This subject has been covered a number of times in the LML in the past - there should be a lot of info in the archives. Regardless, I'll add my two cents worth just for the heck of it.

When I first flew my LNC2, I had two Facet fuel transfer pumps, one for each wing tank to header. Not too long into my first few hours, one pump failed - fortunately, I wasn't very far from home. Had I needed the gas in the other wing I would have just plain SOL! I decided that I needed a bit of redundancy in a system as flight safety critical as fuel.

I re-plumbed my system, bringing both wing tank outlets to a selector R/L valve and then ran the outlet from the valve to the same two Facet pumps in series, then to the header. I don't remember the Facet P/N but I checked that it allowed pump-through when de-energized. In this way, fhould one of the pumps fail again, I still can get the fuel from either wing, merely by switching the valve from left to right. The pumps are wired to to allow Off, Left, Right and Both.

Of course, as such things go, I haven't had a transfer pump failure since the first one but I have lost the boost pump (also Facet - with different fittings) at about 300 hours - so, with two failures so far I'm guessing it'll happen again, sooner or later. I fly a bit more comfortably knowing that I can get all the fuel in my wings to my header, even with a single failure.

I only feed the engine from the header tank, so if the pumps empty a wing and suck air for a short time it doesn't affect the engine operation (unless, of course, I get real stupid and run the header dry).

Cheers,

Dan Schaefer