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Question about Fuel Tank/ENG

pmdg 747 fuel tank engine

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7 replies to this topic

#1 lazaroblanc

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Posted 16 August 2012 - 03:18 PM

Hi I have a short question about the Tank to Engine procedure on the 747

What happens if I dont turn of the override pumps and the x-feeds because I may be sleeping?
I want to take the 747 out for a spin from Frankfurt to Buenos Aires over night so I can sleep on the 13 hour trip and so I wouldn't be able to perform that action of switching the fuel pumps.

A quick answer would be appreciated,

Thx in advance

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#2 yos233

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Posted 16 August 2012 - 06:58 PM

Nothing. I've done it many times, you're fine.
Eric Vander
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#3 scandinavian13

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Posted 16 August 2012 - 09:57 PM

You sure about that? Won't it overdraw from the inner tanks and leave the outer tanks alone?

Kyle Rodgers

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#4 Ioan92

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Posted 17 August 2012 - 12:47 AM

Although I'm not sure what would happen because I've always done what the Queen told me to..

Leaving the pumps on won't do anything more than wearing the pumps. The specific tank is empty so why keep the pump on? (correct me if I'm wrong)

Although leaving FUEL TANK/ENG unattended seems a bad idea to be, it generates a fuel imbalance and you may end with 2 and 3 flamed out with 1 and 4 still running.

That's what I THINK happens, please correct me if I'm wrong.


Anyways, FRA-EZE is long, so you should have near a full tank of fuel. First warning will be the center pumps, the other will be many many hours later when all levels reach 13 I think.

You should be able to sleep at least 5 hours before the F T/E message.
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#5 clipper759

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Posted 17 August 2012 - 04:38 AM

You will likely have a fuel imbalance that exceeds the limitation of 6,000LBS between Inboard/Outboard main tanks after reaching "Tank to Engine". Will this have any adverse effect on the sim? Probably not. But it's not technically accurate.

You should be able to estimate the time you will reach "Tank/Eng Config" based on your present fuel flow. Then just set an alarm to come press your switches and off you go to crew rest again.

Easy as pie...


Cheers,
Randy Adams
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#6 FrankG2625

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Posted 17 August 2012 - 11:16 PM

From a real-world 747-400F FCOM about fuel imbalance:

Excessive fuel imbalance adversely affects CG, aerodynamic drag, and therefore, fuel economy. To maintain CG and reduce drag, operate the airplane within limits of FUEL IMBALANCE EICAS advisories.

Fuel may be balanced:
• between main tanks 1 and 4 by opening crossfeed valves 1 and 4, closing crossfeed valves 2 and 3, turning off the fuel pumps in the low tank, and turning off the override pumps in main tanks 2 and 3
• between main tanks 2 and 3 by turning off the fuel pumps in the low tank
• longitudinally by opening all crossfeed valves and turning off the fuel pumps in the low tanks.

Avoid conditions which require fuel suction feed, unless directed by published non-normal procedure. The fuel system should be returned to normal operating condition when the imbalance condition has been corrected.


From a real-world 747-400 FCOM about FUEL TANK/ENG:

The electrical Center Wing Tank (CWT) scavenge pump is automatically activated to pump CWT fuel into main tank 2. The pump is deactivated after 120 minutes, or no pressure, whichever occurs first.

The EICAS message FUEL TANK/ENG displays when main tank 2 quantity is equal to or less than main tank 1 quantity, or when main tank 3 quantity is equal or less than main tank 4 quantity. In the tank-to-engine configuration, the main pumps provide fuel to their related until engine shutdown.


But we knew that. The question is of course, what happens if you ignore the FUEL TANK/ENG caution on the EICAS? A UK CAA report on British Airways G-BNLG which lost an engine in the initial stages of the flight but continued to London (from LAX in 2005) on three engines may shed some light:

The control of fuel usage is largely automatic, once the system has been set before takeoff by selecting all pumps ON and all crossfeed valves OPEN. The system causes the horizontal stabiliser tank, the centre tank and the reserve tanks to empty in turn, and then for fuel to be fed from the inboard main tanks, using the override/jettison pumps to overpower the main pumps in the outboard main tanks. When the fuel quantity in an inboard main tank becomes approximately equal to that in the adjacent outboard main tank, the crew is provided with an EICAS message ‘FUEL TANK/ENG’; this occurs at a total fuel load of around 55 tonnes (13.75 tonnes/tank). At this point the crew is required to select manually Crossfeed Valves 1 and 4 Closed and Tank 2 and 3 override/jettison pumps Off, effectively causing each engine to be supplied from its respective tank.

The design intention is that no further crew action is required except in response to EICAS messages indicating the abnormal conditions of fuel tank imbalance or low fuel quantity. Imbalance is not subject to Flight Manual limitations but should generate EICAS messages to alert the crew, as follows:

The design intention is that no further crew action is required except in response to EICAS messages indicating the abnormal conditions of fuel tank imbalance or low fuel quantity. Imbalance is not subject to Flight Manual limitations but should generate EICAS messages to alert the crew, as follows:

1. ‘FUEL IMBALANCE i-4’: There is a fuel imbalance of 1,360 kg between main tanks 1 and 4.
2. ‘FUEL IMBALANCE 2-3’: There is a fuel imbalance of 2,700 kg between main tanks 2 and 3.
3. ‘FUEL IMBALANCE’: This message is effective only after the ‘FUEL TANK/ENG’ condition and indicates that there is an imbalance of 2,700 kg between inboard main tanks (2 and 3) and outboard main tanks (1 and 4).

Some differences were noted between the Operations Manual issued by the manufacturer and that issued by the operator, relatng to fuel balancng. The operator’s manual expanded on the information in the manufacturer’s manual providing practical advice on fuel balancing. However, the operator’s manual required the use of the override/jettison pumps to correct any imbalance between main tanks; if this was not possible, the main pumps in the low quantity tank should be switched off. The manufacturer made no reference to the override/jettison pumps and required that the main pumps in the low tank be switched off in the event of an imbalance between main tanks. The rationale behind the manufacturer’s procedures was that the balancing procedure was the same, regardless of whether the fuel quantities had decreased below the override/jettison pump standpipe level or not.


I think to sum it up, what would happen if you ignored FUEL TANK/ENG? Depending on the length of the cruise you could suffer a flame-out, but most likely you'd just end up with a FUEL IMBALANCE scenario. This in and of itself has little bearing on maneuverability, but does affect stresses on the airframe and landing gear. So since PMDG didn't model stress accumulation, the shortest answer would be: NOTHING!

Phew, that was my research done for the day. ;)


If you want to read more about NLG: http://www.aaib.gov....-BNLG 06-06.pdf
Frank Grivel
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#7 FlyVFR

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Posted 18 August 2012 - 11:04 AM

FS2Crew copilot for the -400X with switch them for you while you sleep soundly through the night.

I do it all the time.
Chuck Biggins

#8 mareng69

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Posted 20 August 2012 - 04:54 AM

FS2Crew copilot for the -400X with switch them for you while you sleep soundly through the night.

I do it all the time.


Where? I know co-pilot in NGX does this, but where or how do you enable this feature in the 747-400X?

Jeff Smith

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