DA40 Fuel Pump Operation

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thefoxx
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Re: DA40 Fuel Pump Operation

Post by thefoxx »

Great insight Dave - this is varying from the topic slightly, but is the principle the same in our DA20's with the Continental IO-240B? I was questioning that the fuel pump may not have enough pressure (according to the fuel pressure gauge) to keep the engine running if the engine driven pump fails - although on prime, it boosts the pressure pretty close.

Thanks!
CFIDave wrote:The fuel systems of Continental (e.g., Cirrus SR22, older SR20s, or Beech Bo/Baron) vs. Lycoming are designed very differently, so it's not surprising that different procedures are used for run-up, takeoff/landing, starting, etc.

On Lycoming DA40s the system is quite simple with the electric pump in-line/in series with the engine's mechanical pump, to provide multiple uses:
- To prime the engine for cold starts,
- To provide additional pressure at higher altitudes (e.g., greater than 10,000 feet),
- To act as a backup in case the mechanical pump should fail during critical phases of flight (e.g, takeoff and landing),
- To maintain fuel pressure when switching between L and R tanks (although this is no longer common practice among many DA40 owners attempting to minimize fuel pump use; to my knowledge there's never been an engine stoppage caused by not using the pump during fuel tank switching).
On a Lycoming, the electric fuel pump is "supplementary" to the engine's mechanical pump.

The fuel system on Diamond JetA diesels is a much more complex design with re-circulation of unused fuel from the common rail back into the tank, parallel electric pumps in case one fails, a bypass valve around the electric pumps' fuel filters in case they get clogged, etc. -- not at all like the simpler Lycoming fuel system. An electric fuel pump AND the engine's mechanical high pressure fuel pump for the common fuel rail must both be running all the time; unless at least one of the parallel electric fuel pumps is operating, the engine will quit.
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Re: DA40 Fuel Pump Operation

Post by CFIDave »

TimS wrote: And based on your posting, I would think following the AFM and having the fuel pump on during run up makes sense.
Diamond's DA40 checklist for the Lycoming DA40 has the electric fuel pump OFF during the run-up.

Why? If you were having any issues with the engine's mechanical fuel pump, it would be good to experience poor engine performance on the ground during the run-up, not masked by the assist of an electric fuel pump turned ON.
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Re: DA40 Fuel Pump Operation

Post by TimS »

CFIDave wrote:
TimS wrote: And based on your posting, I would think following the AFM and having the fuel pump on during run up makes sense.
Diamond's DA40 checklist for the Lycoming DA40 has the electric fuel pump OFF during the run-up.

Why? If you were having any issues with the engine's mechanical fuel pump, it would be good to experience poor engine performance on the ground during the run-up, not masked by the assist of an electric fuel pump turned ON.
The OP stated Diamond specifies the pump be on. :?:

Tim
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Re: DA40 Fuel Pump Operation

Post by DiamondMike1 »

Yes, Diamond AFM p. 4A-23 specifies Electric Fuel Pump on during run-up.
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Re: DA40 Fuel Pump Operation

Post by CFIDave »

The 2014 AFM does indeed specify electric fuel pump ON during the run-up.

But Diamond's newer 2015 checklist shows it turned OFF during the run-up (see page 5):
http://support.diamond-air.at/cl_da40-1 ... 73ab0.html

So there's a contradiction...

I instruct students and new owners to use Diamond's checklist when doing run-ups in the airplane, not a big 3-ring binder AFM.
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Re: DA40 Fuel Pump Operation

Post by Rich »

With respect to having the FP on during runup: What exactly does it prove about one or both of the pumps?

Answer: Not much. - just that one or the other or both pumps together is capable of producing maybe 50% power. You don't know which of the three possibilities is accurate.

And then what? Leave it on until after takeoff? Anyone else ever wind up holding for 10 minutes or more waiting for IFR release or traffic jams?

Basically, I consider the runup to be a preliminary "runup". The more important one occurs from the start of the takeoff roll to go/no-go decision around rotation time:

- RPM as expected?
- MAP as expected?
- EGTs as expected?
- Engine sound and feel normal"?
- Acceleration as expected?
- The plane overall feel normal?
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DiamondMike1

Re: DA40 Fuel Pump Operation

Post by DiamondMike1 »

Thanks Dave.

Reference to that checklist is exactly what I was looking for to support my idea of having the electric fuel pump OFF for run up, which is what I will continue to do.

Mike
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Re: DA40 Fuel Pump Operation

Post by Rich »

OK, now that conforming to the check list vis-a-vis the fuel pump running or not is settled, how many folks really adhere to the entire pre-takeoff checklist? I specifically refer to the AP items as an example. ;)
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Re: DA40 Fuel Pump Operation

Post by gordsh »

I do but I am a student pilot at this time...I have not yet had a chance to develop some "skip over that" habits ;)
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Re: DA40 Fuel Pump Operation

Post by Colin »

John Deakin taught me that some of the things the manufacturer wants you to do are bad for your plane. His example was that pulling the prop control three times was pointless and potentially harmful, so he only did that after maintenance or after the engine had sat for more than a week. I read a whole column on his reasoning and I believe him. In my DA40 there were a couple things like that which I skipped.

I put a red ring on the circuit breaker for the autopilot. I have tried manually overpowering it and I can do it, but I wouldn't try. If the red button on my stick didn't work that red collar is getting pulled very very quickly.

Free and correct? EVERY TIME. I'm not sure HOW the ailerons could get cross wired while my plane has sat quietly at lunch, but I still check it. And when I lean the stick over and check I hear my friend Susan say, "Up yours," which was her verbal check that the correct one popped up.

Most things on that checklist, every single time I start the engines. I totally understand the checklist keep us from having more accidents. Follow checklist: it all gets done. Don't follow checklist: you run your Gulfstream off the end of the runway with the control lock in place. Seems impossible when you are first learning, then you read all the NTSB reports (which I do), and it is clearly possible.
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