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BoFrost

Engine start with external Air Supply

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Hi Folk's, I have a problem starting the engines with ground air only. It is no problem to start up engine number 2. But when trying to start number 1, it will not success, because the air pressure only will come up to about 20 Psi, which is not enough.I tried several combinations with Isolation Valve in all positions. Only when I will put a little bit throttle on engine 2, the pressure will raise to about 30 Psi and it is possible to start number 1.I am still using the NGX in the RTM version, as I do not have any problems with this version.So is it a bug, or do I make something wrong ?Could some pleaase tell me how to start up with external Air ? Thanks

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It was already posted, maybe a bug but I must try to see what it's wrong. Basically is wrong to start te engine 2 with ASU.... The ASU is connected on te right side of the plane, and the engine running can be dangerous for personnnel and equipment.

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Ok, I tried...As I was supposing before, and noone replied to me with the info, the ASU goes to idle (so without supplying air) after the first engine start.The 20PSI you see is the pressure from the engine bleed.It is a correct procedure to cross start the engine, so ASU must be removed to do it.Bug? I think is a pmdg choice, it is not a good thing to start both from ASU. Maybe pmdg simulated the cart going in idle, that is a step needed before removing the ASU tube from the plane.Use cross engine start.

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Thank you so much ! I could not find it in the documents.I will try it later on. Great community !

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I found something in the QRH: 6 Crossbleed start:PACK switch (affected side) . . . . . . . OFFDUCT PRESSURE. . . . . . Minimum 30 PSIAdvance the thrust lever to increase duct pressure if needed.ENGINE START switch(affected engine). . . . . . . . . . . . . . .GRD So I was not to wrong, as I found out to give a little bit throttle to reach 30 PSI !

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Pack switch both OFF, wit both off more air is avaiable for engine start.
Since the checklist he posted said "PACK switch (affected side)", I assume it refers to an engine restart in flight, meaning that you need to have at least 1 pack on to ensure pressurization. But, yes, if you do this on the ground, definitely both packs off.

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I found something in the QRH: 6 Crossbleed start:PACK switch (affected side) . . . . . . . OFFDUCT PRESSURE. . . . . . Minimum 30 PSIAdvance the thrust lever to increase duct pressure if needed.ENGINE START switch(affected engine). . . . . . . . . . . . . . .GRD So I was not to wrong, as I found out to give a little bit throttle to reach 30 PSI !
Don't look in the QRH for this. As pointed out previously, it's in the Supplemental Procedures.

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Hi, I'd say starting engine No.1 with ASU would be preferred unless you'd like to give some hard moments for the ground crew... :) And advancing the throttle for No.1 to about 40% N1 (or to get 30 PSI) is another thing I'd try if I were you. Just 2 hints I thought are useful.RgdsGabor

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Packs - OffIsol.v. - ClosedEngine 2 S/W - GroundWhen engine 2 is up and running..Isol.v - OpenEngine 2 - spool up a lil bit (monitor psi.)When 30psi or above - Engine 1 S/W - Ground Ta-da!

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This is wrong and dangerous for ground personnel and equipments.The n1 engine must be started first.Packs OFFIsol. Valve AUTO or OPEN (in auto position, the packs off will command isolation valve to open)Inform ground crew to power up te ASU output and verify if pressure on the left duct is present and above 30PSIEngine 1 knob GNDAt the right N2 or maximum motoring speed start lever up.Wait for starter cutout. In this moment you will see that te pressure in the pneumatic duct will decrease to the engine bleed value (if bleed is on) or to 0, but the ASU is still connected.Remove ASUNow, with the conditions above, just add power to the left engine and look at duct pressure. When sufficient start the engine number 2 normally, whatch the pressure in the duct and N2 to see if it is spooling up correctly.

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You shouldn't have to use a crossbleed start technique for the second engine start if the ground air connection is still available. There is a logic error in the pneumatic model as it is at present. As soon as one engine is running the model seems to want to use it as a source of air in preference to the ground supply even if the engine bleed switch is closed (which should not be possible). After starting the first engine, duct pressure recovers to about 36 psi. If the second engine is selected to ground start the duct pressure drops to zero. If you don't attempt the second start and the bleed valve of the running engine is opened the pressure drops to 20 psi (typical of bleed from an engine at idle). If that bleed valve is closed again the pressure drops to zero. Now the only way to get duct pressure from the ground source back is to shut down the engine. From a pneumatic model design point of view, the highest available source pressure should supply the pneumatic duct. So if the ground source is putting out 36 psi, the engine pressure of 20 psi should make little or no difference. If the engine bleed valve is closed there is no engine bleed pressure connection to the duct. Kevin Hall

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I've checked your scenario wit starting the first engine with bleeds OFF. After maybe 2 seconds or 3 after te starter disengages the ASU pressure will be removed (so it's not linked to the second engine start).To me, as there is no error on the aircraft logic in this, (maybe we sould think about ASU logic now) it could be a choice.It is common use to start the second engine after pushback with cross engine start and limit te ASU start and usage times (ASU usage will cost more than fuel used for an engine).It is correct that to remove the ASU its pressure must be 0.But, if we want to start both engines wit ASU maybe we must have an option to do it. Something like cycle RMOVED-CONNECTED on the CDU.However, is not a bug, is a choice.PMDG can help us by explaining what they did.

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I've checked your scenario wit starting the first engine with bleeds OFF. After maybe 2 seconds or 3 after te starter disengages the ASU pressure will be removed (so it's not linked to the second engine start).To me, as there is no error on the aircraft logic in this, (maybe we sould think about ASU logic now) it could be a choice.It is common use to start the second engine after pushback with cross engine start and limit te ASU start and usage times (ASU usage will cost more than fuel used for an engine).It is correct that to remove the ASU its pressure must be 0.But, if we want to start both engines wit ASU maybe we must have an option to do it. Something like cycle RMOVED-CONNECTED on the CDU.However, is not a bug, is a choice.PMDG can help us by explaining what they did.
Once the running engine is producing bleed pressure the ASU pressure disappears. But the ASU hasn't been disconnected, as you assume, since if the engine is shutdown ASU pressure reappears. This is a simulator and as long as the ASU is selected it should supply pressure. If your airline's SOP is to start one engine using the ASU then you should disconnect the ASU after the first start. Why should users have to reconnect the ASU for the second engine start?It is a bug, but may not be an easy one to fix.Kevin Hall

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The pressure disappears after few seconds from starter cutout (that is almost the same time when engine bleed comes on if selected), but pressure is removed also if bleed is off.The ASU is an external cart and when it is connected to the airplane 3 conditions maybe possible:Cart connected but engine is stopped, so no air to the aircraftCart connected, engine in idle with no air suppliedCart connected, and air supplied to the tube tat connects to the aircraft.The cart is commanded by the ground crew. After the first engine start is probable that the ASU is moved to idle power. It is still connected, but not supplying air.This condition is REQUIRED for the ground crew that wants to disconnect the tube as they cannot do if it is pressurized.So, basically it is a correct feature that pressure is removed after the engine start.But, if someone wants to start the second engine, there must be an option to do it.This could be an added item in the menu or can be done by cycling the connected removed status for the ASU

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I don't see why should it be possible to start the No2 with ASU still connected? Just try to think of ground crew operating the ASU and the health effect of the jet blast produced by the No2 spooling up. If you need an Air Starter because your APU is INOP then it's gonna be a No1 -> crossbleed No2 start IMO. I think it's been modelled correctly/logically but as I said it's only my opinion...

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I don't see why should it be possible to start the No2 with ASU still connected? Just try to think of ground crew operating the ASU and the health effect of the jet blast produced by the No2 spooling up. If you need an Air Starter because your APU is INOP then it's gonna be a No1 -> crossbleed No2 start IMO. I think it's been modelled correctly/logically but as I said it's only my opinion...
You're rigt, but if all precautions are taken and the engines are running in idle thrust a mechanic or an handling person can walk under or near the fuselage without great risks.It is also a procedure in case you have a failed starter valve wich need a mechanic to be at one side of the engine (internal for the right one) with a Key that manually open it. After the starting procedure the mechanic will do the same path of a potential ground handling person who wants to remove the tube.For sure it exposes personnell to an added risk, and it should be avoided. But, functionally speaking, the ASU cold be used for both engines.

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I believe you daviersoft, I just remember the twisting feeling in my stomach when I walked around an engine after the a/c have stopped at the gate. It wasn't too comfortable but it might be just me being too precautious... Maybe that's why I'm not an engineer who disconnects ASUs. :)

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