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NassAir
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Lightning Strike on 777

Sun Jun 27, 2021 9:06 pm

Hello Guys,

Anyone can share with us what is the impact of a lightning strike on airplanes ? Just viewed this video and that was so impressive ! We can see a Boeing 777 of Air France having a lightning on final approach

https://www.youtube.com/watch?v=jg8oCZw3Uyc

Any inspections to be done ?

Thanks!
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Boeing757100
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Re: Lightning Strike on 777

Sun Jun 27, 2021 9:57 pm

Aircraft surprisingly get hit by lightning a lot!! Judging from that video, it hit the middle of the wing, so I don't know if there has to be any inspections or anything. But lightning strikes are usually not too serious, as the aircraft can withstand it and the cabin/cockpit is unaffected. Depends on where the strike is though...
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Starlionblue
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Re: Lightning Strike on 777

Mon Jun 28, 2021 12:03 am

If you're aware of the strike(s), you'd tell the engineer after parking. The aircraft exterior would then be checked for damage. Sometimes there are little holes. In many cases, speed tape is enough until a permanent repair can be performed. In other cases the radome might have cracked and needs to be replaced.

Lightning strikes are fairly common as Boeing757100 says. They can be very loud in the cabin.
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fr8mech
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Re: Lightning Strike on 777

Mon Jun 28, 2021 1:25 am

I’ve seen lightning strikes cause little to no damage, and I’ve seen them cause a lot of damage. Just depends on the circumstances. The components that we’ve replaced due to lightning damage are too numerous to detail, but flight controls and radomes are at the top of the list.

A reported lightning strike requires an inspection per the AMM.

If a mechanic finds damage during a routine walk around that can be reasonably considered lightning damage, an inspection is performed.
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PITingres
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Re: Lightning Strike on 777

Mon Jun 28, 2021 5:38 pm

I've been on a plane (BA 787) that had a wing lightning hit on final approach, just as the pilots started a go-around due to a sudden wind shift. I was looking right at it, too -- couldn't see a darn thing for several seconds afterwards. It didn't appear to have any significant effect, other than cabin lights being out for a short while. (Hard to estimate time, I'd guess under 30 seconds.)

The noise was oddly muffled, more like an intense poof than a bang. I wasn't even sure we were hit until an announcement from the cockpit confirmed it.
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889091
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Re: Lightning Strike on 777

Mon Jun 28, 2021 7:19 pm

NassAir wrote:
Hello Guys,

Anyone can share with us what is the impact of a lightning strike on airplanes ? Just viewed this video and that was so impressive ! We can see a Boeing 777 of Air France having a lightning on final approach

https://www.youtube.com/watch?v=jg8oCZw3Uyc

Any inspections to be done ?

Thanks!


Slightly OT, but is it just me or did the pilot grease that landing? I've turned the volume up as high as it would go, but can barely make out the MLG touching down.
 
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Starlionblue
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Re: Lightning Strike on 777

Tue Jun 29, 2021 12:30 am

889091 wrote:
NassAir wrote:
Hello Guys,

Anyone can share with us what is the impact of a lightning strike on airplanes ? Just viewed this video and that was so impressive ! We can see a Boeing 777 of Air France having a lightning on final approach

https://www.youtube.com/watch?v=jg8oCZw3Uyc

Any inspections to be done ?

Thanks!


Slightly OT, but is it just me or did the pilot grease that landing? I've turned the volume up as high as it would go, but can barely make out the MLG touching down.


Pretty smooth yes. :)
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zeke
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Re: Lightning Strike on 777

Tue Jun 29, 2021 9:40 am

NassAir wrote:
Hello Guys,

Anyone can share with us what is the impact of a lightning strike on airplanes ? Just viewed this video and that was so impressive ! We can see a Boeing 777 of Air France having a lightning on final approach

https://www.youtube.com/watch?v=jg8oCZw3Uyc

Any inspections to be done ?

Thanks!


I would think the pilots would have been totally unaware of this, and since they were unaware there would be no entry in the technical log. What would then follow is the standard post flight inspection by the ground mechanic and if was noticed they would make an entry in the technical log. The entry in the technical log by either the flight crew or the ground mechanic triggers an inspection process outlined in the maintenance manual.

It is possible for something like this not to be noticed as it can pass through without causing any damage. The aircraft departs again without an inspection. This is not dangerous as aircraft are designed knowing lightning does occur in nature, and the designers provide electrical paths for it to pass and dissipated.
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Horstroad
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Re: Lightning Strike on 777

Tue Jun 29, 2021 10:53 am

Boeing757100 wrote:
it hit the middle of the wing, so I don't know if there has to be any inspections or anything.

An inspection is always required. The damage has to be documented and assessed and repaired if required.

On the 777 the lightning strike inspection consists of two phases. Phase two can be deferred for up to 50FC

Phase 1 is a ground level general visual inspection of all areas where a lightning could strike. Any damage found has to be assessed and/or repaired per SRM. When all damages have been repaired or were found to be within limits or if no damage is found, the aircraft can be put back to service for a maximum of 50FC.

Phase 2 is a detailed inspection of all exterior areas requiring equipment to reach everywhere and perform NDI if required.

Usually there are multiple entry- and/or exit points. My personal best were 179 burn marks.
Lightning bolts like the pointy bits. Wing tips, stabilizer tips, static dischargers, aft edge of the engine nacelles. And they tend to "walk" along the fuselage, often jumping from one rivet to the next.

Most of the time the damage is minor. Just some burn marks that can be polished away and repainted. But especially on composite components the damage can be extensive. The plastic matrix doesn't handle heat quite as good as a metal structure. The area can be severely burnt and/or delaminated. But a powerful lightning bolt can just as well completely melt rivets. I've seen pictures of lightning strike damage, where the lightning bolt melted a hole in the fuselage large enough to stick a finger through.

Additionally to the structural damage, any damage to components has to be assessed. Usually the AMM requires to test the components and systems in the vicinity of the lightning strike. For example flight control system tests or in the case of this video a slat skew detection system test might be required. If the NAV light assy is damaged, an inspection of the wiring is required (internal wires of the light fixture, first 3ft of wiring from the damaged light in the direction of the circuit breaker, circuit breaker terminals and 1" of wires around the terminals).
 
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DocLightning
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Re: Lightning Strike on 777

Tue Jun 29, 2021 3:05 pm

Here's how I think about it:
Lightning, being electricity, is basically a huge blast of electrons. Now, the skin of a 777 is made of metal, and a feature of metals is that electrons can move quite freely within a volume of metal, which is why we use metallic cables to transmit electricity over thousands of miles.

So in a lightning strike, a whole bunch of extra electrons get introduced into the metallic skin of the airplane. Because electrons are all negatively charged, they "try" to get as far away from each other as possible, which means that they all tend towards the very outer layers of the airplane's skin. Eventually, the charge on the airplane gets big enough that the electrons leak back out into the atmosphere. So basically, the lightning bolt will travel around the very exterior of a metallic object like an airplane. In addition, airplanes are designed to have static discharge wicks (like the ones on the wingtip of the 777) that help to control where the electrons will exit so that they cause the minimum amount of damage to any overlying structures.

So what you saw here was the bolt strike the airplane and then the static discharge wicks on the wingtip released the electricity back overboard, which explains that brief glowing streak from the wingtip.

The newer CFRP aircraft actually have to have metallic nets embedded into their skins so as to conduct the lightning safely around the airframe.
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dfwjim1
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Re: Lightning Strike on 777

Tue Jun 29, 2021 9:24 pm

PITingres wrote:
I've been on a plane (BA 787) that had a wing lightning hit on final approach, just as the pilots started a go-around due to a sudden wind shift. I was looking right at it, too -- couldn't see a darn thing for several seconds afterwards. It didn't appear to have any significant effect, other than cabin lights being out for a short while. (Hard to estimate time, I'd guess under 30 seconds.)

The noise was oddly muffled, more like an intense poof than a bang. I wasn't even sure we were hit until an announcement from the cockpit confirmed it.


I was in my car stopped at a traffic light when a lightning bolt hit a power pole directly across the street from me. The flash was intense but the thunderclap wasn't loud at all, kind of surprising to me.
 
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fr8mech
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Re: Lightning Strike on 777

Wed Jun 30, 2021 3:40 am

DocLightning wrote:
Here's how I think about it:


Not a bad analysis.

Lightning strikes can cause all kinds of damage. There are at least 2 points of damage; the entry point and the exit point. More often than not, there will be additional damage between the 2 points as the lightning skips across the fuselage.

The exit point tends to exhibit more damage than entry points or the points along the path of the strike.

Usually, the entry point and the tracks along the fuselage are little divots in the metal and/or fasteners. If the lightning happens to skip across a fiberglass surface, the fasteners will usually be burned and will most likely require replacement.

The exit points will usually be along the trailing edges of the flight controls, though it seems to me, that the trailing edge of the translating sleeves on the B767 have an affinity for being damaged by lightning.

I've seen the trailing edges of ailerons and elevators blown apart. Rudder caps on the B747 seem to take a beating. Don't get me started on MD11 winglets.
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CALTECH
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Re: Lightning Strike on 777

Thu Jul 01, 2021 11:23 pm

DocLightning wrote:
In addition, airplanes are designed to have static discharge wicks (like the ones on the wingtip of the 777) that help to control where the electrons will exit so that they cause the minimum amount of damage to any overlying structures.

So what you saw here was the bolt strike the airplane and then the static discharge wicks on the wingtip released the electricity back overboard, which explains that brief glowing streak from the wingtip.

The newer CFRP aircraft actually have to have metallic nets embedded into their skins so as to conduct the lightning safely around the airframe.


Static wicks are not designed to do what you posted. They can have a lightning bolt go through them, but usually there is damage to the static wick. Many lightning bolts hit the fuselage and exit the fuselage. Many rivets usually melt and it looks like a woodpecker went down the fuselage.
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fr8mech
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Re: Lightning Strike on 777

Fri Jul 02, 2021 12:17 am

CALTECH wrote:
Many rivets usually melt and it looks like a woodpecker went down the fuselage.


I once called them "pecker tracks" on a conference call. I swear there was dead silence for 10 seconds. Later, I got a call from my boss and told me not to call them that anymore.
When seconds count, the police are minutes away, or may not come at all.
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extender
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Re: Lightning Strike on 777

Fri Jul 02, 2021 10:48 am

Static(wicks) dischargers provide a means of dissipating precipitation static accumulated on the airframe. They are referred to as wicks because they originally were flexible. See photo:

Image
 
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CALTECH
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Re: Lightning Strike on 777

Sun Jul 04, 2021 12:13 am

fr8mech wrote:
CALTECH wrote:
Many rivets usually melt and it looks like a woodpecker went down the fuselage.


I once called them "pecker tracks" on a conference call. I swear there was dead silence for 10 seconds. Later, I got a call from my boss and told me not to call them that anymore.


That's all I ever heard them referred to as. Never understood the offense taken when talking about woodpecker drumming.......
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AirKevin
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Re: Lightning Strike on 777

Sun Jul 04, 2021 2:55 am

CALTECH wrote:
fr8mech wrote:
CALTECH wrote:
Many rivets usually melt and it looks like a woodpecker went down the fuselage.

I once called them "pecker tracks" on a conference call. I swear there was dead silence for 10 seconds. Later, I got a call from my boss and told me not to call them that anymore.

That's all I ever heard them referred to as. Never understood the offense taken when talking about woodpecker drumming.......

I'm guessing whoever got offended wasn't exactly thinking of a woodpecker. I actually had to look up the term pecker to see what other meaning it could potentially have.
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CALTECH
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Re: Lightning Strike on 777

Sun Jul 11, 2021 2:24 am

AirKevin wrote:
CALTECH wrote:
fr8mech wrote:
I once called them "pecker tracks" on a conference call. I swear there was dead silence for 10 seconds. Later, I got a call from my boss and told me not to call them that anymore.

That's all I ever heard them referred to as. Never understood the offense taken when talking about woodpecker drumming.......

I'm guessing whoever got offended wasn't exactly thinking of a woodpecker. I actually had to look up the term pecker to see what other meaning it could potentially have.


Such dirty minds.....

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