-forward facing strobes were powered from different sources.

All +/- 5 means is that one A320 may have strobes that each flash 57 times a minute, while its sistership's may only flash 54 times a minute - it's a manufacturing tolerance.

The AMM clearly states that the forward facing strobes combined produce twice the number of flashes as the rear-one. This number wasn't derived on the assumption that the human eye is being tricked!

Booksmarts are great but in this case? WYSIWYG.
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Old 10th Mar 2009, 13:22
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Strobes that are getting older can behave strangely. Especially if the strobes work on a capacitor principle. These get older, they get moisture in them over time,... so their fire rate will change over time. I've even seen strobes that were continuously on, and then suddenly flashed at a rate of 1 time per minute. Others stopped flashing during VHF transmit, and others just danced at their own pace.
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Old 10th Mar 2009, 15:44
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I'm not getting touchy you tpot

You're totally correct WYSIWYG , just though i'd stick up the MM. Even then both me and MrFixer end up with different no's

Maybe they do flash together and maybe the beacons have some dance with them too. We're all trying to answer the OP's original question , how do they get that far out of synch.

I didn't make myself very clear earlier - each strobe is powered from the same aircraft bus but has an individual power supply which takes that 115v ac and converts it. Hence, over time these power supplies will no doubt output to the light at slightly different intervals to their counterparts on the aircraft.



for the really sensitive among you, my first line was a joke
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Old 10th Mar 2009, 15:48
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Thanks Flyingins, agree on your reply!!! But I was mentioning what the Airbus instructors showed us in Toulouse, and I had to agree myself when they actually proved it!!!

And Piper19, yes I have seen lots of wierd behaving Strobes & Beacons just like the ones you mentioned.

WELL AS THEY SAY......IF THINGS DONT BREAK, WE ALL WILL BE OUT OF JOBS!!!
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Old 10th Mar 2009, 15:59
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FARGOO,

We both quoted the AMM but its to do with the effectivity, I didnt bother quoting all the effectivities which I assume might be similar to the ones you work on!!! as the MM gives different rates for different effectivities
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