You Know Your Plane – Do You Know Your Fuel?

Know Your Fuel

Crowley delivers two grades of aviation fuel to its customers: AvGas 100LL and Jet A. Knowing what type of fuel an aircraft requires and what it looks like is priority one when it comes to ensuring safe operations. AvGas is dyed blue in color and Jet A is clear to straw-colored. It is important to verify what fuel is being delivered to your tank or aircraft with the delivery person and visually check the fuel before delivery or receipt is accepted.

Potential Contaminants Found in Aviation Fuel

Removing potential contaminants from your fuel tank is the most important aspect of ensuring clean and dry fuel for the aircraft. Visually inspecting your fuel tank or fuel source on a regular basis can prevent a major catastrophic event. The most common types of contamination seen to the naked eye are water, particulates or solids, surfactants, and microorganisms. 

Water is the most common contaminant in aviation fuel. It can be in the form of free water or entrained (suspended) water. Free water may be small water droplets in the fuel that settle on the bottom of a tank. Entrained or suspended water (mixed with fuel) may create a haze or appear cloudy, especially after being agitated from movement. The easiest way to remove water in fuel is to “sump” or purge the water from a low point drain on a bulk tank or the aircraft fuel tank daily. A Velcon Hydrokit can be used in the field to detect the amount of suspended water content in Jet A. This test uses a small glass jar and water-sensitive, powder-filled vial, similar to that used for a blood draw. Fill the vial with a clean fuel sample from a white bucket. Shake the vial for 15 seconds and wait 2 minutes, comparing the powder color to a paper chart. If the powder is darker than chart, it is a “fail.” Depending on the test utilized, it will indicate there is more than 15 or 30 parts per million (PPM) of water present. The allowable limit for suspended water in Jet A is 30 PPM into the wing of an aircraft.

Particulates or solids are anything that does not dissolve in fuel, such as rust, scale, sand, dirt, and metal. Fuel can collect solid contaminants at every stage of movement from the refinery to the aircraft. Particulates can pose problems once inside the aircraft leading to clogged filters, injectors, and wear and tear on the engine. Like water, the best prevention is to “sump” or purge particulates from the filter vessel while under pressure. Sump the storage tank or the aircraft fuel tank daily. 

Surfactants (or SURFace ACTive AgeNTS) are soaps or detergents that are common in the manufacturing of aviation fuels. When a refinery produces Jet A or AvGas, it processes the fuel through a clay treater to remove any surfactants prior to distribution. A surfactant will interrupt the surface tension of the fuel and prevent water from separating from the fuel during filtration. Surfactants may be introduced from contamination by fuel additives clinging to internal surfaces of tanks or pipelines. Soap and detergents will bind to filter elements and may render them ineffective. The only way to remove surfactants from fuel is to filter through clay filters, made with clay originating from Attapulgus, Georgia. 

Microorganisms are naturally occurring in fuel. When free water is present in the fuel, this creates a breeding ground for bugs. Bugs or microbes can multiply by the thousands very quickly, especially in a humid environment. Microbial growth may look like dark sludge in the bottom of your fuel tank, a very slimy brown substance that smells like rotten eggs. When microbes grow and multiply, they can cause corrosion inside tanks, clog filter elements, or even worse, cause damage to fuel systems in an aircraft. Again, the best way to prevent microbial growth is to sump or purge fuel tanks daily.

The last potential contamination can occur when fuels are co-mingled or mixed inadvertently. It is difficult to visually determine when aviation fuel has been contaminated. Testing the American Petroleum Institute (API) gravity, or specific gravity of the fuel, is the only way to ensure fuel is on specification in the field. This is easily done with a white bucket, a sample of fuel and a thermal hydrometer. You can also ask your fuel provider to review the Bill of Lading or Certificate of Analysis (COA). The COA of aviation fuel is the “birth certificate of the fuel.” A total of 20 ASTM tests are performed on Jet A and 16 on AvGas to certify the fuel is within required ASTM standards before the fuel can be released by the refinery for distribution. The tolerance allowed for aviation fuel is 1 degree +/- of API from the original COA. The delivery driver will have this paperwork and is required to test prior to making a delivery. 

Jet A typically ranges between 39—51 degrees of API, and AvGas ranges between 59—71. However, anomalies can occur, such as last summer when Alaska experienced a hotter than usual ambient air temperature and a load of AvGas delivered in May from California was testing between 71—73 degrees of API.

Testing for Contamination in the Field

Crowley utilizes several types of testing to ensure fuel is on specification prior to delivery in the field. 

A white bucket test is used to visually inspect for water, particulates (solids) and microbial debris. This test is conducted using a clean, white, porcelain-lined bucket equipped with a static bonding cable. A sample is taken from the low point drain of the tank and the fuel sample is evaluated for water, particulates, microbial contamination, or any other condition indicating product contamination. Depending on the results, additional tests may need to be run. The sample is rated for visual appearance to describe possible contaminants and moisture content. If the fuel does not pass the inspection during the testing process, another sump is taken. If after five sumps, the sample does not pass, then no fuel is delivered.

Want a simple trick to know if you have clean fuel? Take a sample of your fuel in a clean, white bucket and drop a penny in the bottom. You should be able to clearly view the defining marks on the head or tails of the coin.

A clear and bright test is conducted using a clear Mason jar. Once a white bucket test is completed, take a clean Mason jar and dip it into the white bucket. Hold the jar and swirl the fuel inside until it creates a vortex. The vortex should appear clear and bright. If contaminants are present, they will haze the fuel (such as water), appear shiny (metals) or bubble (surfactants) on the surface. Once the sample settles, blow on the surface of the fuel. If the bubbles dissipate quickly, then you have a clear and bright sample or fuel free of these types of contaminants.  

“API Gravity” or “specific gravity” is a measurement of fuel density. A significant change in fuel density is a sign there may have been cross-contamination by another product. This test is done by correcting the observed API to 60 degrees F and comparing it to the API on the Bill of Lading or the Certificate of Analysis to check for a variance. The allowed tolerance of aviation fuel is 1 degree +/- of API when delivered into wing. 

Another test utilized to determine if fuel is on specification is to conduct a “flash” of the fuel. However, this test must be performed in a controlled laboratory environment with calibrated equipment. “Flash Point” is the lowest temperature at which a liquid gives off enough vapor that it will ignite under specific test conditions. This test is used to determine at what temperature range aviation fuel will flash and verify the actual flash point of the fuel is within specification tolerances. Jet A has a minimum flash point of 100˚ F and AvGas is minus 45 degrees F.

What Should You Do Once You’ve Received Fuel?

Maintenance of your fuel system is equally important once you’ve taken receipt of or accepted the fuel into your tank. Crowley calls this the point of custody transfer and control of the fuel, which occurs when fuel is transferred from Crowley’s delivery truck into your tank or aircraft. It is key to continue monitoring your fuel system to ensure you maintain the fuel quality. Inspections should be made daily, weekly, monthly, quarterly and/or annually depending on the product stored and how it is utilized. The closer you monitor the fuel system, the less issues can arise. If you are sumping your fuel tank daily, then you have less risk of water accumulating in the filter element.  

Also, look for anomalies in the fuel system. Is the fuel sample a different color than the day before? What has occurred since you last took a sample? Did you take delivery of fuel? Did someone forget to close the gauging hatch on the tank? Has condensation built up inside a tank due to severe temperature swings from cold to warm, or vice versa? The key is knowing what to look for and monitoring your fuel source frequently. For more information, resources can be found at www.airlines.org or www.astm.org.

When in Doubt, Consult Your Crowley Fuels Experts

“Having an acute knowledge of aviation fuel quality and a willingness to share it freely and often with aviators is what sets Crowley apart from the competition,” Croffut says. 

“With customers across every region of the state, I travel frequently to our fuel terminals where we dispense aviation fuels,” says Craig. “I see lots of aviation fuel tanks and field questions on a regular basis regarding fuel quality control. We feel the need and responsibility to educate our customers on how to care for the aviation fuels we deliver. Our commitment doesn’t end at the hose connection. Our employees, customers, and families fly on the aircraft we provide fuel for, so it’s important to help keep everyone safe.” 

Crowley frequently invites its customers to attend aviation fuel quality control handling classes. As one customer said after attending class, “Fuel is the lifeblood of our industry. We can’t go anywhere without clean and dry fuel.” Organizations interested in having employees attend an upcoming class are encouraged to contact their Crowley Fuels salesperson or Sara Craig, Crowley Fuels quality control manager, at 907-777-5409.

“We understand how integral the aviation industry is in Alaska for businesses and residents,” says Rick Meidel, Crowley Fuels Alaska vice president. “We make safety and dependability a central part of how we operate every day, and that translates into a strong relationship with our customers.”