Hi,
As the title suggests, and the below screenshot of the AFM procedure shows, the el. fuel pump off on the rotax powered Da20 should be selected off during preparation for intentional spinning.
Any ideas why?
Less fuel spillage if you don’t recover from the spin? 
Bing carbs were originally designed for gravity flow supply from a motorcycle fuel tank located directly above the carbs, maybe 25 cm of head pressure. I don’t know what pressure regulation is done when they are used with a fuel pump (it would be interesting to know) but in any case I can imagine you don’t want extra pressure overwhelming bouncing float valves during maneuvers, pumping fuel overboard through the overflow hoses. This is especially so given the carbs location directly above the hot exhaust pipes.
Silvaire wrote:
it would be interesting to know
It depends on the aircraft. Some have a return line, some don’t. Other than that I don’t know the details except for the iS which is a straight forward high pressure FI system (and you certainly don’t want to turn off the electrical pump on that engine 
)
I guess you are right. Keeping the electrical fuel pump on could vent fuel all over the place due to bouncing float valves.
I imagine one advantage of the circulating system with a return line is that you can fine tune pressure at the carbs with a flow restriction. That would minimize overfilling of the float bowls during any short period in which the float valve is unseated due to inertial loading.
I guess because you have throttle at IDLE when spinning?
I expect full pump to be ON and fuel switch to aeros/full tanks
(At least what you would do in a T34)
@Peter an eco friendly crash precaution, oh how forward thinking the diamond ac were!
Sving and Silvair, I guess that makes sense.
Coincidentally I have a problem with the main fuel pump on the da20.
On the da20 (a1 models, both 80 and 100 hp versions), and i have flown 4 different ones, after selecting the electric fuel pump off I would get a fuel pressure warning (no fuel pressure gauge installed,just a warning),which lasts anywhere from 3 to 7 seconds.
Once it was particularly nasty, as i selected the electric fuel pump off at 400 feet after departure, the engine started to die on me (not a nice thing to see that low), luckily quickly switching the el pump on delivered the fuel back to the engine.
Main fuel pump has since been replaced on that engine, as I was told by the mechanics…
And i dont turn off the el fuel pump below 1000ft anymore, just dont trust it.
Apparently diamond are familiar with fuel pressure warning indicator lighting, my maintenance told me.
Out of curiosity, who would you contact at diamond, to ask about the the exact reason for selecting el fuel pump off in pre spin procedure?
Ga90 wrote:
who would you contact at diamond, to ask about the the exact reason for selecting el fuel pump off in pre spin procedure?
The test pilot Some report must exist somewhere, but if anyone at Diamond will bother to look for it, I don’t know.
Same procedure with the Grob 115 C. 
Later the POH says the reason is a potential risk of fire due to flooding of the carburetor:
