Stupid question: water in fuel

paul kgyy wrote:
You can use a GATS jar for checking your fuel. It has a screen that
removes water when you pour back into the tank.

My guess is that water separator are rather new, and the volume doesn't
justify anyone producing a certified unit for aircraft?


Not new at all. They've been used on diesel engines for at least 25
years. I had a water trapping filter on my fuel pump tank when I owned
a 182 and ran auto gas in it. I definitely didn't want to be adding
water to the tanks beyond what they might collect naturally, although, I
never found water in the fuel in 6 years of flying. However, I was
always expecting it given that the 67 had fuel bladders which were known
for having wrinkles that could trap large amounts of water and let it
loose at inopportune times. My partner and I always did a vigorous wing
rock before draining the sumps, however, we never found anything. We
did have the flush fuel cap upgrade which was supposed to greatly reduce
the change of water ingestion.

I'm not sure why they aren't used on airplanes, other than they add
cost, weight, and another item to get certified. Also, although I never
saw the problem on the diesels I used to operate, it may be that the
filter has a nasty failure mode if it collects enough water. For
example, maybe they clog completely. I don't know, just wondering if
there isn't some downside like that which obviates the benefit for
airplane use.

Matt