External fuel tanks warning light.

[TBear]

Hallo all.
I'm having trouble in understanding how the external fuel warning lights work.

If I understood good from the manual, there is no gauge that indicates the external tanks fuel quantity. You can realize they are empty when the green warning lights on the telelight panel are on. They are on because not because the tanks are empty, but because the pumps are not working and this usually happens because the tanks are empty.

But my problem is that those lights are always on as soon as i take off and they never go off. Of course the External tanks knob is set on (switched towards the external tanks). It doesn't seem to be normal and i really cant understand if my plane is using them or not. 
What I'm doing wrong?

Thanks in advance for any kind of help

[Jel]

I think you want to understand how fuel flow is directed in the Phantom. It´s a bit different from what one might be used to

 

The external tanks warning lights are ON when there is NO fuel flow from those tanks into your internal tanks.

That might be 

a) because they are empty or

b) because your internals are still full (above 10500 total iirc)

In both cases you will see the green lights on. They should go blank when your externals start flow again to refill your internal total, then illuminate again when flow stops. This repeats several times until your externals are empty.

 

You can´t really "see" if your bags are empty. You CAN however tell by looking at your total fuel. The totalizer shows your INTERNAL total fuel - that is internal main + internal wing tanks. If the totalizer drops below 10 and your external tank lights are still ON, those externals are most likely empty.

If they are, be sure to reset your external tank feed switch back to the middle position, otherwise your fuel in your internal wing tanks won´t get transferred to your main tanks and the totalizer will show more than you actually got available.

Edited May 26, 2024 by Jel

[Amarok_73]

Good old RTFM is still in use... ;-D
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[Nealius]

Manual doesn't explain why left/right fuel lights would be on when NOT carrying wing tanks, and fuel switch set to internal fuel.

[LizardKingYB]

1 hour ago, Nealius said:

Manual doesn't explain why left/right fuel lights would be on when NOT carrying wing tanks, and fuel switch set to internal fuel.

I also saw a few times all 3 lamps in time when I had on my plane or center tank or wings.

[TBear]

Well...the manuale wasn't so clear at the first clance, but now i fugured It out...

I didn't notice the fuel gauge rising and lowering the values. So, When the external fuel tank Is feeding the internal tank, You can see the gauge values rising and the ext tank warning light off. When the internal tank Is full the the ext tank pump stops feeding and the warning light Is on. 

When the ext tank Is empty, the fuel gauge values keeps lowering (and goes under 11000 pounds). At this point You can jettison the ext thanks.

[Zabuzard]

On 5/27/2024 at 2:25 AM, Nealius said:

Manual doesn't explain why left/right fuel lights would be on when NOT carrying wing tanks, and fuel switch set to internal fuel.

Please make sure to also read the paragraph below the snippet posted above, thanks: