A320 Family - APU Usage
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A320 Family - APU Usage
Can I ask..
Are you permitted to depart with the APU running and bleed on under certain circumstances? If so, what could be the possible circumstances (if its a million and 1 answers, I only would like a brief explanation)?
Many thanks in advance..
Are you permitted to depart with the APU running and bleed on under certain circumstances? If so, what could be the possible circumstances (if its a million and 1 answers, I only would like a brief explanation)?
Many thanks in advance..
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Just to carify a bit, 'packs off' in this case means that the packs are actually on but driven by the APU bleed. This still gives you air conditioning, the engines have the benefit of not supplying bleed air to them and therefore EGT is less allowing for a degree of flex or better performance.
In the event of the APU failing during takeoff, the packs are still selected and the engines would immediately pick up the supply to them causing an increase in EGT.
In the event of the APU failing during takeoff, the packs are still selected and the engines would immediately pick up the supply to them causing an increase in EGT.
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Actually, Torque 2, what you said originally in your first paragraph is incorrect.
Packs Off means exactly that; the air conditioning packs are physically selected 'OFF' (as is the APU and/or APU Bleed).
What you describe is "Packs Supplied by APU Bleed"; i.e. the air conditioning packs are selected 'ON', and the APU/APU Bleed are also selected 'ON'. However, you are correct in what you say in your second paragraph with regard to a failure of the APU, should this method be employed.
As Dan says, either of these procedures can lower the required thrust, leading to reduced fuel flow, reduced temperatures, and increased engine life. In other words, big cost savings.
'FLEX' temperature is a way of 'tricking' the engine into thinking that the Outside Air Temperature is significantly warmer that the actual Outside Air Temperature, so that the engine will supply a reduced thrust setting.
This is achieved by inserting an artificially high temperature into the Performance Take Off Page in the Flight Management Computer of, typically, between 30°C and 60°C; the engine "thinks" that it is a very hot day, and supplies a reduced thrust setting that would avoid exceeding any of it's temperature limits were it really 30°C-60°C outside!
Packs Off means exactly that; the air conditioning packs are physically selected 'OFF' (as is the APU and/or APU Bleed).
What you describe is "Packs Supplied by APU Bleed"; i.e. the air conditioning packs are selected 'ON', and the APU/APU Bleed are also selected 'ON'. However, you are correct in what you say in your second paragraph with regard to a failure of the APU, should this method be employed.
As Dan says, either of these procedures can lower the required thrust, leading to reduced fuel flow, reduced temperatures, and increased engine life. In other words, big cost savings.
'FLEX' temperature is a way of 'tricking' the engine into thinking that the Outside Air Temperature is significantly warmer that the actual Outside Air Temperature, so that the engine will supply a reduced thrust setting.
This is achieved by inserting an artificially high temperature into the Performance Take Off Page in the Flight Management Computer of, typically, between 30°C and 60°C; the engine "thinks" that it is a very hot day, and supplies a reduced thrust setting that would avoid exceeding any of it's temperature limits were it really 30°C-60°C outside!
Last edited by fmgs; 9th Sep 2008 at 11:41.
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Thanks for the correction FMGS, I was referring to post 2 where the situation is referred to as 'packs off'. I know what the situation is on the airbus, the original poster may not but he is now fully aware.
