Re: Aircraft and lightning

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 12:24 PM 8/4/2005, you wrote:

> Some investigators speculate the cause of the crash
> was the lightning since heavy thunderstorm was going
> on in the area.
>
> Lightning or not,I'd like to raise few points
> regarding that matter.
> First of all,how lightning initiated by aircraft can
> be the cause of potentialy fatal accidents like
> that?Having in mind that commercial aircrafts are
> designed to be "lightningproof" and rigorous test
> standards for commercial aircraft and aviation
> equipment generally:
>
> http://www.sae.org

Lightning is associated with thunderstorms, which have all sorts of 
hazards that are not lightning related.

Relatively few aircraft accidents have been attributed to lightning 
(as you say, they're pretty lightning proof) and most commercial 
aircraft have been hit by lightning more than once.  (I've been in a 
airliner when it was hit, and unless you happened to be looking 
outside, I doubt anyone would have noticed) Accidents occur when 
something like a radome gets destroyed and that causes some further 
structural problem.

However, lots of aircraft crashes have occurred as the result of 
things like downbursts or wind shear events occuring in connection 
with a thunderstorm.

> Perhaps,situations in reality are way too complicated
> to be imitated by  voltage pulse generators tests-and
> that can sometimes lead to different outcome of the
> process?
> Inspite of huge action integrals ,or specific
> energies, (like 3MJ/ohm) and peak  currents  of 200 kA
> in aircraft test standards,seems that danger is still
> underestimated.How?

I don't think the danger is underestimated.  I think that the planes 
are lightning proof.



> Lightning is a multicomponent transient,especially the
> one ignited by a conducting object not attached to the
> Earth.Bidirectional/bipolar leader phase development
> could change triggered lightning pulses  having other
> (unexpected) consequences.
> IIRC,URL to videoframes of a lightning  strike to
> Boeing during take off from an airport in Japan have
> been posted before to TCML,clearly showing upward and
> downward branched leader structures lounched by the
> plane.
> That plane survived the lightning event without damage
> ,as well as Apollo 12 spacecraft in 1969. did too.
> But Boeing 747 struck in 1975 near JFK airport (NY)
> and Lockheed jumbo jet near Dallas in 1985. did
> not.Hundreds of passangers got killed.

Both the 1975 Eastern Flt 66 incident at JFK and the 1985 incident in 
Dallas were thunderstorm related but not lightning.

http://www-frd.fsl.noaa.gov/mab/microburst/micro_course.html
http://quest.arc.nasa.gov/people/journals/aero/coppenbarger/micro.html



> According to eyewitnesses ,they have strange
> properties of being very bright (almost blinding) and
> they produce explosive booms sometimes accompanied by
> sounds reminding of artllery salvos.

The one I observed was essentially silent (or, at least, you couldn't 
hear it over the relatively high background noise in the plane). 
There was a lot of turbulence at the time, so there was a lot of 
rattling and creaking noises, as well as a higher than usual amount 
of engine noise (no fool, that pilot.. carry lots of power, so you 
don't have to wait for the engines to spool up when you need it) It 
was VERY bright, but, inasmuch as there was lots of lighting in the 
area, most people had their window shades down and were trying to 
watch the movie.  (Aside from the inevitable folks going "we're going 
to die" from the turbulence.)

It struck near the end of the wing.  I have no idea if the stroke 
exited somewhere else.


As far as the sound of lightning "up close and personal" goes, the 
three times I've been near a stroke, it's sounded more like a very 
loud crack rather than a boom.  More precisely, it sounds like "hiss, 
buzz, crackle, BANG" as the field comes up before hand.  I'm not sure 
what the buzz comes from, but it's been there all three times, and 
it's very distinct from the usual corona hiss and crackle we're all 
familiar with.  Someone suggested that it's some sort of relaxation 
oscillation as a metal object in the field charges up and discharges 
with a streamer.  The whole time sequence is maybe 3 or 4 seconds. 
Except for the hiss and buzz, which can last a lot longer, and occur 
whenever the field is high, even without a long stroke, and is really 
really creepy, because you just know something big might happen.  You 
also get to feel your hair standing on end.