Jump to content

Fuel Tank balancing (in-flight)


softreset
 Share

Recommended Posts

Reference material - https://www.smartcockpit.com/docs/CL605-FUEL_SYSTEM.pdf

Page: 16

Fuel tanks are expected to be within 400 lbs / 181 kgs of each other on taxi / takeoff / landing OR 800 lbs / 362 kgs during flight, to avoid Fuel Imbalance EICAS message.

  • First, orient yourself on the overhead panel, we'll be working in the 2nd row (or middle row) of the FUEL panel area. (Fuel.PNG)
  • All three of these buttons should be extinguished under normal operations.

Gravity XFLOW

Press to begin the process, there's a 1 second delay after pushing the button for it to illuminate OPEN. This will allow fuel to flow freely between both main (wing-based) tanks. There is no EICAS notification that this is open/occurring. (gravity.png)

To observe what's happening in the sim. You can go to the Challenger 650 menu -> Study -> Engines -> Fuel System...

You'll notice that whatever Main Tank (either Left or Right) has more fuel that this will continue to consume, whereas the side with less fuel will not. Thus balancing the tanks.

L (R) to AUX XFLOW

Press the appropriate button to begin the process, there's a 1 second delay after pushing the button for it to illuminate ON. This will remove fuel from whatever side is select and transfer it to the auxiliary tank.

  • Determine which tank has more weight in fuel
  • Left side? Choose L to AUX (L to AUX.png)
  • Right side? Choose R to AUX (R to AUX.png)

There is a lock out mechanism that does not allow you to press the opposite button when one is already selected. Pressing L to AUX, for example, then pressing R to AUX, will no longer illuminate the L to AUX button. Pressing the R to AUX button again will resume the L to AUX transfer and the button will illuminate ON again.

Once you're done balancing the tank, make sure to deselect the previously selected L (R) to AUX button. The aircraft will now suspend fuel consumption from the two main tanks and pull from the AUX tank until depleted.

*Edit* Thanks! @airforce2
As long as a main tank is below 93% full, the aux tank feeds the main tank to maintain the level at 93%.  Once a main drops to 93%, the main quantity will remain constant and the aux level will drop.  It will appear that the engines are burning from the aux tank, but in reality the engines are burning from the mains and that fuel is being simultaneously replaced in the main tank from the aux tank ejector xfer pumps.

To observe what's happening in the sim. You can go to the Challenger 650 menu -> Study -> Engines -> Fuel System...

Note: The plane will display an EICAS warning message: FUEL XFLOW SOV OPEN if either button is ON for more than 50 seconds and the tanks are balanced within 100 lbs.

 

Fuel.PNG

gravity.PNG

R to AUX.PNG

L to AUX.PNG

Edited by softreset
  • Like 16
  • Upvote 4
Link to comment
Share on other sites

  • Pils pinned this topic
On 1/13/2022 at 1:55 AM, Ed Moore said:

Just to add to this I highly recommend setting a timer on your phone or something if you start a transfer to aux - multiple times I have ended up with an imbalance the other way because I forgot it was running.

We use a flip down FLOW sign to remind us, a audio warning as you suggested is a great idea 

Link to comment
Share on other sites

On 1/13/2022 at 10:55 AM, Ed Moore said:

Just to add to this I highly recommend setting a timer on your phone or something if you start a transfer to aux - multiple times I have ended up with an imbalance the other way because I forgot it was running.

As @softreset already point out with his last note as long the tanks are almost balanced you get on EICAS a warning (with audio alert) FUEL XFLOW SOV OPEN to remind you to close L(R) 2AUX FLOW.

Link to comment
Share on other sites

  • 2 months later...
On 1/8/2022 at 9:48 PM, softreset said:

Once you're done balancing the tank, make sure to deselect the previously selected L (R) to AUX button. The aircraft will now suspend fuel consumption from the two main tanks and pull from the AUX tank until depleted.

As I understand it, the engines never suspend consumption from the mains--they feed *only* from the main tanks, never directly from the aux tanks.  Though the collector tanks are physically located in the aux tank, they remain functional components of the main tank system, in that they only receive fuel from the mains. 

As long as a main tank is below 93% full, the aux tank feeds the main tank to maintain the level at 93%.  Once a main drops to 93%, the main quantity will remain constant and the aux level will drop.  It will appear that the engines are burning from the aux tank, but in reality the engines are burning from the mains and that fuel is being simultaneously replaced in the main tank from the aux tank ejector xfer pumps.

Regards

Bob

Edited by airforce2
  • Like 3
Link to comment
Share on other sites

2 hours ago, airforce2 said:

As I understand it, the engines never suspend consumption from the mains--they feed *only* from the main tanks, never directly from the aux tanks.  Though the collector tanks are physically located in the aux tank, they remain functional components of the main tank system, in that they only receive fuel from the mains. 

Correct

image.thumb.png.d880030d8a5c824eb25db89da0267cc1.png

Link to comment
Share on other sites

On 3/30/2022 at 10:53 AM, airforce2 said:

As I understand it, the engines never suspend consumption from the mains--they feed *only* from the main tanks, never directly from the aux tanks.  Though the collector tanks are physically located in the aux tank, they remain functional components of the main tank system, in that they only receive fuel from the mains. 

Thanks Bob, you're absolutely right. I've edited my original post to reflect that.

  • Like 1
Link to comment
Share on other sites

  • 4 months later...

The above reference helped me understand why I develop an imbalance on the ground.  The APU's fuel source is from the right main tank, and that is indeed the one that goes lower when I am sitting in the plane continuing to learn its systems after I have started the engines.  If I had to pay for the gas and maintenance then this would be self correcting!

 

  • Like 2
Link to comment
Share on other sites

  • 1 month later...
On 1/13/2022 at 2:55 AM, Ed Moore said:

Just to add to this I highly recommend setting a timer on your phone or something if you start a transfer to aux - multiple times I have ended up with an imbalance the other way because I forgot it was running.

Used to put a checklist between the throttles so as to not forget.

Link to comment
Share on other sites

  • 11 months later...
17 minutes ago, HussamAli said:

Thanks for the procedure clarification to rebalance the tanks. Today I had an imbalance of 800 lbs , and it took me over 25 mins to balance them. Is this normal ? 
If on the ground and the APU is on, can we preemptively prevent an imbalance by turning on the R to Aux button ?

800 lbs is a significant imbalance so I’m not surprised it took a while. “To Aux” isn’t a pump-driven transfer, purely gravity.

Link to comment
Share on other sites

  • 2 weeks later...

In a long conversation with BBA yesterday we learned that BBA advises to equalize left and right mains BEFORE departure using the L (usually) to AUX pumps, even if the difference is lower that the limit of 400 lbs. This in order to avoid CAS fuel imbalance messages after departure which could be triggered by banking and 'sloshing' in the tanks

  • Like 1
Link to comment
Share on other sites

  • 4 months later...

twice now I was on final and suffered flame out on 1 engine left because the fuel was not equal 20 in left 50 I followed the above procedures cross valve opened  so it should have had continuous fuel for both engines or balanced it equal  but nothing moved into that left tank..i don't understand according to the flight plan i should have had enough.

Link to comment
Share on other sites

4 hours ago, simking1 said:

twice now I was on final and suffered flame out on 1 engine left because the fuel was not equal 20 in left 50 I followed the above procedures cross valve opened  so it should have had continuous fuel for both engines or balanced it equal  but nothing moved into that left tank..i don't understand according to the flight plan i should have had enough.

Once you’re down to those levels the sensors are unreliable and not all fuel in the tanks is even usable. You should be planning to land with 4,000 lbs, obviously something went rather wrong in your fuel planning. :)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...