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19AB67

Centre fuel tank switches ON?!

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Hi folks, 

 

whenever the the centre fuel tank is not empty after refueling, the centre fuel pump switches are set ON. 

Is this a feature of the aircraft, or a little tweak of PMDG in order to ensure that the Centre fuel tank gets empty first? 

 

If the latter is true, this is a kind of help we jockey actually don't want, do we? 

 

Thanx in advance. 

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Is this a feature of the aircraft, or a little tweak of PMDG in order to ensure that the Centre fuel tank gets empty first?

 

I think it was designed that way by PMDG. The real NG does not automatically change the switch position.

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Even better. With less than 1000kg in the centre tank, you should have the pumps off for takeoff in most SOP's that I'm aware of. (so you don't empty the tank before the Climb checklist ;) )

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I think it was designed that way by PMDG. The real NG does not automatically change the switch position.

 

Then I kindly request that this "feature" be removed. I want to manage the switches myself.

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Then I kindly request that this "feature" be removed. I want to manage the switches myself.

 

Right. 

 

Captain Randazzo, 

 

please remove it from all models 737NGX, 777...   8^)

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Then I kindly request that this "feature" be removed. I want to manage the switches myself.

 

 

Right. 

 

Captain Randazzo, 

 

please remove it from all models 737NGX, 777...   8^)

 

It was added a while back, and there was already several forum discussions about it.  You can still manage the pumps yourselves - just flip the switches on, or off.

http://forum.avsim.net/topic/361988-center-tank-fuel-pumps

http://forum.avsim.net/topic/368039-possible-of-fuel-pump-bug

 

Even as someone who normally goes on rants about realism and proper procedure, I feel that it's not that big of a deal.

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Kyle, I love your new signature!

 

Thanks Thomas - I figured it was necessary, as I tend to get adverse reactions.  Haha.

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It was added a while back, and there was already several forum discussions about it.

 

Damn, I have checked for earlier threads... to no avail...

 

 


Even as someone who normally goes on rants about realism and proper procedure, I feel that it's not that big of a deal.

 

I agree, but why not omitting an extra piece of logic, if nobody asked for it? 

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Damn, I have checked for earlier threads... to no avail...

 

The two more prominent posts were linked in my post above.

 

 

 


I agree, but why not omitting an extra piece of logic, if nobody asked for it?

 

I'm with ya, to a certain degree.  I don't think there's a real need to have it there, but I also don't think it's worth it to go remove it.  I think it was an effort made to eliminate the issues of those who wouldn't bother to read the manual pertaining to fuel loading/use.

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The two more prominent posts were linked in my post above.

 

Yup, I've read them now. I wonder why I haven't found them by the search function on Sunday. 

 

 


but I also don't think it's worth it to go remove it.

 

True. Hope they haven't spend the effort to implement it on the triple seven. 

 

(N.B. Have you had the time to check the 777 braking action screenshot in Capt. Randazzo's thread, I mean the allusion a pecularity? If so, please answer there  8^)

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The 777 is more automated than the 737. Center fuel pumps turn off automatically when empty I believe? They might turn on as well.

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Center fuel pumps turn off automatically when empty I believe?

 

Depends on what's installed in the aircraft. There are birds that require the crew to turn off the center fuel pumps when the message "FUEL LOW CENTER" EICAS message is displayed. Some may automatically shut off.

 

 

 

They might turn on as well.

 

Not automatically. If there is more than 10,500 pounds of fuel in the center tank, the crew is to turn on the fuel pumps. If there is less than 10,500 pounds, the fuel pumps are turned on above 10,000 feet.

 

In some other birds, the fuel pumps are turned on if there is fuel in the tank.

 

If the message "FUEL IN CENTER" message appears, the fuel pumps are to be turned on.

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it is realistic if you put gas in the center tanks the pumps need to prime

 

grenade launched, leaving now!

 

Eric W

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This was posted here a while ago.

NsUXNVB.jpg

 

Although I really don't see a point in leaving one pump on and the other off, because it creates an imbalance in the main tanks.

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because it creates an imbalance in the main tanks.

 

Huh?  I was under the impression that it's just one tank.  The second pump is just there to toss out fuel at a higher rate.

 

The one on and one off would only provide less fuel from the main tank to supplement the fuel from the wing tanks, that's all.

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Huh?  I was under the impression that it's just one tank.  The second pump is just there to toss out fuel at a higher rate.

 

The one on and one off would only provide less fuel from the main tank to supplement the fuel from the wing tanks, that's all.

Well, it did so for me. One time I've used this method and I had imbalance between two main tanks. After that I've only flown with center fuel pumps 2*on/2*off. I could have done something wrong, though.

Have you tried it?

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I could have done something wrong, though.

 

That's my suspicion. The center tank is one tank with two pumps. The properties of liquid dynamics would prevent an imbalance from occurring in a single tank. The use of one or two pumps on a single tank of fuel shouldn't create the imbalance you're referring to.

 

What "main" tanks are you referring to?

There's the center tank and the wing tanks. If you had an imbalance in the wing tanks, it may be because you didn't open the crossfeed for the one on / one off configuration. Take a look at the schematic below:

schemefuel.gif

 

Note that the fuel pumps feed different sides from that tank. Without the crossfeed on, you'll get an imbalance in the wing tanks.

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Even better. With less than 1000kg in the centre tank, you should have the pumps off for takeoff in most SOP's that I'm aware of. (so you don't empty the tank before the Climb checklist ;) )

I presume you mean 1000lbs or 450kg? If so, that is sort of correct. More accurately, the center pumps are not to be used with less than 450kg in the center tanks on the ground. In either case (air or ground), the main tanks must be scheduled to be full (read 'planned' or 'intended') with more than 450kg in the center tank - in other words the center tank pump switches must be on with more than 450kg. This can lead to  Master Caution Fuel annunciation on takeoff when the fuel sloshes to the back of the tank, which should be briefed to prevent an unnecessary RTO! Some guys just switch the centers off for take off with less than less than 1000kgs to prevent this.

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Note that the fuel pumps feed different sides from that tank. Without the crossfeed on, you'll get an imbalance in the wing tanks.

Yup, that was my mistake, I had crossfeed on "off".

And by main tanks I was referring to wing tanks.

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The reason there would be a fuel inbalance with just one center pump on is not because there is an inbalance in the center tank but a fuel difference between the wing tanks. Since the aircraft draws fuel from the center tank first if a center pump is on, if the left center pump is on and the right center pump is off - the left engine will draw fuel from the center tank while the right engine will draw fuel from the right wing tank resulting in the imbalance.

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Spot on for John and Kyle :) Except on the ground, engines shutdown, APU on with with > 450kgs when using a single center tank pump (the left one) will prevent an imbalance.

 

FWIW with regard to fuel balancing in general, in reality and in flight, main tank imbalances in the NG only really happen when single engine. The Classic however was a different beast, just about every flight could utilize fuel balancing to some degree. It seems the EECs in the NG do a great job compared to the Classic's PMCs.

 

Also, checkout the QRH LOW FUEL checklist for another not too uncommon reason to use the crossfeed in flight.

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This was posted here a while ago.

NsUXNVB.jpg

 

Although I really don't see a point in leaving one pump on and the other off, because it creates an imbalance in the main tanks.

 

I love this table, it helps simplify the rules I studied in the PMDG manuals.  I used to be very vigilant about the center tank switches when I flew the iFLY NG and when the PMDG NGX was first released, but since I started using FS2crew, I basically follow the SOP it uses which dictates that has the copilot leaves the center tanks on during all phases of flight until the tank is empty.  I am starting to simulate Alaskan Airlines operations, and was curious to know what their center tank policy is.  Do they use the automatic shutoff policy per FS2crew, or should I use the policy listed in this table instead?   I'd imagine it may be the latter, since they have the old classics in their fleet and I suspect crews fly both the classic and NG?   

 

I would like to get into the practice again of monitoring the center tank, but only if the airlines I simulate use it as SOP, and I have no idea which airlines do follow these rules.

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I love this table, it helps simplify the rules I studied in the PMDG manuals.

Interesting. I wasn't aware how complicated this was before I started with the Boeing. I believe those ADs are now out of date. I could be wrong, but all NGs have been modified with reliable auto-shutoff center tank fuel pumps. I don't really know the history of this, but suffice to say that the PMDG manuals describe different before takeoff procedures depending levels of compliance to this AD. The up to date procedure is the one entitled "Alternative Method of Compliance" which is the simplest and makes the above table redundant.

 

The logic of the center fuel pumps with PMDG should be that they auto shutoff after a short time with the LOW PRESSURE light illuminated. If fuel is added, they should require turning OFF then ON to extinguish the light. This is unlike the behavior of the main tank pumps.

 

In the most basic form the current procedure is - Ground: Mandetory OFF if <460kg. All other phases of flight: Mandatory ON if >450kgs. Otherwise, as required.

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