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Robert McDonald

Can I start both engines on Ground Air Cart ONLY?

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I tried that, but didn't work: duct pressure 0 on right side.


Marc ter Heide

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You guys are all correct.  I can start one or the other engine with ground air cart (and YES, I even turned off Ground Air Conditioning for testing).  However the 2nd engine does not have enough duct pressure to turn over and start (I cannot reach 25 on N2).  I -must- turn on the APU to start engine 2.


 R. Scott McDonald  B738/L   Information is anecdotal only-without guarantee & user assumes all risks of use thereof.                                               

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I -must- turn on the APU to start engine 2

 

OR advance the throttle on engine one with the isolation valve open until you have the required duct pressure of 30 as recommended by the FCOM. So you don't HAVE to use the APU. The thing we know for sure at this point is that the cart alone is not sufficient to start both engines. Whether or not that is realistic is still a question at this point.


John Sturm

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OR advance the throttle on engine one with the isolation valve open until you have the required duct pressure of 30 as recommended by the FCOM. So you don't HAVE to use the APU. The thing we know for sure at this point is that the cart alone is not sufficient to start both engines. Whether or not that is realistic is still a question at this point.

 

Yes, the Engine Crossbleed air start you mentioned in the FCOM works perfectly.  It makes sense because of the danger to ground crew when firing up Engine #2.  So I start engine 1 on ground cart, then put Engine 1 online to the electrical bus, then disconnect ground power, leave APU OFF, and move APU bleed switch to OFF and Isolation Valve Switch to AUTO.  Engine bleed air switches are ON, Pack Switches are OFF, and move thrust lever for engine 1 up until duct pressure indicates 30psi.  Then engage starter switch for engine #2.  When N2 goes above 25, raise the fuel cutoff lever for engine #2, and Bob's your uncle!  Thanks for this handy tip for those of us that don't want to fire up the APU just to start ONE engine.


 R. Scott McDonald  B738/L   Information is anecdotal only-without guarantee & user assumes all risks of use thereof.                                               

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Gotcha - that was going to be my next question.  Interested to hear what you hear from them.

They tested it and agreed there was a problem. It's been added to the list of things to look at for SP2.

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They tested it and agreed there was a problem. It's been added to the list of things to look at for SP2.

 

Good news - thanks for the update!


Kyle Rodgers

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To me it is a PMDG choice!

The external cart is commanded by ground personnel, pressure is delivered only when required.

That means that the cart will be disconnected after the engine is started as the engine will be able to start the other one in a safer way than having a cart, a tube, a technician near a running engine.

The system has a connection ort, a check valve allows air to enter no other valves (except for the main system valves controlled by the cockpit) are present. Pressure will be present in one or both sides if the cart is supplying pressure.

It is perfectly normal that the cart will start to supply air when pilot wants to start the engine. so, it will rise few seconds before starting, it will be disconnected after engine start switch returns to OFF.

PMDG coded it correctly, simulating a normal condition, air supplied for the first engine start up procedure, then the cart is removed as it is in real life.

The only way to make it more "real" is to add ground crew communication and let us manage the air cart by switching it on and off, or disconnect it.


Regards

Andrea Daviero

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PMDG coded it correctly, simulating a normal condition, air supplied for the first engine start up procedure, then the cart is removed as it is in real life.

 

Indeed thats how we have done it in our operation. Get the cart ready as we were closing up the departure. Put air into system just before marshaller signals for startup, and remove the cart as soon as number one is turning.

 

Then depending on stand location and airplane direction relative to the terminal and other obstacles, either a single engine taxi out or on-place crossbleed startup was done.

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PMDG coded it correctly, simulating a normal condition, air supplied for the first engine start up procedure, then the cart is removed as it is in real life.

Except PMDG didn't code it this way, its a bug. If they had intended it they would surely have removed the air cart completely. They've even agreed it's wrong. If you want to only start one engine, then crossbleed the other you can, by disconnecting ground air yourself. If you want to start both off the ground air, which is possible in reality, you can't at the moment.

 

It simply isn't right for the pressure to go to zero with the ground sir still connected.


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The ground cart supplies air only on request, this means that may be connected one hour before engine starting and it supplies air only for one minute, just for the starting. Now, if the ngx cart supplies air from the connection it is normal, this because the user does not have a control of the air supply but only for cart connection.

As you cannot disconnect the cart while is supplying air, at the end of the starting sequence it will turn the air off as it is in the real world.

Now, if it is a bug (and why it is? Because you cannot start 2 engines with the cart? I'm pretty sure you can't do also on the real one) it is a good bug.

If there is a "bug" is present when connecting the cart and the pressure will be avaiable. It must be avaiable only when requested. That is something I think pmdg made automatic, and this is a feature not a bug. ;)


Regards

Andrea Daviero

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As you cannot disconnect the cart while is supplying air, at the end of the starting sequence it will turn the air off as it is in the real world.

 

Not sure what carts you all have, but ours were pretty dumb:

-Turn on, let idle to warm up

-On signal from crew, step power up to start pressure

-On signal from crew, return power to idle, disconnect, and move cart

-After push, turn cart off (assuming the push was long enough to allow the cart enough time to cool properly)

 

As such, if you wanted to start both from the cart, you would just not signal the crew to step the power back down between starts.


Kyle Rodgers

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I can do the cross-bleed or the APU start, either one is fine.  It's not a biggie...


 R. Scott McDonald  B738/L   Information is anecdotal only-without guarantee & user assumes all risks of use thereof.                                               

RQbrZCm.jpg

KqRTzMZ.jpg

Click here for my YouTube channel

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Not sure what carts you all have, but ours were pretty dumb:

-Turn on, let idle to warm up

-On signal from crew, step power up to start pressure

-On signal from crew, return power to idle, disconnect, and move cart

-After push, turn cart off (assuming the push was long enough to allow the cart enough time to cool properly)

 

As such, if you wanted to start both from the cart, you would just not signal the crew to step the power back down between starts.

The main problem is:

It is UNSAFE and UNNECESSARY to start a second engine from the cart. I never seen one done in this way.

I Always seen a crossbleed start. Now, if we want to have the control of the cart and it's air supply we must ask pmdg to add that feature, allowing us to make a ground personnel comunication to connect, start (and warm up the cart), add power to supply air, then idle it, disconnect, and so on... To me the system is good enough as it is. No need to spend time for cart control, just the need of connecting it to the plane in the CDU.

Same as for the ground power cart wich is not only connected and ready to the plane when connected.


Regards

Andrea Daviero

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Is it possible for the APU to supply duct pressure in flight?

 

I only ask this because the other day I was flying over Edwards doing systems failures testing and decided to shut down both engines at FL300. After setting both fuel control levers to cutoff and returning the throttles to idle, I started the APU and selected it on bus for electrical power. I turned off anti ice, set isolation valve to open, turned off both engine bleeds, turned off both packs and set APU bleed on. There was 0 psi duct pressure with the APU running. I wasn't sure if this was due to my altitude so I continued down to 15,000 before I was forced to perform windmill starts on both engines due to still having 0 psi duct pressure. Am I setting bleed air wrong or missing something?


Ben Weaver

SWA8485

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