AIUI: The supply system has microfilters that are checked daily (or more often) for crud and for water. As does the truck or pumping device.
I’m not aware of any checks of aircraft fuel sumps done by our maintenance folks. AFAIK if it happens at all, it’ll happen at the bigger disassembly checks that happen every few months or years.
For airline type jets that get a lot of use each day, we’re not greatly concerned about condensation forming in the tanks. The bigger concern is some kind of leak that lets groundwater get into the fuel storage tanks or supply plumbing. Biz jets or genav pistons that get flown once a month (if that) have different concerns.
Another difference is that we always fuel using only single-point pressure fueling systems, so no one is opening a fill port on top of the wing and having rain or snow possibly falling in. As well, we’re normally fuelling from an in-ground hydrant system, not a tanker truck. So the focus is on keeping the fuel clean throughout the hydrant systems. A tanker truck that could sit out in the rain and take on a few gallons of water is only rarely in the picture.
@JHBoom: Being formerly in the tanker biz and now in the A&P biz, care to add anything to the side discussion above about water in jet fuel and the countermeasures in place to prevent it?
Jet fuel always has a small amount of water in it. Always. It’s the nature of the stuff.
Countermeasures include minimizing or eliminating exposure of the fuel to the atmosphere, draining fuel tank sumps when an aircraft has sat idle for long periods, and filtration/separation equipment installed in fuel distribution systems (to include the fuel trucks themselves).
Thanks for the input. I know the big boys do things different than helis. I think the rounding error in a jumbo’s fuel capacity is more than we carry total.
The case I was referring (apple jelly) came from contaminated storage tanks, but it made a holy mess in the cells. Lucky they never had a flameout.
Even so, the operators never sumped their cells. An accumulated water slug can cause a flamout, if you were unlucky and it went all at once.
Water and jet fuel don’t mix, but they mix better than water and gasoline. With the effect that water in a gasoline tank tends to settle out pretty quickly into a blob at the bottom, whereas it takes much longer for the same amount of water in the same amount of jet fuel to do the same thing.
As long as the water is finely suspended throughout the fuel and isn’t too high a percentage, the pumps, lines, and engines process it just fine. Here’s info about additives blended into fuel to enhance that suspension effect and delay the water separation into macroscopic drops. Fuel system icing inhibitor - Wikipedia
If we posit that somehow a bunch of water got into a big jet fuel tank and had time to settle out into the low sumps where the fuel pump pickups sit, I’d expect we’d discover that during start or taxi. We normally get through 200-300 lbs ~= 50 gallons per engine before takeoff. Which is far more fuel than sits in the plumbing between tank & engine.
I recall an AD on a genav airplane that had rubber bladders for the fuel cells. Apparently it was difficult bordering on impossible to install the bladders properly so the bottoms were totally flat in the wing bays. Which led to the bladders having a rippled bottom surface with multiple low spots. Only one of which was the sump where the preflight drain and fuel line pickup were.
Sure enough, water would collect in all the low spots, not just the one the engineers intended. And once airborne doing a little maneuvering the multiple slugs of water would migrate to the true sump and be fed to the engine resulting in unexpected silence. I *hate *it when that happens.
Jets generally don’t use bladders; the wing structure bays *are *the tankage using some interior sealant to make the panel joints fuel tight.