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Citation2
27th Jul 2011, 16:27
Is it possible to keep one pack on during engine start ?

FCOM says : "Engine start sequence : If the crossbleed valve is closed , the valve located on the Starting engine side immediately closes when the Mode selector is set to IGN

It remains closed on the starting engine side ( provided the crossbleed valve is closed)"

Then further down there is a note : "If the crossbleed valve is open at engine start, both pack flow control valves close."

Crossbleed valves automatically opens with APU bleed ON . Does that mean that If the crossbleed valve is manually shut prior to engine start , only the associated pack will close ?

But then the question , can you start engines with Xbleed closed ?

Beeline
27th Jul 2011, 17:57
With your crossbleed closed with the plumbing you would only be able to start the left engine from the apu, BMC will cmd left pack valve to close on start.

No air would be on the right pack valve so it will be shut anyway. Pneumatically operated, electrically controlled.

The aircraft will not allow MES with ECS, not enough flow from apu, risk of abnormal start.

DutchOne
27th Jul 2011, 19:20
It might be possible if you start engines with the apu ---> you start ENG 2 first (not what airbus recommends) ---> close the crossbleed (as apu bleed has priority) ---> cycle the start selector, (now only ENG1 pack valve and bleed valve are closed) ---> start ENG 1 with APU, provide pack 2 with ENG 2

But why would you?

Citation2
27th Jul 2011, 22:53
Thanks for your inputs . I was just wondering whether it is possible because the FCOM notes say: If the Xbleed valve is closed the valve located on the starting engine side immediately closes " . So I don t understand why they are stating this case , if its not considered feasible or would give an abnormal start .

Then FCOM says : "If the crossbleed valve is open at engine start, both pack flow control valves close."

SO they are considering 2 cases : One where You would start with Xbleed closed which would result in the closure of only the associated pack .

Second case : Xbleed Open , and close both packs during start .

They put the accent on the Xbleed valve position during start, which give 2 different results . Please Refer to FCOM 1 Air Conditioning System , Packs

capt. solipsist
28th Jul 2011, 03:26
So I don t understand why they are stating this case , if its not considered feasible or would give an abnormal start .

Gallic logic :}

Last Ditch
28th Jul 2011, 13:03
Frankly, I see nothing wrong with the statements.
Its just making sure that the bleed air is provided only for engine crank during start.
Unless.... I am not seeing something you all are!!:ooh: