Originally Posted by
tdracer
DeeVee - again, a couple decades since I was involved, but based on what I remember, the only way they could have lost all main bus electrical power (with both engines running) would have been either:
latent failures in the electrical bus isolation system (there are regular maintenance checks to confirm such failures are not present),
Would speculate that we getting in the right track ...
AC Power is the "standard", or is prefered, for several systems in commercial air transport aircraft. Don't ask me why, as I don't know the reason ...
AC Power has however a big inconvenience. You can have 10 sources of good working AC Power available. However only 1 of those sources can supply power to an AC Bus at a time. You cannot connect them in Parallel, or in Series, like with DC Power.
If a contactor becomes stuck, for whatever reason, and doesn't "let go", to allow another source of AC Power to power the an AC Bus that is without power, then this kind of scenario can happen. Several sources of AC Power available, but none is allowed to supply power to AC Buses that are without power, because the contactor is stuck in position that allows only the Failed source to power the Bus, or it didn't shift completely to allow another source in.
AC Power ... we owe that to Tesla