Sloshed Tanks, Big Problems

Sloshing‘ is a process where a fuel tank sealant is put into a metal fuel tank, and the tank is rocked back and forth, to evenly distribute the sealant … it has nothing to do with beer. If you are an airplane mechanic, you probably well know what a ‘sloshed tank‘ is. When done properly, the sealant fills any gaps in the seams of the fuel tank, and is then allowed to dry. This in turn allows the tank to be used and not leak fuel, which is always a good thing.

SOMETIMES THE SLOSH MATERIAL DOESN’T STAY ATTACHED. Such was the case with the owner of a Cessna 140 at our airport. The other day, he dutifully filled his fuel tanks to the top, and sumped them to remove any water or debris. What he saw in his fuel sample was the first symptom — a small quantity of material that looked like ‘bees wings,‘ or the tiny pink-red flakes from harvested corn. Since our airport is near a cornfield, he may have somehow reasoned farm-related contamination.

After sumping the tank until the material no longer appeared, our pilot started up his engine and taxied out to the active runway for departure. His engine runup went well, and as he took the runway and advanced the throttle, the plane accelerated normally and picked up speed as he expected it to. He lifted off at the normal speed, and began his climb to pattern altitude.

AS HE REACHED PATTERN ALTITUDE, THE ENGINE STARTED TO SPUTTER AND SHAKE. The pilot quickly checked his carb heat, which was off. Carb heat went to full, but did not improve the situation. He ran through his emergency checklist, and confirmed he was full of fuel as he turned back towards the airport. Our pilot rightly declared an emergency to clear the pattern, and set up to make an immediate landing.

Wrangling with the 140 at low power, our pilot did manage to make his way down and land the plane. Once on the ground and at the FBO, the engine fuel strainer was inspected and revealed that it was loaded with these tiny flakes of material. A closer inspection revealed a substance that looked like onion cloth — very thin slices of a nearly translucent material.

THE FBO’s MECHANIC WAS OLD AND WELL VERSED, and quickly identified the source of the material as the fuel tank. A quick look through the filler with an inspection mirror and a light showed that the sealant was flaking off the inside of the tank, and was suspended in the fuel inside of the tank!

BOY, DID OUR PILOT GET LUCKY. He made one mistake in judgment, which got him a whole lot of emergency procedure experience in one shot. When he saw the material in his fuel tester, he incorrectly assumed it was from the corn. Problem: Our brains always seek a solution; often in the absence of a good one we’ll settle for one that best suits our desires. In this case, it wasn’t anywhere near harvest time … not that harvest time would make it much easier for corn residue to get into the fuel in the first place. No source of materials means that the stuff he found could not be from the harvest — ergo, he did not find the problem.

HE DID SUMP THE TANK RIGHT. After he found signs of contamination, he sumped the tank until all traces disappeared. While the material was found in suspension in the fuel tank, it is likely that it was flaking off. The plane’s motion as it taxied likely disturbed the flakes, and ultimately they got into the strainer where he found them. Over time, running the plane and going for a ride disturbs the flakes even more, causing them to break off en mass, and ultimately resulting in a loss of engine power as the strainer became clogged with debris.

WERE YOUR TANKS SLOSHED? Do you have a ‘ticking slosh bomb‘ waiting to go off the next time you throttle up and climb into the sky? The only way you will know is to ask your mechanic and review your log books. Your mechanic knows what a sloshed tank looks like, and once identified, he can inspect the tank for coating breakdown. The coating is so thin that the untrained eye might miss it — you can look, but if you don’t see a coating that doesn’t mean it’s not there. Ask your mechanic to check for one as well.

DON’T PRECONDITION YOUR MECHANIC BY TELLING HIM WHAT YOU DIDN’T SEE. Let the mechanic look and determine for him or herself what the condition of the tank is. If you ask them to look, but tell them that you already did and did not see anything, it may subconsciously influence the mechanic who may then take a more cursory glance. This exposes you to more risk if they don’t find the problem.

BOTTOM LINE: If anything turns up in your fuel, you need to identify the source. Fuel contamination is nothing to trifle with, and to be blunt, the only thing you should see in your fuel sump checker is FUEL — PERIOD. By maintaining zero-tolerance to any foreign materials in your fuel, and having your sloshed fuel tanks inspected, you will be better protected against the slings and arrows that inconsistent fuel quality or bad fuel tank linings can occasionally throw at you.