Originally Posted by
freshgasflow
I am not an aviation professional so grateful if someone could explain things to me:
If the theory of lightning strike are true, how does it lead to electrical failure ? I thought that an aircraft aluminium or metal mesh composite effectively created an Faraday cage ?
If there were local electrical transients, would this only trip circuit breakers. which presumably could be reset quickly ?
Thank you.
Aluminum does a good job of conducting the lightning current, however there can be significant 'induced' current on internal wiring (similar to the way a transformer works - current through the external windings induce a current to the internal windings). However, this should be designed for per 25.1316:
§25.1316 Electrical and electronic system lightning protection.
(a) Each electrical and electronic system that performs a function, for which failure would prevent the continued safe flight and landing of the airplane, must be designed and installed so that—(1) The function is not adversely affected during and after the time the airplane is exposed to lightning; and(2) The system automatically recovers normal operation of that function in a timely manner after the airplane is exposed to lightning.(b) Each electrical and electronic system that performs a function, for which failure would reduce the capability of the airplane or the ability of the flightcrew to respond to an adverse operating condition, must be designed and installed so that the function recovers normal operation in a timely manner after the airplane is exposed to lightning.
(note, the quote is the FAR, however the regulation has been harmonized so the EASA CS version should be identical - and to export the Superjet they'd have to show compliance with the FAR/CS)
There is a lengthy Advisory Circular that provides specifics on how to show compliance.
In short, critical systems can not be significantly affected by the lightning transient, essential systems can be affected but must self recover (with no resetting of circuit breakers). The allowable recovery time depends on the system, but 10 seconds was a good rule of thumb.
So the short answer is that a lightning strike should NOT have resulted in widespread system failures.