> > After getting a whack on the wing tip by lightning it sure
> > has changed my opinion about mechanical devices.
> Paul, Jos, Fred
> What about a Faraday cage round the avionics?
>
> Graham
Lightning goes where it wishes to go. In the case of Paul's
ILS/marker box, the thing was switched off, but his bolt traveled
along night lighting circuitry, arriving at the box via that wire.
The worst of four destructive events inside was a welding arc which
briefly struck, and part of an RF-grounding, steel card-edge guide
vaporized. No sensitive CMOS component was damaged; but even passive
components got whacked. Why it saw the case as a ground, I don't
know, and probably was just a side path of the electricity terminating
inside the box. Whatever it wants a ground to be? I recall some
document, FAA or other, concerning avionics systems in transport
aircraft, but it presumes a metal airplane as the preferential path.
However, there is a resulting, large electrostatic event within the
metal airframe, and that's where them ferrites and clamping diodes
come in. But I've never seen a general aviation box with that stuff,
nor might they accomplish anything in a plastic airplane.
Reg,
Fred F.
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