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Laser threat defence

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Laser threat defence

Old 16th Feb 2016, 13:24
  #1 (permalink)  
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Laser threat defence

In light of the news on Monday about a [email protected] attack on a Virgin 744, a few of us have just spent our lunch hour chewing over the issue.

Apart from the usual sentiments involving locking up the perpetrators and throwing away the key, we were asking ourselves whether there's any technology that could be used to protect flight decks against [email protected] light?

Offhand, I can't think of anything - filtered lenses exist, but they're only effective if you know what frequencies you're designing for. Block the windscreens and go IFR immediately? - would work but degrades lookout immediately so contra safety for other reasons.

Does anybody have any bright ideas?

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Old 16th Feb 2016, 16:19
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How about modifying existing side window sunshades? Not sure how many attacks are aimed at the forward windows as opposed to the side views though....also how much visibility the crew would have once the shades are in place?
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Old 16th Feb 2016, 17:20
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My favourite tactic is to swich the external lights off as soon as I see someone fiddeling around with this things. Yes, it is against the ANO but as a commander I can take all measures.... you know the stuff. Worked a treat so far. What the warrior can't see, he can not attack.
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Old 16th Feb 2016, 17:26
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Maybe something using the technology of this welding helmet would do: https://www.youtube.com/watch?v=L5bMlI9ZHyY
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Old 16th Feb 2016, 17:29
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In a previous job, hovering over and illuminating the perpetrator with the 30 million candlepower Nitesun used to give them a bit of a hint.

Blue flashing lights outside the front door was the second hint that a slight misjudgement on their part had been made.
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Old 16th Feb 2016, 18:31
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Seeing as we live in an age of [email protected] guided weapons would it not be possible to install reflective devices on the aircraft which would reflect the beam straight back at them?
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Old 16th Feb 2016, 19:06
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would it not be possible to install reflective devices
Maybe. But that might give the miscreants some feedback on their aim. And some people might just get a kick out of being 'flashed back' by a passing airplane.

Blue flashing lights outside the front door
If that works reliably. What is the arrest rate for [email protected] incidents? Unless you are dealing with some abject morons who keep lighting up successive planes, by the time one is reported, they have turned their pointer off and gone inside.

Something needs to be done to ensure that detection and arrest is nearly certain. Possibly a detector (camera) and GPS position that could automatically forward source location data to authorities on the ground. An iPhone/Android app on a phone positioned to look out the cockpit window might be sufficient.
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Old 16th Feb 2016, 20:42
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I'm sure that something along the lines of an electronic auto-dimming welding mask glass could be made to work in cockpit windows. But it'd have to be totally reliable; after all you wouldn't want it going dark by mistake, might make the landings tricky...

It would be sad if something like that became the only solution to the problem (instead of import controls, prosecution of vendors and manufacturers, policing, etc).

It's well known that pilots are getting hurt. Are there any reports on passengers and cabin crew getting hurt? I guess that side on illumination isn't going to be as steadily aimed, but would probably still be damaging.

I'm sure there are systems in the military that can pinpoint the origin of [email protected] light. Of course, civil aviation isn't warfare so the Geneva convention does not apply; you could have automatic gun aiming/firing integrated with such a system. It could be a specific variant, e.g. 747-400-130...

Illustration of the problem

Someone I worked with was involved in buying items like [email protected] pointers from manufacturers in a certain large Far East Asian country. At one place he was shown a selection of [email protected] pointers, and the labels on them (an indeed the demonstration) made it quite clear that the power output was far in excess of what was safe or legal in Europe.

When he explained this to the company and said he couldn't possibly buy them, their response was "no problem, we'll change the labels". Says it all really.
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Old 16th Feb 2016, 23:46
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I'm pretty sure I've seen [email protected] protection glasses that work by blocking a very specific wavelength. Because they take such a small chunk out of the spectrum, they have little effect on other light sources. Something like that might work for windshields. (I guess you might need to block more than one frequency based on the types of [email protected] that need countering, but probably not more than a few.)

Or maybe you could use the welding helmet technology with a trigger that responds only to very specific frequencies, so the windshield (hopefully) wouldn't go opaque with each lightning flash.
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Old 17th Feb 2016, 00:34
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Laser Pointers - The Maths

I tried to post some analytical numbers about this in the other thread, but I mixed in some of my conjectures and opinions and it seems they upset people, so my posts were deleted and I was locked out of that thread.

I think the analysis is still worth an airing, and I’ve had some PMs asking for the details again. So I thought I would have another go, but this time sticking solely to the analysis and leaving my opinions out of it in the hope that no one feels it necessary to censor it again. So for what it’s worth…

Laser pointers – the maths:

Assume airliner flying at 8,000 feet.

Assume that to be visible to the pilot the ground level source must be no more than 30 degrees below the horizon.

Therefore the distance between source and target is 8,000/Sin(30) feet = 16,000 feet: let’s call it 3 miles.

[email protected] dispersion of 2mrad (0.06 degrees) at 3 miles gives a beam width at the target of roughly 10 metres (generous number).

That same number tells us that to keep any part of the beam impinging on the eye of the pilot needs the [email protected] to be within 0.06 degrees of the nominal target. For those with target shooting experience – this is the equivalent of a six inch grouping at 100 yards (not hard to achieve with a rifle while lying prone, but rather optimistic with a pistol held in one hand while standing up).

The target is moving, of course, but at that range it moves quite slowly.
Of course if we consider the low-level case on approach at 300 feet the range becomes 600 feet and the beam diameter becomes four and a half inches, but the targeting accuracy (where the “target” is a small point like the pilot’s eye) is actually the same, although the target is moving much faster across the sights.

According to the open sources [lots of them; the wiki page is the most easily found and digested] the power density required to cause retinal damage for [email protected] in the visible spectrum (say 400-800nm) is around 2mW/cm^2 for a 10 second exposure, 4mW/cm^2 for a 1 second exposure or 7.5mw/cm^2 for a 0.1 second exposure. So the question becomes what source power is required to achieve those power levels.

The beam diameter at 3 mile range was 10 metres. So the beam area is 785,500cm^2. If we assume even power density across the disk that means that to achieve a damaging power density for a 10 second exposure needs a 1500W [email protected], for a 1 second exposure this becomes a 3000W [email protected] and for a 0.1 second exposure it would need a 5,800W [email protected] Note that all three of these are more than three orders of magnitude (ie a thousand times) more powerful than the worst of the “illegal” [email protected] pointers being discussed, and six over orders of magnitude (ie over a million times) more powerful than the standard [email protected] pointers people like me use in lecture theatres. KiloWatt [email protected] are not hand-held devices.

For the 300 foot case it’s a bit different. At this range the beam diameter is only 11.5cm, so the disk area is 104cm^2. The [email protected] power to achieve the damaging exposures then becomes 0.21W, 0.42W and 0.78W (or 210mW, 420mW and 780mW if you prefer) for the 10 second, 1 second and 0.1 second exposures respectively. “Illegal” [email protected] pointers with *claimed* powers up to around 1watt can be bought from overseas [from the UK], so if someone can target them accurately enough they certainly could represent a risk of eye damage to the pilots of aircraft in the final few hundred feet on approach, and less so on departure (simply due to the angles involved).

These rough calculations ignore the attenuation effects of the cockpit glazing and the atmosphere. And the latter should not be overlooked, because visible [email protected] are just light – haze, cloud, dust/smog will block a [email protected] just as much as the reduce visibility. Visible light [email protected] don’t “burn through” haze and cloud until you get to power levels of tens or hundreds of kilowatts, that’s why jet fighters still have guns and missiles instead of [email protected] weapons and even the anti-satellite [email protected] concepts need [email protected] so large and powerful that they need an airliner to lift them and they need to be carried up to over 30,000 feet to get to air that is clear enough not to disperse the beam.

Finally, this analysis only considers the danger of eye-damage from [email protected] The distracting flash will still be visible, assuming the target can be held accurately enough, at both the ranges considered.

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Old 17th Feb 2016, 00:49
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Beam diameter.

PDR- From where does the beam angle spec come? What class of [email protected] have the .06 degree angle. Do cheaper and more expensive models have different angles?

Last edited by jack11111; 17th Feb 2016 at 04:07.
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Old 17th Feb 2016, 03:22
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Without going into details that may help the bad guys, I think you need to take a look at the actual beam parameters from a moderate cost 1 watt [email protected] pointer. Your required [email protected] power estimate for damage at higher elevation is off to the high side by a huge factor..

I just ran your numbers thru a professional beam safety program, and if one small beam detail is improved by a factor of 10, the 1 Watt [email protected] has a Nominal Ocular Hazard Distance far longer then your giving it credit for.

Especially if the inadvertent viewer is wearing eye glasses, and if the pointer user has added, or purchased a certain common modification.

However, I'm glad that your attempting the math instead of just repeating the common assumptions and rumors that are out there.

I work with laboratory [email protected], and [email protected] display projection systems for a living.

The real answer is to convince the Chinese government to stop the dumping of extremely low cost [email protected] onto the international market.
These low cost, hand held, [email protected] are a huge cash cow for Chinese optics companies. Most of which have some fairly shady owners, and have long been dumping optical parts at below market value.

Most of the time they are imported under fraudulent labeling to get around Customs...

As I work with Quality American and European systems, I can assure you these low cost [email protected] have taken a toll on the income, and sanity of legitimate [email protected] users. Now they are slowly creeping into the cosmetic medical device market, via on-line marketing.

And Pilots, one tip from a [email protected] professional. Avoid a possible secondary effect. Do your best NOT to rub your eyes after an inadvertent [email protected] strike. A bright [email protected] strike may strain muscles in the eye. Then if you drag a dirty hand thru the eye, you run a strong risk of pulling a muscle or irritating the soft tissue.

I got my start in [email protected] doing [email protected] shows. The low cost [email protected] pushed many of us who had professional gear, who obtained the required permits, and insurance for outdoor shows out of business. Most of those low cost [email protected] users are totally unaware or ignoring the fact that they need permits for un-terminated [email protected] shows in airspace. Filing the paperwork generates NOTAMs, and there is a lot of math required to ensure safety compliance. That means that the companies who still try to be legal must turn down a lot of potential customers, as there is a delay, and mandatory review period with the local agency.

Most of the time, if the green 532 nm wavelength is blocked, that takes care of 90% of the offenders. However when you start getting into multiple wavelength blocking filters, the optical transmission of non-laser light goes way down. If you block the needed red band, you loose viewing much of the aviation standard red and green lighting.

I've been reading PPRuNe as a outsider for years, sorry that my first post has to be on such a disgusting topic.

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Old 17th Feb 2016, 07:47
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Excellent analysis and gives serious food for thought. Given the number of attacks reported (and I have a strong suspicion there is actually significant underreporting) it would be helpful if the authorities issued some guidelines. PDR1's numbers suggest the risk decreases with height and above 10,000 feet on his numbers it looks low. But on final approach it could be significant. It appears you cannot reliably assess the power or exposure. But one option might be for a recommendation to get a medical check if targeted on final approach etc. Either way despite a little ill humour/stupidity that always seems to occur I think the wider discussion on this topic has been very helpful. Thanks to PDR1 and thumbs up to Scroggs.
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Old 17th Feb 2016, 08:24
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I like Hahn's idea. I have been lasered five times so far, twice in the cruise. Trouble is these idiots can look on flight radar and listen to our RT and score a 'bingo' when we report the [email protected]

I was once lasered on the ramp by a passenger sitting in the aircraft next to us !?! I kid you not.

Thanks PDR1, very interesting analysis. The chances of retinal damage would appear to be low?
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Old 17th Feb 2016, 09:26
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The chances of retinal damage would appear to be low?
Just to caveat this:

I am an engineer - not a doctor and not a magician, so all I will ever talk about is whether there is a risk that received power levels approach or exceed the values that SOMEONE ELSE has published papers saying they are dangerous.

So I cannot say "The chances of retinal damage when lasered above x,000 feet are low" - all I can say is that "The indications are that when lasered above x,000 feet the exposure won't exceed the values which the published papers say will cause retinal damage".

Now based on the sums I did last night the indications are that the risk of the retina receiving power levels above that threshold from a ground-based [email protected] pointer while flying above (pick a number - let's say 5,000 feet) is probably very, very low, but the risk at low level (again, pick a number - I choose 500 feet) is probably high enough to be a concern. But it would still require very clear air and probably require illegal devices and very accurate targeting.

It got late last night and I didn't finish what I wanted to say. So to continue - why did I mention the 10sec/1sec/0.1sec exposure times? Well when I first raised the issue of the targeting accuracy needed[1] in the thread I'm now excluded from it was countered by the suggestion that the beam wasn't "aimed" but "waggled about" [with some gratuitous suggestions about the waggler being drug-crazed, and maybe even a Trump supporter]. So again I did some math to evaluate this which was deleted because I included opinions. So I'll try again:

If someone has a pointer and is just "waving it about" the angular rates are likely to be of the order of more than 60 degrees per second (try it). Based on data from targeting trials (not public domain - sorry) for someone trying to aim at a device without any sights the "shake rate" is likely to be in the region of 20 degrees per second, dropping to 10 degrees per second for plain sights (people can get much better than this with telescopic sights and lots of practice, but neither has been suggested for morons lasering aeroplanes).

So what does that mean? Well for the aeroplane at 8,000 feet and three miles range a 10deg/sec "waggle" translates into the beam moving from side to side at 2,800 feet per second. We said the beam would be 10m (lets call it 33 feet) diameter, so any single point (like an eyeball) will only be within the beam for 12 milli-seconds: 0.012sec or one eighth of the fastest "flash" case I discussed in the previous post. So even if we pick some very pessimistic assumptions (clear air, high power, good [email protected] and an aimed [email protected] with sights) we are still many orders of magnitude too small to get near these published damaging power values.

Looking at the 300 foot case it suggests that the seemingly "dangerous" values mentioned above need to be divided by eight for a real-world case - or in other words the danger threshold power values are closer to 1.7W, 3.4W and 6.25W (or 1700mW, 3400W and 6250mW if you prefer) for the 10 second, 1 second and 0.1 second exposures respectively. We're start to get up to power levels which are harder to find on the open market (or even ebay!) even for the low-level case. Although the flash-distraction would still be an issue of course, and I can't find any particularly digestible authoritative data on the power levels at which flash after-images become persistent for more than a few seconds so I can't include that in the anlysis.


[1] Where someone said "laser pointers are used to point at stars, so obviously it isn't a problem" - huh? If you pointed a [email protected] pointer at the nearest star it would be 9.4 years before you saw the dot even assuming you were pointing it in the right place! Do people never think about what they are saying??
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Old 17th Feb 2016, 10:55
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PDR, you seem to be hooked on actual damage to the eye rather than temporary blinding/light spots and distraction. I can temporarily blind someone with a torch.

I will say again when I was subject to a [email protected] attack I got a brief flash across the eyes and that was enough to render my eyesight essentially useless for several minutes. Don't you consider that dangerous?
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Old 17th Feb 2016, 11:14
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What height were you at?

I have been flashed with these things at 500ft in a helicopter and had no loss of sight at all, just annoyance.
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Old 17th Feb 2016, 11:28
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Twice. First at about 3000' on departure. My FO essentially became single pilot as I couldn't discern the ASI properly and would've retracted the flaps too early if he hadn't stopped me.

The second at 36000' somewhere over Greece.

Both at night.
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Old 17th Feb 2016, 11:43
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Whatever hit you and caused you visual problems at 36000' was not a [email protected] pointer held by a chav, believe me.
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Old 17th Feb 2016, 11:48
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It definitely behaved like a handheld [email protected]

I didn't really care who was holding it at the time though.
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