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suchw

air unit start - help

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Hi I am trying to start the NGX via the air unit, always have plenty of duct pressure for one engine to start but when trying to start the other engine air duct pressure drops and cant get past 19 % N2, anybody done this, thanks

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make sure both packs are off and isolation valve is set to auto. You could always cross bleed to start the other engine. Also, which engine are you starting first? it would be preferable to start engine 2 first. If you give the engine with 19% fuel, it should still start. Mitch Bowman

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i have tried starting either, i find I can start the second if i start it straight after the first but if i let the first engine stabalise i cant get a start on the second engine if if i introduce the fuel in a 19, wont go past 19%

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i have had the exact same problem i had to start the apu and finish with an apu start, i think its a bug too ive tried different combinations of pack and bleed configurations nothing works, only one engine can get started on grnd start

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Both engine bleed valves should always be on during an engine start. Try once with an open isolation valve, and then with a closed iso valve. Mitch Bowman

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Both engine bleed valves should always be on during an engine start. Try once with an open isolation valve, and then with a closed iso valve. Mitch Bowman
Ohh no no no no! The engine bleed valves you see on your overhead panel should be closed during the start. They are not part of the engine air starter ducting at all. The EGV's on the upper panel allow air from the 5th+9th stages (well on the 3-4-5's...pretty sure they are the same in the new NG's) into the pneumatic system. You don't want that air that's supposed to be going to the combustion chambers getting bled off prematurely. Hopefully it's okay to post this here: from http://www.b737.org.uk/pilotnotes.htm EDIT: I guess it's redundant as Andrea described below :( heheschem_pmeumatic.jpg

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once one engine started disconnect air cart ensure clear behind and run up the live engine to 40 % n1 then start the other engine, this way you do not have to start the APU if you dont want too

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Bleed valves are electrically controlled and pressure operated valves. This is to say that only air pressure can open them 8they are spring loaded closed)Check valves also prevent airflow going back to the engine.For starting the bleed valve regulator solenoids are de energized by the starter valve, so there will be no bleed from 0 to 55% of N2.After 55% of N2 the bleed will open if already selected open, and no damage to the engine will be made.Normally the bleed are left to ON as they are also part of the isolation valve auto logic.For ground start, I don't know why it doesn't work for the second engine start, maybe it simply automatically disconnect or turn off after the first engine start.Remember that the air cart is connected on the right side of the plane, so it is necessary to start the LH engine to prevent possible operator injestion by the right engine when the operator removes the air cart tube.After the engine is started, you will need to increase its power to get more than 30psi in the pneum. ducts. After that the second engine can be started.To check if it is a bug or simply that the cart self exclude itself, after the first engine start, increase power to it, if pressure increases, the cart was disconnected, try also by putting the running engine bleed off, in that case, if there is no pressure, the cart is disconnected, if you get another 19% of N2 there is a bug somewhere, report here and I will try to replicate the issue. ;)

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Man, you guys make this complicated. Are you guys following the checklists? If the APU is available, you'll use that to start both engines. All of the bleed switches will be open during the starts. After the starts, the APU comes off, the packs come on and the ISO VALVE is AUTO. If the APU is not available, you'll start from a ground source of air, either a bottle or a ground air unit. Follow the SUPPLEMENTAL OPERATIONS information for that. Eng #1 is started at the gate, #2 is started via cross-bleed.

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Ohh no no no no! The engine bleed valves you see on your overhead panel should be closed during the start. They are not part of the engine air starter ducting at all. The EGV's on the upper panel allow air from the 5th+9th stages (well on the 3-4-5's...pretty sure they are the same in the new NG's) into the pneumatic system. You don't want that air that's supposed to be going to the combustion chambers getting bled off prematurely. Hopefully it's okay to post this here: from http://www.b737.org.uk/pilotnotes.htm EDIT: I guess it's redundant as Andrea described below tongue.png heheschem_pmeumatic.jpg
The bleed valves are supposed to be on! the packs are supposed to be off Mitch Bowman

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Making it way to difficult. im still tripping over the guy who posted the whole pneumatic schematic and it's not even for the NG's lol

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lol it's close...but I got it wrong anyways.... Andrea explained the thing's idiot proof anyways...the bleed valves for the engine won't open till 55% anyways so it doesn't matter what the EGV switch is selected anyways. haha....although the pneumatic's are very similar to the NG's anyways. Lemme see if I can dig up a NG pneumatic thing...actually...why bother hahah

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To simplify everything here and give a summary of the procedures: Packs should be off and bleeds on. Start #1 first. Disconnect the ground cart. Increase power on the #1 engine until you have 30 psi (about 40% and remember the Isolation valve should be open on the air panel). Start #2. And as mentioned, SP 7.5 in the FCOM Vol. 1 has the air cart and cross bleed start procedures. (Both are used when starting from the ground cart.)

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