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bill1970

Failure - 9th stage bleed air

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As I was browsing the failures on the CDU during my last flight I noticed that the 9th stage bleed air had failed.  Did the research online and I know I must have operated the throttles above idle with the APU supplying bleed air ("Dual Bleed"). So I know what I did wrong :) but there were no indications in the cockpit (that I could see).  Question for the community: How would this failure be picked up on a real aircraft?  Is this something that would be found during the normal check before each flight, during an overnight check, or something even longer?  Obviously I could just clear the failure before the next flight, but it would more interesting to see what develops from the failure. 

 

Thanks,

 

Bill Rowe

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I had exactly the same failure about a month ago. There is no indication on the cockpit fot this kind of failure. Acording to a cockpit member I asked there is a chance that crew finds out there is something wrong from bleed air flactuations, but the only definete way is by ground crew.

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Not exactly...

The engine bleed system bleeds air from 5th and 9th compressor stages.

Most of the engines uses 2 compressor stages to provide the bleed pressure.

The reason is in the air pressure in the compressor itself. More deep you go inside the compressor (stage by stage) more the pressure and temperature increases. By accelerating you increase also the pressure in each stage.

As the 5th stage is at a lower pressure than the 9th stage it cannot provide bleed air at a sufficient pressure when the engine is at idle or near idle. In those low rpm conditions the 9th stage is regulated and used to provide bleed air at the right pressure. When engine is above the minimum rpm necessary to provide the correct pressure to the bleeds, the 5th stage will supply air.

So, if you have a failure on the 9th stage valve you will have pressure fluctuation during thrust variation (for example during descent) you will be able to read this fluctuation on the gauge, and you can feel a difference in air conditioning air flow, except for that, there is no light for the 9th stage valve.

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