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787 Lightning strike issues v FAA

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787 Lightning strike issues v FAA

Old 5th Jan 2020, 21:37
  #41 (permalink)  
 
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25 years and 15.000 hours, I never had a strike. It depends of course where in the world your main playground is.
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Old 5th Jan 2020, 22:37
  #42 (permalink)  
 
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Originally Posted by turbidus View Post
From my experience, I have been banged at least once a year if not more....so once a year is very conservative, and I think it is more often. Boeing claiming WORST CASE STRIKE (WTF does that mean??) is once every 10 to 15 years??? That has NOT been my experience.
The once/year average for a commercial aircraft is a standard industry assumption. Obviously it depends where you fly and when, and how hard you try to avoid that type of weather. Lightning is a somewhat random event, and just like snowflakes, every lightning strike is different. Some are big, some are small (as defined by peak voltage, amperage, and time factor of the strike), and a small number are massive. Attachment points, while predictable, are also somewhat random which makes a difference in how they affect the aircraft. Most lightning strikes are pretty much non-events - no adverse effects or aircraft damage - but not all.
Although not talked about much, it's simply not possible to completely protect from adverse lightning effects. For example, there have been documented cases where the pressure/temperature shock from a direct attachment to the inlet caused the engine to surge and flameout (CFM56-3/737-3/4/500). There was also a case back in the late 1990s where a 757 took a massive strike to the nose - the induced electromagnetic effects were so strong around the flight deck that it incapacitated one pilot and affected the other pilot - although not enough to incapacitate - so they landed safely and the pilots both recovered fully from the affects. Hence the importance of avoidance whenever practical.
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Old 6th Jan 2020, 02:51
  #43 (permalink)  
 
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UltraFan Pure carbon fibre is a good conductor indeed, but as GordonR_Cape points out, this only works if the CF is bonded at a molecular level. CF in that state is also extremely brittle, which is why it usually has to be embedded in a polymer matrix. But then there's no guarantee the fibres are in sufficient electrical contact to conduct well. The other factor that's terrible for lightning strikes into a CF panel is its thermal dissipation properties are woeful. The impact site of a lightning strike gets very hot very quickly. If that site can't conduct heat away from the impact site, the spot damage is far worse than on a thermally permissive material such as aluminium. I suspect this latter aspect isn't helped greatly by a copper mesh in the skin, but the conductive aspects most certainly are.
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Old 6th Jan 2020, 03:02
  #44 (permalink)  
 
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Originally Posted by turbidus View Post
"According to statistics published by the Royal Canadian Air Force, a plane can be struck by lightning on average every 1,000 to 3,000 flight hours. For commercial aircraft, that’s equivalent to one strike per aircraft per year.

Although The Boeing Co. (Chicago, Ill.) has reported that the probability of a worst-case strike could be as infrequent as once every 10 to 15 years, aircraft designs must be able to withstand such a strike.

Boeing recently reported in its AERO magazine that an airplane flies farther than its own length in the time it takes a strike to begin and end. Therefore, the entry point will change as the charge reattaches to other locations aft of the initial point. This can result in multiple burn areas or other damage that could have a direct effect on a plane’s structural integrity, and indirect effects that include damage to radio equipment and avionics or other electrically operated mechanisms, such as fuel valves when electrical potential differences or magnetic effects cause transient voltage spikes. Further, fatal accidents have occurred when current has arced around metal fasteners and ignited fuel vapors."

From my experience, I have been banged at least once a year if not more....so once a year is very conservative, and I think it is more often. Boeing claiming WORST CASE STRIKE (WTF does that mean??) is once every 10 to 15 years??? That has NOT been my experience.

IF the 787 is designed for a once in 15 year strike, there may be some valid concerns...

https://www.compositesworld.com/arti...osite-aircraft
It sounds like you are misunderstanding what Boeing was saying. They meant that the average rate of maximum amplitude lightning strikes (probably defined a those strikes with a peak current level in the top 5% of the range of initial return stroke peak current levels (roughly 100 kiloamps and above) is about once every 15 years per aircraft. The rough once per year rate experience you cited for noticeable lightning attachments (which includes strikes with peak currents well below 100kA) is consistent with the threat model used by industry in certification. Boeing was saying they attempt to design for the highest peak current levels in the accepted industry threat model, even though such a severe strike is only expected once every 15 years on average per airplane.
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Old 6th Jan 2020, 03:43
  #45 (permalink)  
 
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Originally Posted by Dave Therhino View Post
It sounds like you are misunderstanding what Boeing was saying. They meant that the average rate of maximum amplitude lightning strikes (probably defined a those strikes with a peak current level in the top 5% of the range of initial return stroke peak current levels (roughly 100 kiloamps and above) is about once every 15 years per aircraft. The rough once per year rate experience you cited for noticeable lightning attachments (which includes strikes with peak currents well below 100kA) is consistent with the threat model used by industry in certification. Boeing was saying they attempt to design for the highest peak current levels in the accepted industry threat model, even though such a severe strike is only expected once every 15 years on average per airplane.
Dave, I don't think the 'once every 15 years' rate is per aircraft, I think it's for the entire fleet (wouldn't swear to it though - going back to the 'I know enough about Lightning/EMI to be dangerous). But really bad lightning strikes are quite rare.
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Old 6th Jan 2020, 04:28
  #46 (permalink)  
 
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Hi TD. I'm not positive, but I'm pretty sure that would be "once every fifteen years per aircraft," or about once every 50,000 flight hours, as opposed to once every 50,000,000 hours if it was once every fifteen years for a fleet of 1000 airplanes for strikes near 100kA and above. I could be wrong. I don't know that aspect of the industry data either, but I know someone who does. I'll ask him and report back.
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Old 6th Jan 2020, 09:23
  #47 (permalink)  
 
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Frequency of strikes

Had three that I remember that damaged the aircraft and a couple that just involved inspections.
Damage was to radome with a few scorch marks.
10,000 hours over 23 years flying for european legacy carriers.
Worst was on approach into Sophia and a couple were between Zrh and Gva.
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Old 6th Jan 2020, 13:59
  #48 (permalink)  
 
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I'm very surprised to hear Boeing do not have any copper mesh in CRP in the wing over a fuel tank or flammable fluid leakage zone. Just because it is zone 3 does not meant it can't have a swept (or even direct) lightning attachment. I would have to be a pretty thick panel not to get to ignition temperature (200deg C) on the underside from a 100kA strike. The regulators have even started to question established guidelines for metal skin thickness to provide lightning protection. The Lightning ARC report makes an interesting read.
https://www.faa.gov/regulations_poli...RC-8202009.pdf

For an example of what lightning can do, look at the KATO Do228 accident (LN-HTA) https://www.aibn.no/Aviation/Reports/2007-23-eng
The elevator control rod end was blown out (due to a faulty bonding lead) and rod joints in the cockpit were overheated by a strike to the elevator.
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Old 6th Jan 2020, 17:24
  #49 (permalink)  
 
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Quoting from the CompositesWorld web-site, the spray on protection could be the panacea for lightning protection, easy to apply and easy to repair:-

NIARís Kostogorova-Bellar and Paul Jonas, director of NIARís environmental test labs, are conducting a U.S. Air Force-sponsored study on direct and indirect lightning and EMI shielding protection schemes for composite structures. One promising system is a conductive paint from Conductive Composites, in which the company disperses its nickel Nanostrand material. Formulated to handle lightning strikes in Zones 1A and 2A, the paint reportedly offers what Kostogorova-Bellar calls ďsuperiorĒ performance when compared to baseline LSP protection, such as aluminum and copper expanded foils and woven wire materials, including phosphor bronze. The paint, which reportedly can be resprayed in the event of damage, is expected to be a good alternative to the other methods.
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Old 6th Jan 2020, 23:26
  #50 (permalink)  
 
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Maybe I just attract the wrong sorts!

Doesn't everyone have the problem with street lights going out when you walk past??

Wait..on a serious note...Boeing asked for the reduction in copper foil, before or after, they realised workers were grinding it off during assembly???

Last edited by turbidus; 7th Jan 2020 at 00:00.
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Old 7th Jan 2020, 00:11
  #51 (permalink)  
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Originally Posted by turbidus View Post
Maybe I just attract the wrong sorts!

Doesn't everyone have the problem with street lights going out when you walk past??

Wait..on a serious note...Boeing asked for the reduction in copper foil, before or after, they realised workers were grinding it off during assembly???
Think you are conflating 7 late 7 wing foil issues versus 737 MAX engine cover issues - both relating to lightning . .

has to do with Arcs and Sparks ..
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Old 7th Jan 2020, 06:04
  #52 (permalink)  
 
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Originally Posted by Dave Therhino View Post
Hi TD. I'm not positive, but I'm pretty sure that would be "once every fifteen years per aircraft," or about once every 50,000 flight hours, as opposed to once every 50,000,000 hours if it was once every fifteen years for a fleet of 1000 airplanes for strikes near 100kA and above. I could be wrong. I don't know that aspect of the industry data either, but I know someone who does. I'll ask him and report back.
My colleague confirmed the 200 kA peak current in the SAE model is based on the 95th percentile strike from data measured at multiple ground towers over several decades. Although the calculation is extremely crude, and probably off a bit, Boeing's ballpark once every 15 years for a maximum design level strike would be rate per airplane, not rate per fleet.

TD - Perhaps you were remembering estimates for the rate of maximum strike attachments to nacelles? Attachments to nacelles are only a few percent of the total attachments to the airplanes.
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Old 7th Jan 2020, 09:20
  #53 (permalink)  
 
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So nothing to worry about. The frequency of a catastrophic strike which can blow up your plane when it strikes a tricky spot, is only one in fifteen years.

In the meantime, a regular(?) strike still happens yearly on average, taking the aircraft out of business from several hours to a day for a conventional aircraft (73,74). On the A330 I believe it usually is more like a day already, wonder what it will be on the B787.
I am not a mechanic but I understand most of the time is needed to find the entry and exit spots and assess whether damage was present (usually not). This has to be done in daylight or in a hangar. Now if you have to start repairs as well, it will be a lengthy AOG.
And BTW, I guess have had around 10 strikes myself in 25+ years, the one in every 3000 hours works for me..
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Old 7th Jan 2020, 11:51
  #54 (permalink)  
 
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I think that I have had four or five strikes in 36,000 hours. I may in fact be a pussy after having been driven within 2 nm of an active tornado as a youth. Didn't much care for the bruises from the shoulder harness nor the yips, groans and screams heard over the noise of the T-56ís . My last strike was suffered in the hold at BETTY near Hong Kong a few years ago. About 7nm from the nearest wx rdr return. Right on the left windscreen wiper. Woke me from a sound slumber. That 330 took three days to repair and many beers to debrief. Big fan of aluminium, avoidance, and enhanced debriefing sessions.
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Old 7th Jan 2020, 13:10
  #55 (permalink)  
 
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Originally Posted by matkat View Post
Originally Posted by SLF3 View Post
Without wishing to start Boeing versus Airbus debate, does the A350 have the foil in the wings?
The question is only because, if the wing construction is broadly similar and EASA / Airbus require it, that is strong evidence that the FAA should have insisted.
Yes it does, it(The A350) has copper sandwiches embedded in the CRP wing.
Yet, Airbus also finds that it is very difficult to prove that lightning related ignition sources in fuel tanks are extremely improbable (< 1 x 10^-9).
Back in 2014, they requested from the FAA that the proof of extreme improbability is moved from ignition sources to fuel-tank vapour ignition.
This switch allows to factor the use of inerting gas in the probability calculation.


https://www.federalregister.gov/docu...k-structure-to

As this came after the B787 certification (August 2011), it may be that Boeing wanted to benefit from this change in probability calculation rules.
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Old 7th Jan 2020, 14:23
  #56 (permalink)  
 
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So is working nitrogen inserting MEL for the Bus? An earlier post suggested It isnít for the 787.....

again, Iím not interested in a Boeing versus airbus debate, just looking for regulatory consistency around composite wings and lightning strikes.
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Old 7th Jan 2020, 15:26
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Originally Posted by Luc Lion View Post
Yet, Airbus also finds that it is very difficult to prove that lightning related ignition sources in fuel tanks are extremely improbable (< 1 x 10^-9).
Back in 2014, they requested from the FAA that the proof of extreme improbability is mov
787 Lightning strike issues v FAAed from ignition sources to fuel-tank vapour ignition.
This switch allows to factor the use of inerting gas in the probability calculation.


https://www.federalregister.gov/docu...k-structure-to

As this came after the B787 certification (August 2011), it may be that Boeing wanted to benefit from this change in probability calculation rules.
The 787 special conditions contained the same allowance to use probability of flammability in the overall catastrophic explosion probability calculation. Both sets of special conditions were consistent with a 2009 policy memo released by the FAA.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/12350ae62d393b7a862575c300709ca3/$FILE/ANM-112-08-002.pdf

That memo was later superseded by this 2014 memo.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/3cfa83c3b327d06c86257d1700654329/$FILE/PS-ANM-25.981-02.pdf

Both memos have the same allowance for inclusion of flammability. Both were issued after public comment periods.
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Old 7th Jan 2020, 15:29
  #58 (permalink)  
 
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Originally Posted by SLF3 View Post
So is working nitrogen inserting MEL for the Bus? An earlier post suggested It isnít for the 787.....

again, Iím not interested in a Boeing versus airbus debate, just looking for regulatory consistency around composite wings and lightning strikes.
The 787 inerting system is allowed to be inoperative under the MEL. The effect of this allowance was required by the special conditions to be included in the numerical probability analysis.
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Old 8th Jan 2020, 01:08
  #59 (permalink)  
 
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After reading about the exclusion from the original 2011 design,of the copper foil below the carbon composite surface and the insulating sealant that capped the heads of the fasteners,I am less and less inclined to accept the merit of the MEL relief for nitrogen system inop!
Where does cost cutting in the face of good practice end!
​​​​​​​
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Old 9th Jan 2020, 22:24
  #60 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Short answer: The fibers in carbon composite are not continuous, but embedded in a non-conducting polymer matrix.
Short answer maybe - but highly misleading.

Carbon fibre reinforced composites utilised in primary airframe structures are generally of the prepreg tape or woven cloth type. Cylindrical-structures may also be filament wound. Characteristic of all these forms is that the reinforcing fibres are continuous. Fibres are usually bundled in tows and woven to form the dry cloth reinforcement.

Polymer matrices reinforced with discontinuous fibres are generally employed for secondary/tertiary structures where structural integrity is not the primary design requirement.
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