Hi !I noticed something strange, when i turn off all fuel pumps on Overhead Panel, the engines are still running. I can also start the engines when all fuel pumps are off.This is not correct, is it?Marcello

Yup correct...Gravity feed... if there's some fuel in wing tanks...

I have a friend who tried this out who is also an FO on a Qantas 744 and he is very much into detail. When he found out the PMDG 737 doesn't need to have fuel pumps on, he said he didn't want to fly it anymore. Not sure if he's correctly distinguishing between the 744 he flies and the 737. I'm only going by what he said.Someone on the development team want to expand on this??Goran

hi!Nice zo hear that i'm not the only one with this problem.I think this is something that has to be fixed very soon, otherweise it would be a step back, strange that nobody has mentioned it in the AVsim Review....marcello

>hi!>>Nice zo hear that i'm not the only one with this problem.>>I think this is something that has to be fixed very soon,>otherweise it would be a step back, strange that nobody has>mentioned it in the AVsim Review....>>marcello>I think that the point is that the real plane is able to have gravity-feed get the fuel to the engines, at least while sitting still. May not be the most reliable, but it is my understanding that it's on purpose, and not a mistake.Preston G.

The real 737NG will run without fuel pumps on. PMDG modelling is correct.

The aircraft main engines will run fine without fuel pumps or with Low Fuel Pressure lights illuminated.From the QRH:"Note: At high altitude, thrust deterioration or engine flameout may occur"Goran: May I suggest that your 74 FO friend get more of a grip on reality and less so on the 'prong' and the QANTAS self image of being 'Lord of the Skies' :-xxrotflmaoATB,

As far as I know there are both electrical and mechanical fuelpumps for each engine.The electrical fuelpumps are operated via the switches on the overheadpanel and the mechanical are driven directly by the engines. As long as the engines are running the mechanical fuelpumps will pump fuel to the engines, furthermore the engines are gravity fed, so even if the engines are stopped they can be started with the fuel coming by gravity from the fueltanks, allthough not with as high a pressure than if the mechanical and/or the electrical fuelpumps are running. So the mechanical driven fuelpumps is present to ensure that the engines recieve enough fuel and the electrical fuelpumps are used as a safety measure if the mechanicaldriven pumps fail.Standard ops is to have the electrical fuelpumps running in all phases of flight.Wothan

Wothan,Spot on.. couldn't have put it better myself.Rgds,

"I have a friend who tried this out who is also an FO on a Qantas 744 and he is very much into detail."Hopefully you've misunderstood something he has said. Ask him again and if he says the engines won't start, tell him to ask his engineers about gravity or suction feed. I've seen engines on a REAL 744, and a few other Boeing aircraft as well, start without fuel pumps with no problems at all. There are even special fuel lines (pipes) in the fuel tanks which bypass the pumps to help this happen. The engines also have their own small pumps which suck the fuel out of the tanks (with the aid of gravity). If you had a 4 engine flameout in the air (say due to volcanic ash) how are the pilots going to restart their engines if they had to rely on their tank pumps? (The engine generators would be dead and the pumps can't be powered by Battery/Standby Power).It's common sense... If engines couldn't start without pumps, they wouldn't be safe to fly.Cheers.Ian.

"furthermore the engines are gravity fed, so even if the engines are stopped they can be started with the fuel coming by gravity from the fuel tanks,"If, by "engines are stopped", you mean that the engines are not turning, then I would have serious doubts that you could start an engine like this. The fuel pressure going into engine combustion chamber has to be fairly high to get a proper spray pattern. The engine also has to be spinning to ensure a proper air flow through the engine .... otherwise you would just end up with an engine fire.For info, the NG engine mechanical fuel pump is divided into two sections (high and low pressure). i.e. it is actually two pumps in one. According to the NG Maintenance Manual....The low pump (centrifugal impellor type) can operate with low inlet pressure (and with fuel that is part liquid and part vapour). It produces a low pressure discharge which won't damage heat exchangers. The high pressure (positive displacement gear) pump is necessary to give a strong combustor spray pattern and to operate the engine actuators that are part of the engine servo system (for operating moveable engine inlet guide vanes, etc).I think gravity-fed fuel would have trouble getting through both engine pumps if they were not spinning. If it did, you would most likely end up with an engine fire because the fuel is not being delivered to the combustion chamber properly and there is no air flow through the engine.I may have misunderstood what you were trying to say, however.Cheers.Ian.P.S. Real pilot Brad "Zapper" is agreeing with what you are saying, but I'm sure he will agree with me on what I am saying also ;-)

Yes offcourse the fuelpressure to the engines should be rather high, but think again, on the ground the engines is started by air coming from either the APU, the other engine or from ground supply. once the engine is turning the mechanical fuelpump will start pumping fuel to the engine. In flight even a stopped engine is not stopped but the compressor will be spinning thus driving the mechancal fuelpump.Some very nice diagrams showing both fuel, electrical, hydraulic and pneumatical systems on the boing can be found on this site: http://www.b737.org.uk/aircraftsystems.htmWothan

"Yes offcourse the fuel pressure to the engines should be rather high, but think again,..."I think there has been a misunderstanding here... I know how an engine works... I just wasn't sure that you knew.You said...."so even if the engines are stopped they can be started with the fuel coming by gravity from the fuel tanks,"From this, I thought you were trying to tell everyone that you could start an engine simply by pouring fuel into it. I was trying to explain that you couldn't.Cheers.Ian.

When you start the engines they are spinning on Ground or Battery power aren't they? So the engine mech fuel pumps would be in operation?A thing I have found with a few models, correction all models in FS2004, is that you get away with diasters time and time again and taxi out for a safe flight after you would have probably blown the stand to pieces.As example. Switch the electric fuel pumps on for 2 minutes.... starter on, but (I know the NG doesn't allow this) leave the ignition off for a while. Build up a nice bomb of fuel in the engine and then hit the ignition. I'm just thinking out loud, but would this not be akin to holding the gas button in on a lighter in your pocket and then flicking the flint? Try this and see what happens. Don't worry, the hair will grow back and warm water and patience will get the melted polyester off your hand.I suspect that filling the combustion cans in a real jet with fuel, because the attactive blonde swerdie is bending over beside you, could result in an egine fire or exposion when you hit the igition.Drifting from topic, but, in the PMDG if you start on ground power, the instant engine out spins up, the ground power is discoed, if you dont have the gen on everything should die, probably including the engine starter. I find you get away with this on most models and I have only once found a model that simulate gen power in a fashion that appears real... The Dash 8 Q300 from the avsim library. When landig and you hit the prop reversers the landing lights and cabin lights dim, flicker and come back up again the master caution lights up briefly as the generators register low output and this is repeated when you disco the reversers. I persume this is to model the changing prop RPM during the manouver, although Im curious as to why the gens are not on the turbine shaft, as opposed to the prop shaft.

If the engine driven mechanical pump fails, forget about running that engine as it will automatically shut down due to lack of output pressure and flame out.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg