Ice in fuel tank?

[KembleKid]

I was the first to fly our club TB9 on Saturday morning, so did the usual 'A' check. Sampled all three fuel drains - had a good sniff of each sample - definitely looked and smelled like Avgas, no sign of water contamination.

Uneventful flight, but the instructor who took the aircraft out immediately after me also sampled the fuel, and spent 5 minutes draining water from the RH tank. The a/c hadn't been re-fuelled after my 45 min flight.

As well as feeling that luck was on my side that day, I've been beating myself up trying to figure out how I missed so much water.

The aircraft had been parked out overnight (as usual) with tanks full to the brim. The temperature overnight had dropped to below freezing, but by the time I did my 'A' check all signs of frost on the ground and on the aircraft had gone, but it was still pretty cold.

So - my question is this - is it possible that the water in the tank had frozen overnight and there was a big lump of ice at the bottom of the tank? Could it be that the water was sitting elsewhere and only moved to the drain after I'd sampled?

Any thoughts appreciated, as realising that I'd flown with so much water in a tank was a bit of a shock. How can I make sure this doesn't happen again?

[BackPacker]

Other than ice, which sounds very plausible, does the TB9 by any chance have rubber fuel bladders like Cessna?

These are known to wrinkle and trap water in the wrinkles. Rocking the wings before sampling will at least alert you to the presence of water.

But I'd be interested in a failsafe way of detecting water in freezing conditions in any case.

[SNS3Guppy]

Sure, water freezes in the tanks...part of the reason you need to sump and test the fuel each time you fuel...even when you fuel it up to leave overnight.

Chances are that if the water was coming out after your flight, it wasn't just thawing. Simply walking up to the airplane and sumping the tanks is inadequate. You need to actively rock the wings and in many cases raise and lower the tail. Work that water down to the low points, because up until then, it could be anywhere.

One more good reason to thoroughly warm your airplane before flight.

[hobbit1983]

How long will it take, if I rock the wings, for all the water to settle at the lowest point where it can be drained? i.e. if I rock the wings at the start of the A check, will I be able to get all the water out at the end of it (for example)?

[KembleKid]

I did actually rock the wings at the start of my 'A' check, although the reason for doing so was more to check for failure of the main spar. I was taught to do this by one of my instructors, although personally I would have expected any such major failure to have been pretty obvious, but I still do it.

I guess there would have been a delay of a few minutes after rocking the wings to taking the samples.

[IO540]

Unfortunately you cannot usefully rock the wings of anything much larger than a C150.

I am also not sure whether rocking the wings is a good idea because it might redistribute water that has collected nicely around the drain hole, just as it should.

Ice accumulation is a possibility but it tends to happen in climates where you get constant sub-zero temps; this is very rare in the UK. There have been airliners which were constantly operating in sub-zero and were found to be carrying massive lumps of ice weighing several tons.

[Kolibear]

definately looked and smelled like Avgas,

Neither of which proves that it was Avgas.

Try spitting into the sample, if the spittle sinks, its avgas; if it floats, you have avgas-flavoured water.

The alternative test is to use a lighter.......:uhoh:

[fernytickles]

A C210 I fly had water delivered into the tanks during a fuelling one time. It took the mechanics about 3 weeks of jacking the aeroplane up first on one side then on the other to move the water around sufficiently to finally get rid of all of it. That was quite an eye opener for me. I've experienced large amounts of water draining from a Lance after it sat out all day in the rain, and assumed I'd got all the water after 3 or 4 cups emptied out. I guess every plane and every situation is different.

[KembleKid]

Try spitting into the sample, if the spittle sinks, its avgas


Must admit - that trick hadn't occurred to me, but I'll try anything if there's a chance of improving my life expectancy!

[RatherBeFlying]

How level is the location where the TB9 was parked?

If the parking location has a bit of a slope, then it would not be a surprise if water appeared when it was placed upon a level area.

Yes, water could freeze overnight, but I suspect it would take a significant warming over the freezing point and time to reliquify it.

It's usually colder aloft but inversions are more common in the winter.

[KembleKid]

The TB9 is parked on a perfectly level concrete stand, so I would hope any water would collect at the drain points.

[IO540]

I fly a TB20 and have never heard of any problem whatsoever with water retention, which cannot be simply drained via the three drain points. The TB is a properly designed aircraft without any "funny business".

Have you asked at the Socata TB owners owners group www.socata.org (http://www.socata.org) ?

[Mariner9]

I would hope any water would collect at the drain points.

Not much point in having a drain point anywhere other than the lowest point in the tank. Therefore, if water was present at the drain points, it couldn't have been frozen else you would have been unable to draw a sample at all.

Did you see the water the instructor drew off?

[Fake Sealion]

If there was a layer of frozen water in the tanks, does this mean the temperature of the FUEL drawn off would by definition be very near to or lower than zero certigrade?

If so . . . . if on a cold morning the temp of the drawn fuel is taken with a basic thermometer AND it is at or below zero - BEWARE - ice could be present in the tank?

Comments from someone more scientifically literate most welcome!!:bored:

[snips]

You could get water in the tanks from flying through rain/showers etc with old and perished fuel cap seals.


Cheers Snips

[KembleKid]

Did you see the water the instructor drew off?


No - but my son did, as he was having a lesson immediately after he'd flown with me. The instructor was demonstrating an 'A' check to him - just as I'd done an hour earlier. In fact, I'd made my son smell the sample from the tank in which the water was found by the instructor. I can picture the look on my son's face as he took a lungful of Avgas fumes! I also sniffed the sample, and I'm pretty confident I was't smelling just residual fuel on a tester full of water.

[IO540]

You could get water in the tanks from flying through rain/showers etc with old and perished fuel cap seals.

Basic physics can be used to work out the maximum possible amount of water that could collect in a fuel tank of a given volume. It is suprisingly small - a few cubic cm for most GA types.

IMHO, the vast majority of water found in GA tanks gets in through perished fuel cap seals. So I guess the answer is YES it could happen in flight.

I once drained out five beakers full of water from a trainer - appalling maintenance by a company with an AOC for public transport.

[SNS3Guppy]

You can move the wings around and rock the airplane in all sizes. I do it in the Learjet...and that's a little bigger than a 152. Simply towing the airplane or moving it a little way can help move water to the lowest point. No, you're not worried about splashing the water out of the low point. In fact, you'll find that around the sump opening there's still a place for material to collect that doesn't go down the drain. What you're looking to do is move water from behind baffles and other locations which may trap the water.

You may be aware that a few years ago Cessna moved from a single drain in each wing to multiple drains in each wing. This occured to address water trapped behind baffles, and in tanks with bladders, in wrinkles in the bladders. Cessna has warned about it for years, but surprisingly many instructors today don't teach their students to rock the wings and raise and lower the tail or shake the airplane as part of the preflight.

The largest share of moisture introduced to fuel is through the fueling itself. If you didn't have moisture before and you did after the tanks were filled...guess where it came from? In times past fuel cap leakage has occasionally been problematic, but seldom is this the case. The lions share of fuel contamination comes from what's pumped on board. Entrained water and other contaminants come all too often with the fuel purchase. If you fuel and then go fly, that water will be settling out as you fly, and when you land you may find you have more water on board It didn't just suddenly condense, it didn't filter in there during the course of the flight. It was put there when you filled up.

I've seen gallons and gallons of water turn up in some fuel systems. I sampled a truck I suspected once and got three different colors of fuel out of it from the hose, from the top of the fuel in the tanks, and from half way into tanks (mid depth), as well as water, leaves, and a dead mouse. I found the differential pressure was too high on the filter, indicating a blocked filter, and no record of routine sampling. I found nearly eight inches of rust in the bottom of the tanks. I condemned the load, and ultimately cost the fixed based operator about ten thousand gallons of fuel. Unfortunately, not before he sold a load to a transint light airplane that got away before anyone warned the pilot.

Contaminated fuel is a big issue. It may not show up right away. You may have to work to get it out of your aircraft system, including just getting it to the low point in the tanks. Don't worry about moving water away from the low points. Worry about getting it to them in the first place. Entrained water may take a half-hour to settle out of the fuel; sumping right after you fuel may not accomplish anything. Let it settle, move or shake the airplane to get the fuel to the sump points, sump again. Sump as part of your post flight, too.

[IO540]

Simply towing the airplane or moving it a little way can help move water to the lowest point.

Why would the water not flow to the lowest point by itself?

[Mariner9]

Surface tension can lead to some water globules clinging to tank surfaces and not reaching the drains.

Not 5 minutes of draining worth though!

[IO540]

It would be easier to fit new o-rings on the filler caps!

[gasax]

I've had ice in both wings tanks. The aircraft was a Beeagle Terrier which has drains where you would expect - at the lowest point in the tank when parked.

Very noticeable as they was no flow when the drains were opened. Only other instance of 'finding water' was a C182 with bladder tanks - but they are notorious for ripples developing in the tank bottoms and stopping water reaching the drains.

[SNS3Guppy]

Not much point in having a drain point anywhere other than the lowest point in the tank.


You bet there is. Pilots are often surprised, (though they really shouldn't be) that water can collect at numerous other locations in the fuel cell(s) than the lowest point in the wing. Water is trapped behind baffles and tank support structure, in wrinkles in fuel cells, etc...and it can be a whole lot more than you think. Litres or gallons worth, in fact. Again, as stated before, this is the reason that more recent single Cessnas have multiple fuel drains under the wing. Even with a significant dihedral, you have no gaurantee of removing water and contaminants if you simply drain from the lowest point and call it good.

Another consideration is actually knowing where all the drain points are. A good example is the Cessna 206. Aside from wing drain points and the engine, the kidney sumps beneath the wing roots on each side have drain points...which are often missed by pilots who don't know to look there. These points have been found to contain significant water, and actually represent the lowest point in the wing fuel cell...even though they're not actually in the wing. Further, these represent the point from which fuel is drawn to the engine fuel filter and then the engine. You can start the engines on the existing fuel and suffer a failure shortly after takeoff if careful attention isn't paid here...especially for those who engage in the bad habit of switching tanks just before takeoff.

Why would the water not flow to the lowest point by itself?


Again, the interior structure of the tank may very well prevent water ending up at the drains where you might expect it. Water may have to be moved past barriers inside the tank to get to those drains. Often tanks may have internal ribs with lightening holes. These holes are generally not flush with the bottom of the tank, so water can accumulate on the uphill side of the baffle or rib, below the edge of the lightening hole...enough water to easily cause your engine to quit.

What's disturbing is that flight instructors these days don't seem to know this...and aren't passing it on.

I'll link you to a site below. The site (sumpthis.com) has some good pictures illustrating trapped or retained water. I've had some fairly strong disagreements with the person who started that site in the past, primarily over some insanely stupid actions on his part that he's elected to blame on the manufacturer. However there is still some good information if you're able to sift out his efforts to gather information for a law suit.

http://www.sumpthis.com

The message board has been taken down, apparently...I had some fairly scathing commentary there for a few years...but some information of use is still to be had.

Not 5 minutes of draining worth though!


Actually yes. I've seen many occasions in which an initial sampling showed nothing. Rocking the wings or moving the airplane and waiting produced water in subsequent samples...and the amount continued to increase. If you've just fueled, you may not be seeing the water for up to 30 minutes after the fueling is completed...and if you're flying a turbine aircraft it may be much longer (as turbine fuels suspend moisture much more readily than avgas).

[sooty615]

IO540

Basic physics can be used to work out the maximum possible amount of water that could collect in a fuel tank of a given volume. It is suprisingly small - a few cubic cm for most GA types.

I would be interested to learn the formula that one should use to make the calculation - nothing too complicated, just basic stuff please.

PS. IO-540 - great engine by the way :ok:

[magpienja]

I should know this but will ice float on top of avgas.

Nick.

[Mariner9]

I would be interested to learn the formula that one should use to make the calculation - nothing too complicated, just basic stuff please.
There is no requirement to measure water content in Avgas specs, so it is hardly ever done. (The presense or otherwise of water is determined only by the visual appearance of the fuel)

The amount of water that could be dissolved is dependant on many things including fuel components and temperature. I would say it would be safe to assume that the maximum amount of dissolved water in an Avgas would be ~200ppm.

Therefore, to obtain maximum dissolved water present in your fuel, multiply volume by 0.0002. (To simplify things, multiply fuel volume in litres by 0.2 or in US Galls by 0.8 to get maximum water volume in cc) However, this will not tell you the maximum possible water that could be present in your tank, water ingress could have arisen through external leaks or internal condensation of the air space above the fuel.

To answer Nick's question - frozen water has a density of ~0.92, Avgas has a density of ~0.75, therefore ice will not float!

[IO540]

I would be interested to learn the formula that one should use to make the calculation - nothing too complicated, just basic stuff please.

I don't have it but read the derivation in Usenet a few years ago. It appears simple enough: start with a worst case RH value (100%) and look up in some table the water mass per cubic metre at a plausible worst case ambient (say +35C; the higher this is the more water mass the air can hold) and work out the mass of water which would fit into your fuel tank's air volume.

It was just a few cubic cm for typical GA types.

It could in theory be worse but there are very few places on the earth where you will get high RH and high OAT at the same time. I suspect 100% RH and +35C would be extremely uncomfortable for humans too since sweating would cease to function as a means of body temperature control.

In Europe, 100% RH is rarely reached with an OAT above +20C, AFAIK.

[Lasiorhinus]

It could in theory be worse but there are very few places on the earth where you will get high RH and high OAT at the same time. I suspect 100% RH and +35C would be extremely uncomfortable for humans too since sweating would cease to function as a means of body temperature control.



Anywhere in the tropics spends most of the year at humidity close to 100, and high air temperatures. Yes, it is uncomfortable until you get used to it.
Sweating is still an effective means of temperature control, but only when there is some wind. Walk down Orchard Road in Singapore, and if theres no wind, you will melt. But even the slightest breeze and you start to feel human again.