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kmanning

MD-11 APU

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Hi,

I want to make sure I'm correct about something here. After the engines are started up and stabilized, am I supposed to shut down the APU myself or does the environmental system shut it down? I always thought the system shuts it down automatically but when I checked the overhead panel, I noticed that the APU would still be running and I have to shut it down.

 

Ken.

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I think your confusion arises because of the following:

 

If APU is started from the main APU START/STOP switch, the APU can only be shutdown by pressing the same switch.

 

If however the APU is started by pressing the APU PWR switch on the electric control panel, AND after engine start you press the APU PWR switch to disconnect APU electrical power from the busses, the APU will shut down provided it is not supplying bleed air.

 

I expect you have used alternative methods to start the APU, and this has led to the confusion.


Peter Schluter

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Hi Peter,

Before engine start, what I do is press the APU PWR switch on the electric control panel. Then on the AIR panel, I press the APU button, which I assume is for the bleed air. After the engines are stabilized, I press the APU on the AIR panel. But I may be forgetting to go back to the electric panel and press the APU PWR switch. So, I need to remember to go the electrical panel and press the APU PWR switch, correct? By the way, am I pressing the correct switch on the AIR panel? I thought that's what the manual said.

 

Ken.

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I just checked this.  After engine start, the APU PWR switch is automatically switched off, as engines now provide power. if you now press the APU bleed switch to disconnect APU bleed air, the APU will turn off. This is not the same as I described above, which I got directly from the manual, so i am a bit confused now!

 

Having experimented I think the logic is:

if you start the APU with the APU PWR switch on the electric panel, then after engine start, the APU will shutdown automatically when it is no longer supplying any electric or bleed load.

If you start the APU with the APU START/STOP switch, you need to stop it by pressing theSTART/STOP button, irrespective of any load.

 

So it seems you do not need to press APU PWR switch after engine start, as it will auto disconnect. You do need to press the APU bleed switch however, to disconnect the bleed air.


Peter Schluter

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My MD11 teacher for the PMDG MD11 told me the way they use it in real life (He is a reallife MD11 pilot).

 

To start the APU they use the APU PWR switch (ELEC). The APU starts it self en will provide power.

 

After that they use the APU switch (AIR) to establish airco and bleed air.

 

After starting the engines you just press the APU (AIR) switch again and the APU will shut down. You know this by the flickering start/stop light at the manual APU part of your overhead!

 

I Hope this helps!

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Thanks Guys,

I remember a couple of times I did press the APU PWR switch after pressing the APU on the AIR panel. If I remember correctly, I think Ruud Bakaar stated that the APU is automatically switched off by the environmental system from the ITVV MD-11 video. So I must have been switching the APU back when I pressed it again. So, all I need to do is press the APU on the AIR panel. I'll try that and see what happens.

 

Ken.

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Well,

I've tried those suggestions and the APU is still not shutting down after I press the APU on the AIR panel. I start the APU by using the APU PWR switch on the electric panel. When the APU is available indication is shown on the IECAS, I press the APU on the AIR panel. Then I start the engines. After all engines are running, I press the APU on the AIR panel. But the APU continues to run and there is no blinking or flickering lights on the APU overhead panel. Something is not working right.

 

Ken.

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Check to see if this is happening. After you start the engines and shut off the air it will not flicker or blink and the APU available light does stay illuminated as it begins the cool down process. However, the APU Start/Stop switch on the Aft APU Overhead control panel should illuminate from ON to OFF I believe. If this is happening the APU should shut down automatically after a few minutes. 


Brandon Gaumond

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Check to see if this is happen. After you start the engines and shut of the air it will not flicker or blink and the APU available light does stay illuminated as it begins the cool down process. However, the APU Start/Stop switch on the Aft APU Overhead control panel should illuminate from ON to OFF I believe. If this is happening the APU should shut down automatically after a few minutes. 

 

This is how it works with my (FS9) version.


Peter Schluter

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Hi Peter,

Yes, when I press the APU on the AIR panel, the APU Available light does stay lit. The APU Start/Stop switch on the APU overhead panel does not go from ON to OFF. It just stays ON. Even after I taxi to the runway for take-off, which takes about 5 minutes if not more, the APU switch on the overhead panel still says ON.

 

Ken.

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Keep it simple. I never assume anything that is supposed to work automatically will work automatically.

 

I turn the APU on using the APU button on the APU Panel. Then I turn the APU air button on using the Air Panel. After engine start, I reverse the order.

 

At my age, if I don't follow the same routine, I always forget something. Also, use the warning lights and messages on the instrument panel. Scan the overhead panel to confirm there are no illuminated lights - anywhere!


Eric Parker

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