I reviewed the first 50 NTSB accident reports involving
water-contaminated fuel, as delivered by their online query routine
("water NEAR fuel").
The reports that have enough detail suggest that the most common cause
of the contamination is fuel entering the tank(s) from rainwater
entering the fuel filler. E.g., several inches of recent rain
showers,
and filler cap seals deteriorated. They cite also inadequate design,
where the tank drains do not evacuate from the very bottom of the
tank. Thus water collects in the bottom of the tank from either/both
entry via the fuel filler or condensate, over time. Especially in
those A/C where the pilot drains clean samples in preflight, while the
A/C sits nose-high, but "bingo," later in reaching level flight, water
begins flowing in enough quantity to cause engine stoppage. E.g., in
several of the above reports, "Pilot told investigators that some
water was found the fuel sample, but he continued sampling until
clear." Yet large quantities of water in the tank (and gascolator)
would be found at the accident site.
I have read elsewhere that the amount of water from condensate in even
an empty tank is too little to cause a big problem by itself in a
single cycle. The problem comes in many condensation cycles over
time, in the scenario above. Once water from humid air in a tank
condenses and makes its way down to the bottom, the air in the tank is
too dry for much more on the next cooling cycle. I doubt the tank
vent can exchange dry air for any significant amount of humid air
outside. But in 25 years of tank/sump draining on my AA-5, I have
never
sampled a drop of water. But water intake on AA-5's is a problem per
NTSB, if a cap seal is bad and the scupper drain is clogged (I do my
own annuals, as shops can miss this stuff!).
The design question seems to be whether one should be able to drain
the Europa tank, in addition to any gascolator installed. The
Europa-designed tank drains accomplish this. If you start sucking
water, once a downstream gascolator fills with water, it can't trap
any more. I'm not sure of all this, just tossing out for comment.
But the NTSB reports were eye-opening for me on this issue.
One advantage of a gascolator, in my meager understanding of all this,
is that fuel delivered with water in a fillup just prior to flight
takes so long to settle that an immediate fuel sample is useless. So
it becomes the "last line of defense." But note, though, in the above
sample reports, the FBO's fuel tested negative, where such testing was
cited.
Regards,
Fred F., A063, N3EU
Fergus Kyle wrote:
>
> Cheers,
> I know this isn't very bright, but I just concluded that it might
> intrigue further discussion. here in La-la-land North, we are4 required
> to install a gascolator at the lowest point in the fuel system. I've
> been pushing testers into the bottom of these things sinec 1952, and
> they've saved my bacon on several occasions. I have the opinion that
> they surely entrap foreign material however they are situate in the
> system, but the real value is in sourcing water enroute the carb.
> Now, am I right that nearly all this water is the result of
> condensation (mostly tankside) somewhere along the way (we cache fuel in
> the North and used to use felt hat crowns to filter it from the
> barrels). If that's so, then nearly all the water settles when the a/c
> is stored (ie: tail up on the trailer. If THAT is so, then the
> gascolator may be sited for its lowest point WHEN fuselage is horizontal
> (stored or flying).
> As this gives me greaqter scope, would be appreciative of any
> cautionary remarks thereto........
> Happy Landings
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