dores893

RSV Fuel Tank Surprise

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I'm still breaking in the 748 and encountered something I haven't seen before.  The tanks were set up for a short haul flight with more fuel in 2&3 than 1&4.  The center tanks were empty.  As on the 744, I set the pumps on for every tank, turned on the xfeeds, and set the override pumps on for 2&3 so as to draw from the heavier tanks until the fuel quantify was equal in every tank.  At around cruise with plenty of fuel, tanks 1&4 were flooded with the reserve tanks.  The reserves went to empty in under five minutes, and I spent the rest of the flight burning from the outboard tanks.  The only thing I can think of that would cause this would be if I accidently set the guarded reserve transfer switch from auto to on over on the FO's overhead panel (not something I remember doing).

Do you guys agree with that logic or can you think of others ways to draw from the reserves so early in the flight?  My understanding is that they aren't usually touched until you are very low on fuel.

 

Jimmy Helton

KBNA

Edited by dores893
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Hello Jimmy

The Fuel Management System will Automatically Transfer Fuel from RSV tanks to Outboard main tanks if aircraft is not on the Ground and Outboard tanks fall below 13400 lbs of fuel.

Best Regards.

Edited by Samany69

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Would 13400 lbs be indicated as 134 or 13 on the fuel tank MFD page?  My inboards were indicating 59 and my outboards in the 60s (I had accidently passed the equalization) when the outboards shot up into the uppers 70s from the reserves.

 

Jimmy Helton

Edited by dores893
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Also to confuse myself a bit more, it looks like from the schematics the reserves feed into mains 2 and 3.  Maybe that was altered to 1 and 4 in the 748?

Jimmy Helton

Edited by dores893

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8 minutes ago, dores893 said:

Also to confuse myself a bit more, it looks like from the schematics the reserves feed into mains 2 and 3.  Maybe that was altered to 1 and 4 in the 748?

2 and 3 on the -400, 1 and 4 on the -8.

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So it looks like I bled my reserves into 1 & 4 with well over the minimum fuel of 13.4?  Also, and I'm not sure why, the pumps and crossovers didn't pop off automatically when 1-4 were equal even though that setting was on in the FMC PMDG setup (I have since turned it off...because I'd rather do it manually).

 

Jimmy Helton

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Alright, let's go step by step.

( Boeing 747-8 )
1.it will be indicated 13.4. 
2.Only The fuel in the outboard tanks count, not the difference of Inboard and outboard(which count for imbalance)
the indicator of Fuel mass in the Fuel Synoptics indicates remaining fuel of each tank as XY.Z which should be multiplied by 1000 by your units system ( lb or KG ).
3. the Fuel being transferred from 1 and 4 to each respective inboard tank is done only and only Manually by the Main Fuel Transfer Switch if I recall correctly and, unlike the RSV transfer mode, it does not have an automatic mode which has an Auto mode and an On(forced Transfer) mode. 
4. if you were 50s on inboards and 60s on outboards then it was definitely you who did the RSV Transfer because in the Automatic function, it only gets after your outboard falls below 13400.
5. the Override pumps and crossfeed valves only operate manually, only Automatic ( Unrealistically Automatic ) if you set the option in the PMDG Options.
6. The indication of transfer works truly fine, White Bordered arrow from RSV tank to Outboard tanks which are filled with green color shows that Fuel is being transferred from RSV tanks to OUTBD tanks and the Same arrow just tilted a bit showing up between OUTBD and INBD tanks referring to Main fuel XFER from 1 to 2 and from 4 to 3.

Edited by Samany69
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Which brings me to my original conclusion that I must have somehow set the guarded reserve transfer switch from auto to on.  I can't think of anything else that would bleed out my reserves with so much fuel in the mains.  Does that sound plausible?

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3 minutes ago, dores893 said:

Which brings me to my original conclusion that I must have somehow set the guarded reserve transfer switch from auto to on.  I can't think of anything else that would bleed out my reserves with so much fuel in the mains.  Does that sound plausible?

It is possible.
I can't see or find any other Logical reason. Maybe or for sure Kyle or other PMDG staff will have more for you around if they look here. I am just saying what I know which is not always guaranteed to be 100% correct.

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To be honest, reading the narrative, I'm not quite following along with what happened, and I'm even less sure that proper procedures were followed. I'd need more detail to comment.

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I'm happy to clarify any points of confusion.  Can you be more specific on where I should elaborate?  Basically, the reserve tank fuel moved into tanks 1&4 when they had around 60,000lbs of fuel in each main tank.  This caused a quick surge in tank quantity that caused a major fuel imbalance.  It wasn't something that I asked the tanks to do at least not intentionally.  At the time, the tanks were set up to draw only from 2&3 until such time as 2&3 equaled 1&4.  I can elaborate on that setup if necessary.  The question is what could move the reserve fuel so quickly into mains 1&4 under conditions other than the aircraft logic (i.e. less than 13.5 in the tanks).

 

Jimmy Helton

Edited by dores893
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29 minutes ago, dores893 said:

I'm happy to clarify any points of confusion.  Can you be more specific on where I should elaborate?  Basically, the reserve tank fuel moved into tanks 1&4 when they had around 60,000lbs of fuel in each main tank.  This caused a quick surge in tank quantity that caused a major fuel imbalance.  It wasn't something that I asked the tanks to do at least not intentionally.  At the time, the tanks were set up to draw only from 2&3 until such time as 2&3 equaled 1&4.  I can elaborate on that setup if necessary.  The question is what could move the reserve fuel so quickly into mains 1&4 under conditions other than the aircraft logic (i.e. less than 13.5 in the tanks).

How are you loading your fuel into the aircraft? Are you using any VA programs, or third party apps that set pax counts, fuel values, and so on?

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I'm loading fuel and payload from the FMC.  I start cold and dark.  I've noticed a few more nuances of the 748 that I'm trying to confirm.  Not only do reserves flow into tanks 1&4, but per the non-normal checklist, I believe you balance 2&3 with 1&4 plus the reserves?  And, if you don't, 2&3 will suck out your reserve fuel.  I need a few more flights to test that hypothesis.  She is a different bird than the 744 for sure.

 

Jimmy Helton

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11 hours ago, dores893 said:

I'm loading fuel and payload from the FMC.  I start cold and dark.  I've noticed a few more nuances of the 748 that I'm trying to confirm.  Not only do reserves flow into tanks 1&4, but per the non-normal checklist, I believe you balance 2&3 with 1&4 plus the reserves?  And, if you don't, 2&3 will suck out your reserve fuel.  I need a few more flights to test that hypothesis.  She is a different bird than the 744 for sure.

 

Jimmy Helton

The Introduction has a section on differences between the -400 and -8 and the fuel system is one of them.  Reserve tanks are associated with the outboard mains, not the inboard mains.  The aircraft is very good at giving you EICAS messages when something needs to happen to fuel configuration.  If you load enough fuel, you will feed four engines from two inboard mains (2 3) during climb and cruise UNTIL the EICAS indicates TANK/ENG and then you open the crossflows 1 2 and turn off override 2 3 such that each main feeds it's engine.  You only note the value of the reserves 1 4 when adding their value to mains 1 4; otherwise, you have no control over them.  If you configure TANK/ENG before the EICAS message, even the the loads are exactly equal between outboards main+resv and inboard mains, the airplane will not be happy and will continue to give you fuel configuration messages until you wait until after the EICAS says its time to reconfigure.

Very complete and concise operating instructions are in the FCOM.

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Tonight I decided to try to balance 1&4 plus the reserves with 2&3.  That was the point where I turned off crossfeeds and overrides.  When I did that, each tank was balanced and the aircraft was happy.  No more EICAS messages.  Yes, the 748 made me do math...in my head.

I think we can mark this closed.  I now know the reasons for the EICAS messages and why I bled my reserves....I didn't add them to 1&4 when balancing the fuel.  It's possible to start with more fuel in the outboards plus reserves than the inboards when you are doing a short hop.  That sets you up for a lot of EICAS fuel messages until you draw from the right tanks to get your balance.

PMDG did an amazing job on this aircraft.  

 

Jimmy Helton

Edited by dores893

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35 minutes ago, dores893 said:

I think we can mark this closed.  I now know the reasons for the EICAS messages and why I bled my reserves....I didn't add them to 1&4 when balancing the fuel.  It's possible to start with more fuel in the outboards plus reserves than the inboards when you are doing a short hop.  That sets you up for a lot of EICAS fuel messages until you draw from the right tanks to get your balance.

Okay, this one I have to ask....how are you even loading the fuel. As far as I'm aware, the ONLY way to correctly load fuel is via the PMDG fuel loader in the FMC. The fuel loading issue shouldn't be happening in the first place.

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11 hours ago, dores893 said:

Yes, the 748 made me do math...in my head.

haha - yeah, the adjustment is a bit odd, but at the same time: don't try to outsmart the plane. In this case, let it prompt you for the change.

11 hours ago, dores893 said:

PMDG did an amazing job on this aircraft.  

Thanks!

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18 hours ago, Captain Kevin said:

Okay, this one I have to ask....how are you even loading the fuel. As far as I'm aware, the ONLY way to correctly load fuel is via the PMDG fuel loader in the FMC. The fuel loading issue shouldn't be happening in the first place.

You could load fuel through the EFB on the W&B calculator in the performance tab. Enter the amount you want in the tanks and hit send to aircraft. You could easily set it up to put fuel in random places and send the computer for a loop.

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5 hours ago, rgamurot said:

You could load fuel through the EFB on the W&B calculator in the performance tab. Enter the amount you want in the tanks and hit send to aircraft. You could easily set it up to put fuel in random places and send the computer for a loop.

That's not what the function is for, though, and his point isn't that.

He's asking if the OP is loading fuel via a third party app, or the sim's default fuel/payload function.

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