"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?"No, Paul...The engines are started with pneumatics (compressed air from an external source, the APU bleed system or the bleed system of another engine). The compressed air is fed into a starter motor... i.e. turbine which converts air pressure into mechanical (rotary) movement. This mechanical movement is transferred to the engine N2 rotor via a gearbox. When the N2 starts spinning, it draws air into the engine (this is why you see the N1 indications also rise... even before you add fuel/ignition). When fuel and ignition is added, the engine accelerates under a combination of starter power and it's own power. At a certain N2, the starter is disconnected."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."The fuel cutoff levers control ignition as well as fuel. Before you move these, you are _not_ introducing fuel and fire into the combustion chamber of the engine. You could run your tank pumps all day and not get a single drop of fuel into the engine. The starter is only spinning the engine N2 rotor. You would get a bigger bang/fire if you turned the start switch and a few seconds later lifted the fuel cutoff levers to IDLE (before the airflow through the engine had time to build up."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."It _has_ happened during engine maintenance checks (fortunately not to me)."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."As I said before, the starter is pneumatically driven, not electrically driven. PMDG is correct. Perhaps you should check out a few of the links provided in this thread for a better understanding of the 737NG. IMHO, you are giving PMDG a bad name without checking your facts.Rgds.Ian

"...and less so on the 'prong' and the QANTAS self image of being 'Lord of the Skies'"Hey... my airplane is bigger than your airplane! (I don't know about my prong, however) :-)A little less inter-airline rivalry please... or I'll tell my Mom to come 'round and beat you up...So there!CHeeRs.IAnP.S. As Shakespeare once said... "One F/O does not an airline make" ;-)

OK, so sorry, I realise the engines are started on air bleed, becuase when I first did the tutorial I couldn't get the engine 2 started using the setting in it, and one of my first thoughts was to override the cross bleed value from auto to open, and instantly the engine spooled up.My comments about the ground power disconnecting before you get a single engine up and running are valid, I think. Although, FS2004 doesn't provide ground air, so I suppose we would have to have the APU gen on anyway.

"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...... My comments about the ground power disconnecting before you get a single engine up and running are valid, I think. Although, FS2004 doesn't provide ground air, so I suppose we would have to have the APU gen on anyway."In the above, Paul, are you saying that you are you trying to start the engines with air from the APU and electrical power from an external power source?If so, I'd say you would be correct about the Ext Power. It should not trip off. Perhaps PMDG has programmed this logic for convenience, since we have no direct way of switching off/on external power (other than setting the park brake). There are very few automatic electrical power transfer operations on the real NG.However, I don't think this necessarily means that the engine start would be aborted. Just bear with me for a while... I have to consider the behaviour of the following bleed air valves with power removed from the main busses (and only Battery/Standby Power available).1. The APU Bleed Valve (This is controlled by the APU Controller which can be powered by the (Switched) Battery Bus. This is required to be open to get bleed air into the left side of the main bleed air duct).2. The Bleed Isolation Valve (This is powered by the main busses, but it should remain in the last position... It shouldn't close if it was open beforehand) This valve is required to get bleed air to the right bleed duct to start the right engine.3. The Engine Start Valves (These are powered by the Battery Bus)I would also have to look at the engine ignition system and the fuel delivery system, but I'm pretty sure that these would operate with Battery/Standby Power (otherwise you couldn't restart your engines in flight if you had a dual flameout).So the only big question that remains is why PMDG chose to trip off EXT Power when the start switch is turned...I'll let you know if I find an answer ;-)Cheers.Ian.

"I'd say you would be correct about the Ext Power."Then again, I could be wrong about you being right. I have been told that at least one airline's 737's will do some strange things with Ext Power depending on which engine you start first.Cheers.Ian.

Well then please explain me why there is an electrical fuelpump.Wothan

"Well then please explain me why there is an electrical fuel pump."Firstly, there are no gravity feeds from the Center Tank, so you need a pump or two to empty this tank. Secondly, the electric boost pumps are there to assist the engine fuel pump at times of high demand or when circumstances are not ideal.As mentioned in previous threads, sucking fuel out of the tank using the engine pump can aerate the fuel (and MAY cause starting problems). Unfortunately, we don't have any statistics on this.... You may be able to start the engine 99 times without any problems, but the 100th may not go so well.Hope this makes sense.CHeers.Ian.

If there is Gravity feed on the engines and the fuel pumps are not required to turn on, why they actualy make those pumps then by Boeing???You don't need to turn them on, so wats the use of it???Is this also the case with the B744???

I belive the electrical pumps are in or close to the fuel tanks, to prevent caviation in the suction line (feed line for the engine) and ensure feed pressure for the engines in low G situations as well. Remember there is a considerably lower atmospheric pressure when the plane is at cruising altitude, this will make caviation more likely. If there is caviation in the feedline for the high press pumpes you run the risk seize and excessive wear. If the caviatation is bad enough you risk fluktuations in the high pressure line with the result of an unstable flame and the risk of a flame out. Therefor it's "smart" to put a feed pump at the tank, producing a higher pressure in the feed line, to prevent caviation, even though it could work with out.CheersPeter Nielsen

"If there is Gravity feed on the engines and the fuel pumps are not required to turn on, why they actualy make those pumps then by Boeing???"Ramon....Please read our responses again...carefully... I'm pretty sure we just gave you lots of good reasons. What part didn't you understand?CHeers.Ian.

Hej Ian and "goddaw" Peter (Goddaw Peter means goodday in Danish).Yes both of Your comments make sense, didn

Electrical fuel pumps are certainly neccessary and they cant be left out from a Boeing. If you CAN GET the engine running without electrical fuel pump, it doesnt mean that you dont need them at all. If you have 140 passengers on board, you must back up everything and ensure that systems will run fine and fuel gets to the engines even with low G and so on. You turn fuel pump on with Piper Cherokee too. Does it mean that engine will not run without Fuel Pump? No. Its just IN CASE something will happen.

Ok thank you, but is that also the case with the B744????

Im pretty sure that yes. All turbofan engines should have the mechanical pumps implemented. If you example loose the electrical power, does it mean you will loose all engines at the same time? Im afraid not :)

Ok thank you very match, but I know that if you select a pump on or off then that respective pump will work or not, so this pumps are working on a high pressure system, the pump with the most delivering pressure feeds the engines.