DA40NG transfer pump acting strange

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manatee
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DA40NG transfer pump acting strange

Post by manatee »

Hello all - I recently bought a 2020 DA40NG (delivered in April of this year). It's been going well; I really love the plane and already have about 40 hours on the tach from all the flying. I browsed this forum quite a bit before buying and will post more as an owner.

This past weekend I had the fuel topped off in both tanks and went on a flight. After about 5 gallons of fuel burn into the flight, I pressed the button to turn on the transfer pump. The annunciator began flickering on and off; I could not tell if the fuel pump was working in flight by sound (my girlfriend said she could hear it but my hearing is not quite as good). It also did not appear to be transferring anything based on the fuel gauges. I tried a few things such as popping the breaker in and out, turning the pump off and back on, etc. In straight and level flight it was mostly not annunciating and occasionally annunciated briefly while the switch was left on. Banking to the left made it consistently annunciate more often; pitch changes and banking to the right did not seem to have an effect; nor did playing with the rudders. I did not really want to try turning the engine and master switch off and back on again in flight.

I was concerned about having a weight imbalance as the flight continued so I wiggled back and forth with small banks for a while to see if the more frequent annunciations were actually matching transfer pump activity; after a while the fuel in the left tank went up a gallon so the pump was working, just extremely slowly. It could at least pump enough to match the fuel burn at 75% cruise which was nice. On the ground I could not hear any noise from the pump when I turned it on.

I topped off again (really just to dodge the landing fee at Signature...) and on the way home in almost the exact same conditions I tried the pump and it seemed to be working fine, annunciations and all. Overall it was a very odd experience and not sure what to make of it. I sump the tanks on each fill up but I wonder if something was in the fuel and cleared itself up. Any thoughts?
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chili4way
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Re: DA40NG transfer pump acting strange

Post by chili4way »

It sounds like everything is working properly.

In a DA40NG, the fuel transfer pump won't operate until there are less than ~13 gallons indicated in the left tank (e.g. on the G1000 engine page). That means if I start with full tanks (19.5 useable in each wing), I have to burn more than 6.5 gallons before the transfer pump will start to function. The transfer pump turns itself off (and the PFD annunciation starts to become intermittent) as the left tank approaches ~13 gallons. This is when I turn off the transfer switch so as not to abuse the transfer pump with an on-off-on-off operation.

In practice, I set a time for 50 minutes when cleared for takeoff to avoid reaching a 9-gallon fuel imbalance and then reset the time after completing the fuel transfer. Boatguy (Russ) has developed a handy table he uses for scheduling his fuel transfers.
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Re: DA40NG transfer pump acting strange

Post by Boatguy »

Here is the table that Paul referenced. I can send you the underlying Excel workbook if you want to further customize it for yourself.
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Fuel Transfer.pdf
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Re: DA40NG transfer pump acting strange

Post by deeohgee »

Afternoon, thanks for this great post on the fuel transfer pump. This was an issue I experienced yesterday so was amazing to read through the logic of it. The question to me is... do you just turn on the pump and leave it on and let it do its thing or do you monitor the fuel and turn it on and off as needed? The POH isn't clear and based on how it works, it looks like you could just leave it on? At this point, I have been turning it on and off as needed to balance the tanks.
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Re: DA40NG transfer pump acting strange

Post by Donkadillapig »

The way I use it (in cruise) is I set a timer for 3-4 minutes and switch the pump on. Once tanks are balanced I switch it off. It's easy to forget without the timer, which can result in the left winging loading up out of balance. Nothing you can do about that then except burn fuel.
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Re: DA40NG transfer pump acting strange

Post by Boatguy »

deeohgee wrote: Thu Jul 15, 2021 6:13 pm Afternoon, thanks for this great post on the fuel transfer pump. This was an issue I experienced yesterday so was amazing to read through the logic of it. The question to me is... do you just turn on the pump and leave it on and let it do its thing or do you monitor the fuel and turn it on and off as needed? The POH isn't clear and based on how it works, it looks like you could just leave it on? At this point, I have been turning it on and off as needed to balance the tanks.
You don't want to turn on the pump and leave it on as this creates a lot of wear on the pump, the constant flashing of the alert on the PFD, and will ultimately lead to a the difference in the tanks exceeding the 9 gallon limit specified in the AFM.

I set the G1000 timer per the previously posted PDF. When departing with less than full tanks, prior to departure I do a little quick mental math and either level up the tanks, or for short flights transfer an amount so that my expected burn for the flight will result in close to level tanks on landing. That said, any difference up to 9gal is not an issue. The G1000 will issue a "low fuel" warning if you entirely forget to transfer, and you may also experience that warning when there is less than about 5gal in the left tank and you make a right turn while taxiing that briefly sends the fuel away from the sensor.

In practice, I also set the timer for about 30min before arrival and adjust the levels so that my expected burn for the remaining flight will leave me with roughly equal tanks, or at least 5gal in the left tank, so that I don't have to think about fuel during the last 30min before landing or during a "missed" approach. Also, when I do end up transferring "all" the fuel to the left tank, for example when planning to land with 6-7gal (45-60min reserve), I leave 1-2 gal in the right tank to avoid getting a red EMPTY on the MFD for the right tank.
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Re: DA40NG transfer pump acting strange

Post by Lin »

chili4way wrote: Tue Jun 29, 2021 6:15 pm It sounds like everything is working properly.

In a DA40NG, the fuel transfer pump won't operate until there are less than ~13 gallons indicated in the left tank (e.g. on the G1000 engine page). That means if I start with full tanks (19.5 useable in each wing), I have to burn more than 6.5 gallons before the transfer pump will start to function. The transfer pump turns itself off (and the PFD annunciation starts to become intermittent) as the left tank approaches ~13 gallons. This is when I turn off the transfer switch so as not to abuse the transfer pump with an on-off-on-off operation.

In practice, I set a time for 50 minutes when cleared for takeoff to avoid reaching a 9-gallon fuel imbalance and then reset the time after completing the fuel transfer. Boatguy (Russ) has developed a handy table he uses for scheduling his fuel transfers.
Sir,could you tell me where is the “13 us gal ” from?The only thing I got that affect transfer pump from ADM and AMM is high fuel sensor in main tank and low fuel sensor in auxiliary tank.But the publications do not show the actual fuel quantity that the high fuel sensor stand for.Thanks! :D
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Re: DA40NG transfer pump acting strange

Post by chili4way »

I have extended range tanks with two cells in each wing, the inner and the outer. The fuel transfer pump automatically shuts off when the left inner is full. That's when the "high fuel sensor" is activated. After this has happened, my G1000 left tank fuel level reads 13 gallons, even though the usable fuel for the tank is 14 gallons per page 2-28.

The "CAUTION" on Page 2-28 suggests 13 gallons is the "correct" answer, at least for airplanes with extended-range tanks. "If an indicator shows 14 US gal, then 19.5 US gal must be assumed for the calculation of the difference between right and left tank." The 13-gallon reading makes it clear that the outer tank cell (which has no fuel level sensors) is empty. So if you're looking for an AFM reference, this is probably a good one.
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