Fuel contamination question...

[wrxpilot]

Hey guys,

I've got a quick question for you... It's been the standard practice for a long time to dump fuel samples on the ground when sumping the tanks. But in FL we have an environmental law against this. So most people sump the tanks, check the sample for contamination, and dump it back into the tank. Maybe I'm just too anal, but I really don't like doing this. Even if I have access to one of those fuel testers w/ a screen in it, I'll dump the fuel sample on the ground.

My feeling is that any small contamination (dirt, rust, etc.) that might possibly be introduced into the fuel tank would of course be captured by the fuel filter, but this may hasten the filter getting clogged. Smaller stuff may get by and build up in the carb jets or fuel injectors. Am I worrying about this too much? Just wondering what your guys feelings are on this. Thanks!

 

[jknight8907]

If the sample is clean and the tester is clean, it should be fine to dump it back in. If you're really worried get one of those GATTS jars that has a filter which catches everything including water.

 

[Gatorman]

The primary purpose for taking fuel samples is not for removing debris, you are correct that that is the job of the filter. The purpose is to remove any water that collects in the fuel cells.

I have told by an airport official that small amounts of fuel can be poured out on the ramp and swept out to evaporate on the concrete by the sun.

Also, since I am now at a different field, we collect the samples in 55 gallon drums for pick up by a local farmer who uses it in his tractor and as a weed killer...go figure?!?

 

[jknight8907]

He uses Jet A or 100LL?

If 100LL, daaaaaaaaaaaaaaaaaaang! Some tractor...

 

[avbug]

I believe he's talking about jet. It's nearly the same as #2 diesel, and burns great in any tractor. We've burned #2 diesel in ag airplanes for eons, too.

Neither Jet nor Avgas is used as a herbicide, but is used as a carrier, and has been for many years. Jet or diesel, that is. Back when it was a whole lot less expensive. It's put out typically with certain herbicides such as 2,4-D to improve dispersion and adhesion on broadleaf plants and to control drift and vaporization. This isn't common use in aircraft aerial application any more, but it used to be.

As far as fuel sampling, when I was just out of high school, my first ag employer used to have us start the day at the first fueling by running the first fuel out of the hose onto the ground, a gallon or so. It was used to clear the line and ensure that no contaminates were found; we could sample that gallon, if we liked.

He used to say it was the cheapest fuel he bought. The idea of catching it and putting it back was unheard of.

Most turbine operators discourage pilots from sampling fuel, anyway. It's relegated to more of a maintenance function as part of the daily inspection.

 

[hawg2hawk]

Most turbine operators discourage pilots from sampling fuel, anyway.

I've noticed that too, but never thought to ask why. The only jet fuel I've ever sampled was from UH-1's at Fort Rucker.
Do you know why?
Not that I'm complaining.

 

[avbug]

Several reasons. Water doesn't settle out in jet fuel like it does in avgas, it tends to stay in suspension or entrained. Sampling doesn't always do much good. Sampling can cause a petcock or drain to continue weaping or leaking, which can cause a lot of problems and loss of revenue, as well as make the aircraft look bad. Sampling may not find anything, even though moisture is suspended in the fuel, and unlike sampling fuel on a Cessna 182, downing the aircraft long enough to address the problem when the petcock sticks may mean thousands of dollars of revenue lost, instead of tens of dollars.

Much like the dog in the cockpit theory, management generally understands that pilots are idiots (something most mechanics know all too well)...eliminating one more way for a pilot to break an airplane makes sense.

Turbine aircraft fly higher, into colder places. Especially on a turn around, fuel seals on drains can stick or take a set and not reseat, and will continue leaking, whereas most aircraft burning avgas don't experience this problem much, if at all.

Jet fuel is more slippery than avgas, and tends to keep seeping or leaking past drains once opened. The general consensus is to leave them alone if they're not broken. I dont know if I'd entirely agree, but it's also true that sampling the fuel won't necessarily tell you if you have contamination...it's often suspended due to higher viscosity. Opening the fuel drain doesn't necessarily help, except with heavy, solid accumulations of contamination.

Unlike a piston engine, running small amounts of contamiantion through the turbine engine, where fuel flows are higher, the contamination can be more easily tolerated, and it's not nearly such a big deal. A much bigger concern is the risk of fuel flow stoppage or restriction due to freezing on fuel filters, and it's for this reason that fuel additives such as Prist are utilized in day to day operations.