Auxiliary Fuel Pump Mystery

[skymstr02]

There may have been an air bubble in the line preventing the pump from working. This is called cavitation. The pumps will not pump air. Was the fuel selector turned OFF after the previous flight?

Basically, I would chalk this up to loss of prime on the pump.

[jchronic]

Ernie-
I concur re pump cavitation. Not quite the same critical situation, but I once had the same type of occurrence with the auxiliary engine on my sailboat with a slug of air trapped between the primary fuel filter/lift pump (analogous to the airplane aux pump) and the engine-driven fuel pump. Bleeding the system a couple of times cured it.

That said, I'd fly the airplane locally an hour or so before taking off for the islands.

Ahab

[Ernie Martin]

Thanks to both. I think you're right.

Ernie

[hharney]

Ernie
Just out of curiosity did you move the fuel selectors at anytime during this incident? I think someone asked that above but you didn't mention anything about the selectors.

[Ernie Martin]

Yes. No one asked, but I mentioned it in my report, that I had cross-fed, but it still didn't pump.

Ernie

[Roger]

I vote for vapor/air lock. Keep in mind that the pumps will sound different if they have liqiud running through them, vs just air, which may be what sounded confusing to the mechanic.

[hharney]

Originally Posted by Ernie Martin

Yes. No one asked, but I mentioned it in my report, that I had cross-fed, but it still didn't pump.

Ernie

If you look at Skymaster O2 post he was asking if you happened to turn them off. When the selectors are off or in AUX the pump is not fed. Of course your vintage doesn't have AUX, right?

[Ernie Martin]

Sorry, I missed that question. But, no, the selectors were not turned to OFF after the previous flight. I checked that, and I also checked that there was fuel in the tank by cross-feeding the other engine and running that engine's aux pump until I saw fuel dripping from that engine.

Ernie