Lightening strike
 

Probably a silly question, but nevertheless... :rolleyes:

Going back a year or two, I was on a BA A320 (I think, was either that or an A319 or A321) from Oslo into LHR.

Just as we were coming down over London, I could see all the usual "sights" from my seat, there was a loud crack - loud enough to spook me a touch - which the pilot promptly, and very calming, explained away as being a lightening strike; something he declared to be both normal and nothing to worry about.

Can such events ever be more serious than just a strike being absorbed, presumably by an a/c's own conductors?

Again - sorry if it's a stupid question! :ok:

It's not a silly question at all. It's quite scary when it happens and difficult to understand why it is 'safe'.

The lightning isn't absorbed by the aircraft, rather the strike travels through the aircraft, entering at one point and leaving at another. The occupants are quite safe for the same reason they are safe if they are in a car when it is struck - they are sitting in a 'Faraday Cage', where all the charge is conducted through the structure around them (safe) and not through their bodies (not safe, which is why we don't stand in the middle of a wet field during a thunderstorm).

After a lightning strike on an aircraft, the entry and exit points of the strike can be found, and these are usually small charred holes in a wingtip or similar. These can be repaired in the same way they would if that structure had been damaged in any other way. Of more significance can be that the strike permanently magnetises the aircraft, and that this magnetism affects all the magnetic compasses on board. Certainly a mandatory action soon after a strike is to compass-swing the aircraft to take out the Deviation errors in the compasses. In extreme cases, it may be necessary to de-Gauss the airframe to get the magnetic compasses to work within limits.

Metal aircraft conduct lightning strikes through their wings and fuselages without problem, and lightning conductivity is engineered into composite structures, too. I did, however, see the results of one fatal accident due to a strike - to a wooden glider. In this case, the lightning travelled from wingtip to wingtip along the only metal to hand - the aileron cables. They vapourised, and aileron control was lost. Rest assured, commercial airliners are very safe.

(Additional note. I have an electrical engineer friend who sails his boat around the world. Ever aware of the benefits of a Faraday Cage, whenever a storm looms up at sea he puts his GPS in the boat's microwave oven! He doesn't turn the oven on, of course. :ok:)

Teddy,

It's not a foolish question at all. A great deal of time, effort, and money has been sunk into the subject of lightening strikes on aircraft. The studies have ranged on how to prevent it, to what causes it, to the best conductors, etc. Lightening most often leaves a small burn hole on the way in, and a small burn hole on the way out. Occasionally it's caused damage ranging from exploded fuel cells to burned out avionics or electrical components.

I've had two lightening strikes which grounded the airplane and required substantial repairs, but most incidents have been very minor. In the two cases that required repairs, the situation was unique in the type of aircraft and the failure to properly bond the various parts of the aircraft together. In both cases it was on Piaggio Avanti's, and it burned holes through control surfaces, the outside skin, propellers, blew holes in the radome, and caused burn marks on the control hinge attach points, etc. In each case, the aircraft had been repainted, but no provision had been made when reattaching items such as static wicks, to allow them to properly conduct.

Normally, an aircraft is electrically bonded, and for most aircraft (which are metal), the entire structure conducts with no ill effect on the occupants or components. In aircraft which have composite (plastic, fiberglass, or other combinations of structures which don't conduct electricity well, or act as insulators or resistors) construction, special provisions are made to transfer electrical charges. These include aluminum or other metalic wire mesh embedded in the fiberglass matrix, or "diverter strips" of metalic materials on the surface of or in the composite material.

I performed airborne atmospheric research, in which we intentionally flew into and penetrated thunderstorms. As one might expect, we did experience lightening strikes as a result, and for the most part, these were uneventful. The worst I experienced when doing that was a two inch hole burned through an elevator control surface, though aircraft have had flame-outs or even experienced on board fires in extremely rare circumstances.

For the most part, lightening strikes are non-events, and aren't something that should worry you.

A lightening strike is when a whitish coloured paintbrush falls on you. Doesn't do much damage and usually most of it bleeds off before it dries. Leaves evidence of it's hit with whitish brushstrokes. Often hits cows in fields, which is why they are black and with whitish patches. Lightning strikes are much the same, but a bit more destructive!

Rainboe...............
 

Rainboe - you, more than anyone, are the hero of PPRUNE.

Seeing your name next to a post usually indicates somekind of disgusted response, which I love. Seriously - it's fantastic.

However, given your swift decision to pick me up on my mistaken mis-spelling of said electrical strike, I can only return the favour and point out that "its" does not need an apostrophe as, technically, it's a singular noun much like his or hers. Not his' or hers'. Which is why I suppose I'm a teacher and you're a pilot.

Seriously though my friend, thanks for the input. Always much appreciated :ok:

<Pounces with pedantic zeal>


Lightening strike? No, no, no. It's one used to remove weight quickly. At a stroke, so to speak.