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In lots of commercial and defence aircrafts, bleed fault is annunciated because of mainly the following reasons:

  1. Overpressure/Overheat
  2. shut-off valve disagreement (i.e. failed open, failed closed)
  3. pressure regulator shut-off valve fails
  4. Precooler fails
  5. 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?

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    $\begingroup$ At the moment this question seems to be too broad and cannot be answered objectively. $\endgroup$
    – yankeekilo
    Sep 15 '14 at 10:13
  • $\begingroup$ @yankeekilo Thanks for your comments $\endgroup$
    – hagubear
    Sep 15 '14 at 18:08
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    $\begingroup$ Perhaps you can edit the question and add more information to make it more specifc (and easier to answer)? $\endgroup$
    – yankeekilo
    Sep 16 '14 at 6:29
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The question is quite broad but here's my understanding..

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?

No, since there is no fault (as you've listed). The bleeds are in the correct config and there is no disagreement between the valve and the switch. There is just no pressure to the system. You will get a 'Bleed Off' indication if your switch is on with no pressure to the valve(type dependant). Also you will get a pack off indication - if you've got the bleeds set to feed the packs.

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?

As I said above you wont get faults, but you may get indications that the bleeds are off.

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