Cap'n Crunch: "Yeah I know. You're probably right. But what's really stumping me, is: Can't a spiraling bus transmit a cabin decent (descent?) ADVISORY out on ACARS through HF? I mean ACARs doesn't know it's in deep doodo. Power should have been good. HF should have been good down to break up (VS fin loss) or dual flame out. Right?"
FWIW, The ACARS MU, Management Unit, is powered by 115 vac. I don't know which electrical bus on the A330, but it wouldn't be high priority.
I came to understand from prior posts that the ACARS was transmitting via the Satcom, and not HF. It would be tough for a spiraling plane to keep lock on a satellite, whereas the HF wouldn't much care. Why have both capabilities? Message cost on HF is lower.
GB