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Guest james320

Engines will start with fuel pumps off!!

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Engines will start with fuel pumps off!!I've been aware of this error for some time (engines shouldn't start without a supply of fuel) but I'm more surprised that it wasn't addressed in the recent update?James Stevensonhttp://www.virtualaviation.co.uk**In 737-800 full-motion sim at EGKK tomorrow eve for two hours, can't wait!

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I seem to remember from another post that the engines on the NG are fed by gravity and that the fuel pumps do not have to be on for a start. However, bleed air is required.

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Interesting... I'll test out the theory tomorrow by leaving the fuel pumps off during the engine start!James Stevenson

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The operation is absolutely correct.The overhead controlled fuel pumps are the electrical fuel pumps. Each engine has mechanical, engine-driven fuel pumps that will provide suction feed in the event normal electrical fuel pump operation is not available. The engine pumps draw fuel through bypass valves located in main tanks No. 1 or No. 2.All you need is bleed air, either from the APU or from groundHopes this is explanation enough

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It's perfectly normal that the engines start with fuel pumps off. Do a search on the forum, you will find another topics discussing the reasons behind this.Tero

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>Interesting... I'll test out the theory tomorrow by leaving>the fuel pumps off during the engine start!>>James StevensonIsn't this what your post was complaining about?This behaviour is how the bird works in real life. The only way you won't get fuel for a start is if the engine driven fuel pumps have failed or the spar valve doesn't open.BTW, here's a snipet from the AOM:Fuel PumpsEach fuel tank uses two AC-powered fuel pumps, which are fuel cooled and lubricated. A single failure in the electrical system will not affect more than one pump in each tank. Individual pressure sensors monitor the output pressure of each pump.The engine-driven fuel pumps will provide suction feed in the event normal electrical fuel pump operation is not available. The engine pumps draw fuel through bypass valves located in main tanks No. 1 or No. 2. No bypass valve is available in the center tank. The main tank bypass valves may also be used for suction defueling.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

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>All you need is bleed air, either from the APU or from groundDoes the 737NG have the possibility to be fed by external bleed air? I thought it does not... Could someone confirm that or am I wrong?Markus

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>>All you need is bleed air, either from the APU or from>ground>>Does the 737NG have the possibility to be fed by external>bleed air? I thought it does not... Could someone confirm that>or am I wrong?>>MarkusSal

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