How can I ensure an FBO’s fuel is not contaminated?

I recently received an email from a pilot who was wondering how he could ensure that the 100LL he was getting at airports during a cross-country flight was on spec and not contaminated.

A good question, but one that does not have a good, clear answer.

The main cause of off spec 100LL is water and associated contaminates in the fuel.

Water can come from condensate, leaking storage tank roofs, or a number of other sources. The bottom line is that water is going to be in the system.

There are several ways that the water is handled so that it does not cause major problems.

The first is called floating suction and is on all FBO and 100LL distribution tanks.

Since water is heavier than fuel, it will settle to the bottom and clean fuel can be pulled off the top surface.

But the floats can leak over time and just sit on the bottom. When fuel is pulled out of the tank it pulls off the bottom and will pull in any water and contaminates that are at the bottom of the tank.

For this system to work well, the tank bottoms need to be drained periodically. The float on the suction line needs to be checked to ensure that it is still floating.

And the tank needs to be shut down after any fuel deliveries to allow for contaminates to settle out before anyone starts to pump fuel out of the tank.

A side note: If you drive your car into a mogas service station, and there is a tank truck unloading there, drive on to another station or wait several hours until that tank settles out.

A second method for removing water and other contaminates is with a filter separator vessel.

These units have a coalescing element that causes water mist type particles to coalesce into larger droplets. A second element in the vessel filters out these droplets and they fall to the bottom of the tank where they can be drained off. The separator elements are usually a fine Teflon coated screen.

The third method that is used in some places is filter elements that have special water-absorbing paper in addition to the filter medium to ensure against any water getting into your aircraft.

The fuel systems at most FBOs contain at least the first two methods. The question is whether or not their personnel check and maintain their system.

They need to periodically check the float and drain off the water and contaminates from the water draw built into their tanks.

Occasionally tanks will settle in the ground so that the water draw is no longer the lowest point in the tank. This will result in some water and contaminates remaining at the bottom of the tank, making the settling time that much more important.

The filter separators also need some care and maintenance. The separator screens need to be tested periodically and handled properly because a fingerprint can negate the element’s performance and allow water to pass through.

Also, coalescing elements need to be checked and replaced periodically.

In addition, performance data, like pressure drops across the filter elements, must be recorded daily to monitor the operation of the system.

Another concern is if you are using mogas. A few years ago, a fuel dealer delivered ethanol-free regular gasoline to my farm. What we found out later was that he had delivered regular gas with ethanol on his previous delivery, so the hose reel was full of ethanol-containing fuel, which went into my tank and shut down most of my equipment.

The bottom line is none of these systems can be checked by the pilots. Pilots can check equipment like fire extinguishers and ground cables, as well as check on the Internet for any negative reports — but most internet comments are about the bathrooms and coffee machines.

Now as far as what a pilot can do, be patient when refueling. I know most of you are in a hurry and want to get to your destination on time.

But I recommend that you let your plane sit for maybe a half hour or so after fueling before you do your fuel sump checks. That way, if you did get some moisture or contaminates, you would have a better chance of spotting it.