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How can water get into the tanks?

Before departing Dresden yesterday I drained the fuel and it was clean.
Today I got a photo from the pilot that flew after me:

I flew through the rain for about 30 minutes.

The fuel system is supposed to be a closed system.
How can water get into the tanks?

The fuel system is supposed to be a closed system.
How can water get into the tanks?

Obviously it isn’t. What exactly do you mean by closed?

The fuel system is supposed to be a closed system.

There are vents, the used fuel is replaced by outside air. That contains water vapour which can end up as water in the fuel. When the quantity is large, it’s usually the filler cap.

Condensation while parked is the main cause, I always learned. Which is one more reason for filling up immediately after landing.

EBZH Kiewit, Belgium

I’d say it’s the filler caps that don’t seal well.

Condensation while parked is the main cause, I always learned.

I was taught that too. But I don’t believe it.

Having flown aircraft for years without ever seeing water in the fuel, and living and flying in a country known for its damp air, I just don’t believe it. Some aircraft never have water in the fuel. Occasionally you find an aircraft that always has it.

I only see four possibilities:

1. Dodgy filler caps, and either Lenthamen flew through rain, or it rained when on the ground
2. It was present there all a long and Lenthamen missed it during the preflight. Perhaps due to the way it was parked/not level, or perhaps the aircraft has bladder tanks and it was caught in a fold?
3. It was added when the next pilot was refuelling.
4. Someone deliberately added it afterwards.

Anything coming from condensation will be very minor.

Are you sure it’s water? It has a very strange brown colour, and I don’t see any fuel above it. Any possibility it’s a different fuel type that was added?

Last Edited by dublinpilot at 26 May 19:34
EIWT Weston

There was about 2cc water drained from the tanks.
It must have been picked up during the 3 hours flight with lots of IMC and rain yesterday.
I used about 80L of fuel.

Check the filler cap seals and if in doubt, replace them!

What dublinpilot said. Condensation, in this context, is mostly an OWT.

Frankfurt (EDFZ, EDFE), Germany

I would replace the filler cap seals.

Condensation, anywhere on the earth, has a very limited capability to generate lots of water. There is a very good analysis by a bloke called Julian Scarfe, PhD, which should be possible to find with google, in a usenet (“news”) archive, somewhere in rec.aviation.*

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Shoreham EGKA, United Kingdom
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