Originally Posted by
Loose rivets 
Having just read the AV H article in the parallel thread, I posted on some of the issues, and implied the impossibility of average crews comprehending the BackUp switch circuitry after a quick read in. If the AV H's questioner's knowledge is correct, things are very, very different to the concept of two switches simply being in series.
.
I have no doubt that this is true, but it is also largely irrelevant from a procedural viewpoint. The pilots don’t need to be able to read a wiring diagram and tell you all the things that happens when they throw the cutout switches. They just need to know when they need to throw the cutout switches - as in the case of the runaway stab trim procedure.
I know, and I concede I've always been a 'know every nut and relay' kind of bloke. But this, if true, means the function of the BU switch is much more subtle than I'd realised.
My first reaction was of curiosity, wondering where that would take us. It seemed to imply only throwing the RH switch might be significant.
However, it'll be 03 Sparrows again before I get my head down - about par for the course since November. I'll look at the AV H's list and circuits again tomorrow as I usually have a photographic memory for systems, but these logic changes are leaving me in a fog. Don't like it. Hope it's not age related!!