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Ephedrin

Is it me or is it wrong? (Fuel logic non normal checklist)

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Posted (edited)

During decent I got the EICAS messages FUEL OVRD 3 FWD and FUEL OVRD 2 FWD. 

Working through the non-normal Checklist for tank 2 it asks me to "OVRD 2 pump switch (affected pump) ... OFF."

done.

the checklist item gets checked/green and below it asks "Both override pumps in tank 2 are inoperative : yes... no... I chose no. 

Checklist complete. (green)

 

but for tank 3 it does the same until it asks yes or no and when I choose "no" it jumps to the next step that asks me to turn off the OVRD 3 AFT pump switch. I have to turn it off too to complete the checklist, although the AFT pump is still fine and gets enough fuel.

 

Do I miss something obvious or should I submit a bug ticket?

0dCSFwo.jpg

 

W7vqZYK.jpg

Edited by Ephedrin

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3 minutes ago, Ephedrin said:

Do I miss something obvious or should I submit a bug ticket?

Yeah - you're operating the plane incorrectly, and the plane is trying to protect itself from you, and save you from yourself (sounds mean, but it's the truth - if you abuse a plane in today's age, it will do what it can to save you from yourself).

You should be in a TANK/ENG condition. This is entered when all four MAIN tanks are equal (the case in your screenshots).

The correct TANK/ENG config is:

MAIN 1 PUMPS: ON
MAIN 2 OVERRIDES: OFF (incorrect in your photo)
MAIN 2 PUMPS: ON
[Centerline tanks - ALL: OFF]
MAIN 3 PUMPS: ON
MAIN 3 OVERRIDES: OFF (incorrect in your photo)
MAIN 4 PUMPS: ON

To understand this, you have to consider the background. If you look at the FUEL page, you will see that the only pumps running all four engines, when not in a TANK/ENG condition, are the OVRD pumps in MAIN 2 and MAIN 3. These pumps are heaving fuel out of these tanks to keep all four engines running, and the reason you're running all of the engines off of these tanks is that they can hold a lot more fuel than the outboards (think of the profile of the wing here), and you want to burn that fuel off to equalize all four tanks. Once the inboard and outboard tanks are all at the same level, though, there's no longer a reason to be heaving fuel out of the tanks, so you turn the OVRD pumps off, and then set the engines up in a way that they all draw from their own tank (this also ensures that if there's a leak in a line between one of the tanks and an engine, you're not going to affect more than one engine, in theory).

The override pumps are there to throw out A LOT of fuel so that all four engines can be run off of those pumps, supplying from those inboard tanks, only. Those two override pumps are doing the same work that would otherwise be done by four pumps (on each side of the plane). When you get to TANK/ENG, the proper flow is: OVERRIDES OFF, then turn off the outer crossfeeds (the part you seem to be already doing) OFF.

This is something I explained in this thread quite a while ago, and it is also explained in multiple places in our 744/748 documents: 

 

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19 minutes ago, Ephedrin said:

During decent I got the EICAS messages FUEL OVRD 3 FWD and FUEL OVRD 2 FWD. 

Working through the non-normal Checklist for tank 2 it asks me to "OVRD 2 pump switch (affected pump) ... OFF."

done.

the checklist item gets checked/green and below it asks "Both override pumps in tank 2 are inoperative : yes... no... I chose no. 

Checklist complete. (green)

 

but for tank 3 it does the same until it asks yes or no and when I choose "no" it jumps to the next step that asks me to turn off the OVRD 3 AFT pump switch. I have to turn it off too to complete the checklist, although the AFT pump is still fine and gets enough fuel.

 

Do I miss something obvious or should I submit a bug ticket?

 

 

 

Marc. good catch. I will alert the dev team 🙂

 

However why you have the ovrd pumps operational in tank 2 engine?

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Thankls for the detailed explanation, Kyle.

After reaching cruise altitude my outboard tanks were in sum equal to the inboard tanks, so I turned off the X feed and the OVRD pumps, as learned. But then the airplane complained about the OVRD pumps being off and I turned them back on. 

I will take a look at this in the next flights, maybe it's my panel state or something else.. If I note something odd I will come back to this. 😃

Cheers 😄

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5 minutes ago, Olympic260 said:

Marc. good catch. I will alert the dev team 🙂

 

However why you have the ovrd pumps operational in tank 2 engine?

sry I was typing when you answered.. read above please 😄

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1 hour ago, Ephedrin said:

After reaching cruise altitude my outboard tanks were in sum equal to the inboard tanks, so I turned off the X feed and the OVRD pumps, as learned. But then the airplane complained about the OVRD pumps being off and I turned them back on. 

There is a quirk I found, don't know if this is correct but since I mentioned it during beta and it didn't change I presume it is correct:  Do not configure TANK/ENG until you see the TANK/ENG message on the EICAS.  Doing so before the message will result in the system nagging you to turn the OVRDs back on.  Be patient, wait for her to tell you to make the change and then do it.  There is a lot more complexity going on behind the scenes when changes in deck angle are involved.  The EICAS will guide you.

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2 hours ago, downscc said:

There is a quirk I found, don't know if this is correct but since I mentioned it during beta and it didn't change I presume it is correct:  Do not configure TANK/ENG until you see the TANK/ENG message on the EICAS.  Doing so before the message will result in the system nagging you to turn the OVRDs back on.  Be patient, wait for her to tell you to make the change and then do it.  There is a lot more complexity going on behind the scenes when changes in deck angle are involved.  The EICAS will guide you.

Dan,

this could absolutely be spot on... there was about 200kg left to burn until it would have notified me and I set it without being told so. Thanks for that, I will try it out the next time.. 

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