In lots of commercial and defence aircrafts, bleed fault is annunciated because of mainly the following reasons:
- shut-off valve disagreement (i.e. failed open, failed closed)
- pressure regulator shut-off valve fails
- Precooler fails
- Computer failure
However, when there is an emergency condition e.g. engines are lost/off/unavailable (i.e. no generators) and also no APU possible, should there be any bleed fault? Given that the aircrafts are only running on batteries, should there be a bleed fault because your sensors and computers aren't powered up completely?
I know that you have things like built-in autotest stuff that goes on before the computers are powered, but surely when the aircraft is on batteries/emergency power, should there be any bleed faults?