N527TS Fuel Contamination

[iaw4]

 

I just read the report on N527TS

http://www.kathrynsreport.com/2016/07/flight-design-ctls-accident-occurred.html

It seems that the fuel had too much water in it.  what kind of fuel or neglect would cause this sort of problem?

[Mike Koerner]

ia,

I know nothing about the aircraft or the pilot in the report you linked. I'm not even sure the report indicates water in the fuel. Corrosion on the carburator slide could be from water condensing out of the air as the plane sits on the ground. I'll respond to your question on water in the fuel anyway:

The report indicates the aircraft was using aviation fuel. Water separates out of aviation fuel like 100LL. It's heavier so it will drop to the bottom of the wing tanks and then out the wing drains to the gascolator. The gascolator is designed to separate and collect the water. It has a drain on the bottom to allow you to periodically remove any water that it accumulates. If you are using aviation fuel, before each flight you should check for water in the gascolator by draining a bit into a glass. Again, it separates from the fuel so it will readily show up in the bottom of the glass. If you’re not sure what it looks like, just add a little water to the fuel the first time so you get the picture. If there is water present, drain some more fuel out until the fuel runs clean.

Cessnas have drains under each wing to check for water. We don't and we have less dihedral. So, it might be a good idea to walk out to a wing tip and rock the plane back and forth a few times to encourage the water to flow down into the gascolator. That said, the fuel lines are so small I'm not sure how effective this will be.

Water may already be in the fuel you use to fill the plane. This is seldom a problem but something to consider at little airports where the fuel may sit around a while. More commonly, the water comes into your tanks separately. Maybe you leave the plane outside and one of the fuel cap seals is leaking allowing rain water to get in. Most commonly, moisture gets in the tanks through the vents as the tanks "breathe". Fuel contracts as it cools, such as during the night. As a result, air is sucked into the tanks to maintain the ambient pressure. Some of the water vapor in the air may condense inside the tanks. The next day the fuel warms up and some air is expelled but the liquid water has already fallen to the bottom of the tank.

Interestingly, water ingestion will be greatly increased if the plane is left setting outside, uncovered on a clear, still night. This is because the aircraft radiates heat to deep space. It gets colder than it would in a hangar. In fact, the surface gets colder than the ambient air temperature which enhances both the air ingestion and water condensation in the tanks.

Common guidance is to keep your tanks topped off to reduce water ingestion. I'm skeptical of the effectiveness of this. More fuel means more thermal contraction and thus more air and water vapor entering the tanks. The only advantage would be that the larger heat capacity of the full fuel tanks reduces the temperature swing.

Finally, planes in humid or coastal areas (like Wisconsin, or the LA basin) are much more susceptible than aircraft in dryer climates (like desert areas, or even Van Nuys).

Aircraft using unleaded fuels blended with alcohol (most autofuel in the US) are much less susceptible. This is because the water dissolves in the alcohol, which is dissolved in the fuel. The water doesn't separate and causes no problem to engine operation. There is a limit to how much water can dissolve in the alcohol but it doesn't seem likely that we will reach that limit (unless the fuel caps are left off in the rain). I use autofuel almost exclusively and have never seen water in my fuel. In fact, I seldom bother to check for it.

Has anyone reached the water saturation level with autofuel?

Mike Koerner

[Ed Cesnalis]

4 hours ago, Mike Koerner said:

Has anyone reached the water saturation level with autofuel?

No, not in 12 years with my CT and or 2 years with prior Rotax powered plane.  Then again I fly out of Mammoth where moisture is not permitted.

[Roger Lee]

I overhaul carbs and yes I have seen corrosion in bowls, but usually very minor because most keep their planes in hangars. I had one of the worst ever from Florida that had been left outside. When I took the bowl off it was about 1/8" thick with white corrosion over the entire bowl surface. I tried to clean the bowls, but the water corrosion had eaten down into the bowl surface and pitted it beyond belief. Those bowls had to be replaced at about $100 a piece

It is not unusually to see a tiny spec on the bottom of the bowl where a drop or so of water has been.

It is easier to see water separating out of 100LL and of course you find it at the low point drain. Finding with saturation and separation in an ethanol fuel is possible, but I have never seen or even heard of that because it would take one hec of a lot of water poured into the fuel tank and I don't think most pilots are that stupid. If you ever saw water in an ethanol fuel then the fuel must be completely drained because that does mean it is fully saturated.

[iaw4]

 

thank you.  this is yet another good reason (not lead related) why autofuel is the better choice for rotax engines.  I only wish some local airports around here carried it.

 

 

[Warmi]

Well, I presume non-ethanol mogas and UL94 suffers from the same problem like 100Ll right ?

[Roger Lee]

Any fuel that has no ethanol will separate from the water. Ethanol will absorb a % water per volume of ethanol. This can at times be helpful, but no matter what fuel you use getting too much water in the system from contaminated fuel or leaving it in the rain can cause issues. If you are aware of those issues they can be avoid or at the very least mitigated if they occur. 

[Tom Baker]

A few years ago I removed the bowls from a CT that was using Avgas during troubleshooting. I sat the bowls on a table in the hangar for a little bit. It was very hot and humid 100° plus with 90%+ humidity. The cooling effect from the evaporation of the fuel was enough to condense the moisture from the air causing water droplets to form in the bowl.