Newbie Question 2 - Fuel Exhaustion if <15 Gals?

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nworthin
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Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by nworthin »

The procedures call for use of the transfer pumps when mains hold 15 gallons each (or 17 if over water).

As explained by my transition trainer this is because the transfer pumps can not keep up with fuel burn (at least in some power settings). Is this the case?

This seems like an incredibly poor design especially since there's no CAS warning about low main fuel levels (until very low).

If this really is the design, what's the SOP most folks follow? Just turn the transfer pumps on as soon as at a safe altitude since you can't over transfer?

This one is really perplexing....
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by CFIDave »

Fuel transfer pumps each operate about 1 gal/minute. So they easily keep up with fuel burn.
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Gordon
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by Gordon »

Agree, I normally cruise at 75% - when you start transferring the fuel quantity in the mains goes up - actually all the way to full so I often have to do more than one transfer. I have an early 62 without AUX tank gauges so I like to transfer earlier (17 gal) rather than later so I can see my fuel on the gauges! There is the fuel used function to give me burn from take off - but I still like to see it on the gauges.
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nworthin
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by nworthin »

CFIDave wrote: Thu Jul 07, 2022 3:12 am Fuel transfer pumps each operate about 1 gal/minute. So they easily keep up with fuel burn.
So, what's the rationale to start transferring at 15 gallons then?

Trying to understand what's behind the procedure...
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by CFIDave »

You want to know that you can transfer the fuel to the mains before you need it -- especially when flying long legs over water.

(I actually had one pump fail in flight on my DA42-VI, but fortunately I was still able to get to my destination without accessing all the fuel in the AUX tanks.)
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by Colin »

I always start pumping at ten gallons.
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nworthin
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by nworthin »

CFIDave wrote: Thu Jul 07, 2022 4:48 am You want to know that you can transfer the fuel to the mains before you need it -- especially when flying long legs over water.

(I actually had one pump fail in flight on my DA42-VI, but fortunately I was still able to get to my destination without accessing all the fuel in the AUX tanks.)
Ok, it's prudence...

So, let me be a bit cranky and ask why not just ALWAYS turn on the transfer pumps once reaching a safe altitude?
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by Chris »

nworthin wrote: Thu Jul 07, 2022 6:01 pm So, let me be a bit cranky and ask why not just ALWAYS turn on the transfer pumps once reaching a safe altitude?
Well I suppose if the auto-shutoff-on-full feature fails then I guess you would be pumping more fuel out the vents. But assuming things are working properly I don't know of a good reason.

I try to turn on the aux pumps in my DA42 when my mains read between 13-15 gallons and turn them off when it reads 20 or so. This avoids the "dead zone" between 17-19 when the fuel guages don't register any changes for a while due to fuel probe design. I.e. I can quickly tell that the pumps are working when it starts to increment and then I turn it off when it starts incrementing again above the dead zone. That way I have a good read on how much fuel was transfered (and how much should be left in the aux tanks).
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Re: Newbie Question 2 - Fuel Exhaustion if <15 Gals?

Post by photoSteveZ »

My first DA62 had an intermittent faulty sensor and the L Aux tank pump would sometimes fail to turn off before the main tank was full. We pumped a little Jet-A overboard from time to time as a result. You can see fuel mist streaming off the trailing edge of the wing when it happens.

I’ve got a recurring 90 minute “CHECK AUX TANKS” alert programmed into the G1000, but depending on the mission profile and my fuel state I sometimes start the Aux pumps as soon as I finish the after-takeoff checks.
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