LH3431 B737 lightning strike?

[Starbear]

Bepopp

In what way is:

there is no way to prevent damage caused by a direct strike of lightning on anything.
etc

not erroneous or alarmist?

I repeat that there is protection and of course certification uses simulated lightning but it is nonetheless very intensive testing.

My point is quite simply that there is protection and I also added it is not perfect and yes it is vital to stay away from lightning but you can never guarantee to be clear even when avoiding the apparent sources.

You actually give a fair assesment but also alternate between the no protection argument but then say how often aircraft are struck with very minor results. The link to the accident a/c mentions it was struck by lightning just before landing; did the accident report actually blame that as the cause?

I speak from at least a point of interest if not apparent knowedge as I also am a LAME (and a pilot) and have been struck by lightning on more than one occasion (twice on one occasion, in an arrival holding pattern with very limited scope to avoid on that day) and yes it can be very frightening.

I have seen and am aware of some very significant damage occurring to a whole range of aircraft types, so I am certainly not suggesting that pilots can ignore lightning generating clouds simply because the aircraft is protected but it is wrong to say thay have no protection. Indeed many of the clouds producing lightning are the same as those that will produce significant turbulence (though not always) and pilots do or should strive very hard indeed to avoid those anyway.

[BEagle]

Lightning is not always predictable!

I was instructing a student pilot (he was in the LHS) in a VC10. In that aircraft the ancient weather radar is down by the LHS pilot's left knee and there is another display at the navigator's (yes, really!) station.

CBs had been predicted, but the weather radar showed only a few small returns about 15 miles away at 45 deg left.

Then we entered cloud in the descent - it had an unusual colouration and something made me suspicious. "Anything on the weather radar, nav?", I asked. "Nope"..... BANG!!

Lightning hit the AAR probe about a foot in front of the root end. The exit hole was later found on the radome; when the radome was removed, it had severe delamination.

So don't necessarily assume that the pilots took any 'risk' taking off in such conditions; more modern weather radars are vastly better than the orange porridge I used to work with - but when Big G decides to point the electric finger at you, it can come from seemingly nowhere!

[Collmac]

Are there any structures experts out there that would like to comment on our perception of the effect, rather than the cause, of this incident.

As we said before, the effect was severe vibration which caused the cabin sides to move in and out approx. 10-12mm (incidentally, I have moderated this from what I was saying when I first got off the aircraft to allow for the fear factor). I would guess the vibration frequency to be between 20Hz and 40Hz.

If we assume the cause to be flutter in the trim tab causing a vertical oscillating load at the horizontal stabiliser my interpretation of what we experienced is that the fuselage was actually ovalising where we sat in the overwing position. If this is the case would it be right to assume those to the front and rear of us experienced greater vibration, particularly vertically, than we did.

If this is the case my sypathies are with them.

[lomapaseo]

Are there any structures experts out there that would like to comment on our perception of the effect, rather than the cause, of this incident.

As we said before, the effect was severe vibration which caused the cabin sides to move in and out approx. 10-12mm (incidentally, I have moderated this from what I was saying when I first got off the aircraft to allow for the fear factor). I would guess the vibration frequency to be between 20Hz and 40Hz.

Some limited comments not necessarily conclusions about this event.

What the passenger sees and feels are vibratory modes in the soft non-structural cabin structures (between the cabin interior and the outside pressure vessel walls. This includes the interior window pane shields, as well as seat backs and tray tables. I had spent some time analyzing passenger videos of visible oscillations of interior fittings in somewhat similar events (to the passenger). The worst that I have seen is that the pretty looking panels in the loo fell off their attachments and made it difficult to open the door and take a pee

The aircraft structure (that holds the plane together) is quite resilient to forced vibration modes mostly due to dampening of the vibratory stresses across attachment points or joints not visible to the passenger. One might even see large amplitude oscilations in a surface albeit at low stresses.

The concern is always for an undamped oscillation like flutter outside the normal operating speed range. Also I would have some level of concern if the pilot was concerned that he could not control the level of felt vibration by controlling airspeed.

[VortexGen300]

Lightning protection - Alarmist?

Dear Starbear and others

Fortunately everyone is afforded the opportunity to express their opinion.

Please call me an alarmist - but please explain how bonding can "prevent" several thousand megavolt from damaging the intricate electronics of modern aircraft?

I have experience in the field of trying to protect electronic equipment from electrical surge such as lightning and other transient voltages.

Let me re-state : "Bonding (and earthing on the ground) does help to limit damage but the idea that it will protect? - I think that opinion is as alarming as my opinion as it might lead to people thinking they don't need to be as vigilant."

There is just too much we still have to learn - while a lot has been learned over the past century - we are still only seeing the tip of a humongous ice-berg floating accros the northern sea waiting to cripple and sink another Titanic.

So sorry for being an alarmist - but I'd rather be safe than sorry - and have to explain to investigators why something has occurred?

Greetings
VG300

[Starbear]

Ok Vortex you asked:

but please explain how bonding can "prevent" several thousand megavolt from damaging the intricate electronics of modern aircraft?

So I will have a go but this is definitely my last input because it seems pointless now. My original post was intended to give some comfort to passengers that even lightning strikes have been considered by the manufacturers and authorities AND pilots. You seem determined to suggest that an aeroplane cannot cope with a lightning strike at all. No, I know you didn't actually say that.

Here is the kicker, I suspect that you are probably a whole lot more knowledgeable than me on this topic but what I have said is correct. Aircraft are protected from the effects of lightning strikes but nothing is foolproof.

Here goes:

Bonding prevents damaging those intricate electronics by, providing a least resistance path for that megavolt strike to pass through the structure and exit to atmosphere And this CLEARLY works otherwise we would have numerous cases of serious damage to said electronics and the facts are that we don't (nope, don't have stats but any number of thousands of strikes versus examples of serious damage). Yes now and again there is rogue example of significant damage to tertiary structure and even primary flying controls such as an elevator (probably a result of poor or failed bonding) I am very aware of a very serious one in my own company.

And finally:
Nowhere has anyone and certainly not me suggested that:

"........ I think that opinion is as alarming as my opinion as it might lead to people thinking they don't need to be as vigilant."

out.

[cockney steve]

protection is inherent?

Not an A/c engineer, nor an Electronics one, but surely ,the big tin bird is fundamentally a jocking-great flying Faraday Cage....as such the charge will dissipate over the skin and leave the electronics untouched......I've never heard about queues of pax claiming a replacement for their frazzled watches, cellphones,i-pods and laptops....therefore I've a hunch that the A/c's heavily RF-shielded systems are extremely low vulnerability.

the flight concerned would appear to confirm.

I don't know enough about Plasma-balls (except you can make them in a microwave ,using half a grape ) but suspect that they don't present much threat , electronically....I wouldn't want to get in the way of one though!

[llondel]

The electronics attached to a properly-installed radio or TV mast is capable of withstanding a direct lightning strike, and the tower itself usually survives, albeit with an entry hole if there's a radome involved. So, correct bonding and proper electronics design and installation is going to keep most things working. The greatest danger on an aircraft is that the bonding along the preferred path proves inadequate and there's associated structural damage where the heating effect of the lightning has had an impact. The LH 737 demonstrated this by the damage to the parts at the rear where it was torn apart. The effect can be compounded if there's water in the path, given that the water will be turned to steam fairly quickly and so expand.

NASA did a whole series of tests deliberately flying aircraft into storm clouds to encourage lightning strikes so they could determine the effects. You get to see the benefits of that research today.

[RobboJon]

Lightning and composites

Interesting examination of what lightning will do to a composite aircraft in this AAIB investigation http://www.aaib.dft.gov.uk/cms_resou...pdf_500699.pdf of a lightning strike to a ASK-21 Glider from Dunstable. Interesting to note that a new CFI had reinforced the wearing of parachutes shortly before this incident.

Own experiences (both as SLF) include a strike in falling snow on final into Boston (Logan) in a BA 777. I was sitting in front of the wing next to the window and saw the reflection of the bolt striking the nose in the engine cowl. Apart from a loud popping noise, no other effect and a pleasant and informative explanation from the flight deck after landing.

By contrast, on an earlier flight departing the same airport in a fairly ancient BA 747 on a hot and hazy day at (I am guessing) 3-5,000ft a loud bang and a lurch to starboard (I wondered if an engine or the end of the starboard wing had departed) followed by about 15 seconds vibration and (apparently) laboured efforts to regain the climb. As I was seated in the middle of the cabin, I couldn't see what was going on at all. No announcements from the flight deck and - when pressed - the flight attendant informed me that the event had been caused by the air conditioning (at which point I decided he would not be my advisor of choice if any full blown emergency developed - or even if I wanted another gin & tonic). We flew to London with no explanation and there was considerable anxiety among the passengers - to the extent that on arrival at LHR the previously unknown to me lady on one side grasped my arm and said "made it". Seven hours or so of totally unnecessary tension that could have been resolved with a 10 second announcement. BA's attitude to its source of revenue did not endear the company to me that day!

My own inclination now is not to worry too much about lightning while traveling in the big silver birds - they seem robust enough to take most that is typically thrown at them (it's low on the list of potentially fatal risks compared with other - human and natural - ways of meeting your maker). Even the extreme LH experience that started this thread had a happy outcome, apart from an apparent disregard of the psychological well-being of its passengers that was reminiscent of my first BA lightning srike experience.

While flying around in the smaller stuff, steer well clear seems the only sensible maxim.

[BeeBopp]

RobboJon,

Thanks for posting the AAIB link on the Dunstable accident, very informative. Although the glider had no lightning protection and was destroyed the report interestingly determined by test and calculation that the lightning bolt was of a magnitude 8 to 9 times the level that which commercial aircraft and helicopters are built and tested to withstand. The 1995 Super Puma accident involved lightning intensity 3 times the certification standard. This is exactly what I was referring to when I previously mentioned rogue lightning bolts. I am not out to be alarmist but I frequently hear people discussing lightning strikes & going on about stringent certification standards, faraday cage blah, blah, etc. It is not that simple as the reports explains in great detail.

[PickyPerkins]

Photo of the damage

Photo of the damage here:
http://www.flightglobal.com/articles...ng-strike.html

[Basil Seal]

BeeBopp,

Without having even Googled it to find out but asking nonetheless, was there not an Iranian 747 on approach into Madrid quite a few years ago that came to grief and a lightning strike was suspected?

Unfortunately I cannot remember any of the details or even how a "routine" strike would have led to a loss of the airframe, but something about this makes me wonder. Did it even happen? Was it in Madrid? Was it Iran Air that was involved?

[lomapaseo]

Without having even Googled it to find out but asking nonetheless, was there not an Iranian 747 on approach into Madrid quite a few years ago that came to grief and a lightning strike was suspected?

Unfortunately I cannot remember any of the details or even how a "routine" strike would have led to a loss of the airframe, but something about this makes me wonder. Did it even happen? Was it in Madrid? Was it Iran Air that was involved

I believe that it was the TWA800 sister ship in the production line.

Operated by the Iranian AF

believed to have ignited the fuel in the wing due to poor static wicking. I suspect that IGH will produce a cut and paste of all the pertinent details when he discovers this post

[doncas]

Results of lightning strikes

I have extensive experience with lightning strikes on aircraft and I can safely say that lightning strikes on aircraft are very common. Lightning damage can vary from very mild (no damage) to very severe (as we have seen). Lightning strikes are so common in fact that there are entire chapters in aircraft Structural Repair Manuals to deal with each incident.
Typical lightning strike damage looks like a small burn mark or crater on the aircraft skin or on a rivet.

There are obviously limits to the size and dimension of the damage that is outlined in the SRM and these are strictly adhered to when inspecting an aircraft for lightning strikes. If there is a scorch, this material is generally blended out, inspected for cracks and then reprotected. If there is a crater, the damage is drilled out and a fastener is installed as a permanent repair. Very often one can see the extremities of an aircraft such as wingtips / winglets, trailing edges, static wicks and any other 'sharp' point of the aircraft most affected by 'exit points'. Protection from these exit points usually come in the form of the aforementioned static wicks. They are made of a high reistance material >10 MOhms. This allows for a gentle 'leaking' of static electricity from the aircraft and lightning strikes. In unusually high energy bursts of lightning these can be effectively blown off.

Getting around to our subject aircraft... The area that was blown off is a composite structure. It has no static wicks on it as they are fitted more outboard. It is possible that this lightning bolt was particularly powerful. This would have caused such a surge of electricity to pass through the composite structure that it heats rapidly and is liberated, as you can see.

Hope this answers some general questions, however if anyone has specific questions, please feel free to ask away and I'll help as much as possible.

[Basil Seal]

Thanks Lomapaseo, I am relieved to know that I was not imagining things! I think there was another 747 that crashed going into Madrid on a non-precision approach a number of years ago and I wanted to make sure that I was not confusing the two.

Doncas,

Something that I should know, but have alway been perplexed about, how great is the difference in damage susceptibility between the aircraft in the air (non-grounded) and being on terra firma such as in having the back stairs of the 727 touching the ramp (e.g., not just on the ground on the rubber tyres but an actual touch point). Have there been reports of severe aircraft damage from strikes whilst on the ramp? In my years I have not heard of any, but since you repair them you may well know.

[cjam]

Info for Steelfo, not sure if it is relevant but it sounds like the more info you're getting the better you feel about flying.
I fly the 737-300.
Pilots do practice different scenarios in simulators.
At my airline we have two four hour simulator sessions each six months. Two months ago I did one that focused on flight control problems. We departed and at about 10,000feet the airlerons jammed. The ailerons are a very important flight control that roll the aircraft in order to turn. We could control the aircraft through limited use of the spoilers and mainly by using rudder and landed with no problem. Then we did another flight where the horizontal stabilzer jammed, this makes it a bit tricky to make the nose go up and down but like the ailerons, there are built in systems that allow us to control the aircraft and get it back on the ground, albeit with a bit of sweat on the brow.
One thing that happens in situations like this is that you become quite busy re-organising the flight deck ,and the instruments, and your own brain (which checklists have been done? which need doing? what have we forgotten?)for a completely new plan with new problems and things to consider. In both these cases we made PA's to the passengers but these cases were not the same as your situation. For a start we were in a simulator, and secondly we had no major vibrations. My opinion is that.... If the pilots didn't know what sort of damage they had, and suspected severe structural damage as indicated by the vibration, they may have concluded (and fair enough too) that there was a real possibility of structural damage and further control difficulties and that landing the aircraft as soon as possible was the highest priority. That being the case they may well have been completely occupied with the tasks of flying the aircraft back to the field for landing. I wasn't there and don't know how much time elapsed but I can imagine this happening.
If that was the case then it is unfortunate for the passengers not to get the info they craved at the time but it is neccessary to prioritise your attention to what is most important when doing the job of flying.
Many pilots use a saying to remind themselves of the order of things, the saying is "aviate, navigate, communicate" as you can see, communicate comes third on the list of things to do and will only get done after both the aviating (flying the aircraft)and the navigating (are we clear of the ground ? heading to the right runway?) have been completed. And even then, communicating with the passengers is secondary to communicating with air traffic control and the cabin crew.
I hope this helps you feel better about the flight, there is every possibility that the crew did a fantastic job under the circumstances and that focusing on flying the aircraft to the landing was the most responsible and professional thing to do.
Cheers, cjam

[DC2 slf]

Lightning

<quote><snip>
Anyway if I could reassure Steelfo by stating that every commercial aircraft flying has or will be struck by lightning at some point. It is very rare for that damage to be severe enough to loss of control or a crash. In fact I can think of only 1 case off the top of my head and this involved small commuter aircraft. <snip><close quote>

I believe that in the early days of the B707 a crash of a PAA flight in Maryland was blamed on a lightning strike.

[Robert Campbell]

Lightning and composite structures

In over 40 years of flying, I've been struck 4 times by lightning -- once in a Beech D-18 and 3 times in DC-3s.

The only problem I ran into was that the D-18 strike fried ALL of the electronics, and this was because the operator of this 1970s commuter airline decided to run all of the electrical circuits through one big 75 Amp fuse (well, why run a bunch of little fuses or breakers when one BIG mother will do?).

The 3 strikes to the DC-3s left nothing more than small entry and exit holes.

In the 1990s I was involved with a company that produced promotional videos for kitplane manufacturers. I shot the air to air video.

When we were working with Glasair in Arlington, Washington State, USA, I asked about lightening strikes and was told that a strike would cause a composite aircraft to explode, so they ran wires in the resin layers to conduct the current.

They were also experimenting with a wire mesh layer embedded into the composite to carry the charge through the structure more effectively.

I know that they were doing contract work for Boeing at the time and some of that work was lightning strike related.

[Pegasus77]

Steelfo:

Aerodynamic vibrations can seem very severe in the cabin, but as Lomopaseo stated, the aircraft is built to cope with them and is still very well able to fly. A small piece of the elevator missing, like in this case, causes no big problem(just look at the photo of the missile-hit Bagdad-DHL-aircraft; even they were able to land safely).
This amount of damage after a lightning strike is huge, but still relatively harmless; I've been struck with lightning (that is: the aircraft I flew in) a few times, sometimes nothing happend, once we found 2 small black burn spots.

I do however understand how you must have felt; it is too bad that there was no PA-announcement from the cockpit. A standardletter from the LH-PR-department does not make you feel better, that is for sure. My guess is that the cockpitcrew had to set priorities. Flying the aircraft with structural damage is a priority. I hope you're able to believe me and my fellow pilots here on this forum that the actual danger on this flight was very very low.

Don't worry about any flashbacks or other symptoms of stress; they're perfectly normal if you were in a situation of great fear. Relax, take your time to recover, and book your next holiday by air :-) !


One last remark for the spotters & people who always readily pull out/google the latest METAR from the time of any incident: get a real hobby. It is soooo non-interesting to know what registration this or that aircraft has (besides, a REALLY COOL airman would describe a 737-300 as B733 and not as a 737-3, it only shows you're not part of our little world). "FEW CB" is something one reads sooooo often, and has soooo little meaning. A lighting strike can also come from clouds which don't even yet count as CBs. And a CB is not automatically a raging thunderstorm that burns trees and houses down.

P77

[CityofFlight]

Pegasus

Well said....I was hoping to see a response like this from someone who can talk the talk--including that weather doesn's have to be ominous in order to produce lightning.

I hope this helps Steelfo and any other SLF's who may need some reassurance after reading this thread.

CoF