Originally Posted by mm43
Reference to the Cabin Pressure Controller schematic shows that in Automatic Mode the barometric reference comes from the ADIRUs, but my take is that should that reference fail, then it selects Manual and the Safety and Relief valves will attempt to keep Cabin Pressure equal to the outside when descending below 8000/7350 feet.
Good guess, but how would the controller know "outside" pressure without ADIRUs providing "oustide" pressure?
That's the bug and what might have caused this alert.
S~
Olivier