Originally Posted by
oldoberon
"With electrical power to the FCCs maintained, the unit that provides MCAS changes between flights"
I am assuming by flights you mean airborne not one continuous flight number with multiple stops I e multiple take off/landing. I believe a flight from A to B stopping at C,D and E keeps the same flight number right through all legs. To meet your conditions of continuous power, on landing either the engines are kept running, APU is started or ground power applied, so how does the system know when next flight starts, Is there a weight on switch on the UC, or does it monitor engine power/aircraft speed to determine next flight has started.. What happens if all power is turned off how does it know which FCC to use.next time.
Why would the system do this switch over? On landing crew report any defects to ground crew for rectification, you land a perfectly serviceable a/c but the not in use AoA sensor had developed a fault , you don't know that ( unless you have the red light upgrade), next crew takes off and oops they have problems because the now in use AoA is faulty, Confusion reigns cant be AoA problem none were reported or even more likely it is the same crew on a multi hop flight so they know it was working. I would expect that system to at least tell them which FCC/AoA was supplying power to controls.
It is quite common for all kinds of systems to switch like that between flights. Usually by weight on wheels. If power is lost, it simply starts with a predetermined default source. If you'd always be using the same input, you'd never notice if the other one went INOP. Suddenly the always used source goes unserviceable and the backup has been unserviceable for ages but was never used so not noticed. As long as this behavior is documented in the FCOM it is absolutely not an issue. And no one simply dismisses a possible source of problems just because the previous crew didn't have any issues.