When you pull up to the gas pump in your car, you probably don’t think much about what is in your fuel. Perhaps you try to find a certain brand based on the fuel card in your pocket, but usually price is the primary factor. What about when you’re fueling your aircraft? Most corporate aircraft pilots and operators are aware of the fuel system icing inhibitors (FSII) and biocides available as additives for jet-A and jet-A1. But what do these additives actually do, and how often should an owner/operator ensure these additives are introduced into the fuel loaded aboard?
Out of the nearly one dozen additives available for aviation fuels, including corrosion inhibitors, static dissipators and anti-oxidants, corporate pilots flying jet aircraft really have to concern themselves with only two additives: FSII and biocide.
All jet-A must meet the specifications set out in ASTM standard D1655-01, that dictates which particular compounds make up aviation turbine fuels. A similar standard, D4171, states the specification for an approved FSII additive, a compound called diethylene glycol monomethyl ether (DiEGME or DEGMME), which must be set in concentration of 1,000 to 1,500 parts per million (ppm) in jet-A.
As most corporate pilots are aware, jet fuel inevitably contains some water molecules that may have been introduced into the system from the refining process, contaminated fuel storage tanks and simple condensation in a partially empty fuel tank. As jet fuel cools at altitude, its capacity for containing water decreases, allowing the water molecules to collect and form larger droplets that can easily freeze in subzero temperatures. These small ice crystals can produce a host of in-flight problems as they plug fuel filters, clog fuel lines and block nozzles.
Most current production jets contain fuel heaters that warm the fuel shortly before it reaches the injector to thaw any ice crystals that may have formed. However, for those corporate aircraft that do not have fuel heaters installed, using an FSII allows the DiEGME compound to seek out and attach itself to any water molecules that may be present in the aircraft fuel system. This DiEGME surrounds each water molecule and reduces its freezing point to approximately -48 deg C, preventing the droplet from freezing in the tanks on the ground in extremely cold climates or at altitude.
“Using FSII is not solely a cold-country or cold-climate issue, since the subzero temperatures at altitude can cause any water in the fuel to freeze,” said Phil Botana, president of Portland, Ore.-based Flightcraft. “FSII is generally available at every FBO in some form since small Learjets and early Citations don’t have fuel heaters and are required by the manufacturer to have FSII added at every fueling to fly at certain altitudes.” The difference in freezing point with FSII added may, for example, allow a Learjet to fly at FL 420 instead of at FL 320, depending on the temperature.
But even if an aircraft has a fuel heater installed, its pilots should not systematically ignore using an FSII, such as Prist Aerospace’s Prist or Hammonds’ Fizzy, particularly if the aircraft will be sitting outside for an extended period of time in cold weather conditions.
“From a pilot’s perspective, I don’t see how it could hurt to use FSII when it is offered,” said Phil Fountain, a contract corporate pilot who flies a GII. “Even though the GII has a fuel heater, I wouldn’t hesitate to take it [FSII], especially if it’s only a penny or two a gallon more, and especially if there is any concern about contaminated fuel. Using Prist provides another level of safety.”
One reason to use FSII even if the aircraft is equipped with a fuel heater is that FSII does have some antimicrobial properties, even though EPA requirements currently preclude FSII manufacturers from making official biocide claims.
Killing the Bugs
Like water, microorganisms can find their way into jet fuel and create hazardous conditions. Various water-borne and airborne bacteria and fungi (otherwise known as yeasts and molds) can be introduced into the jet fuel and rapidly multiply to form scum that can wreak havoc on an aircraft’s fuel system.
“Microbial growths can live in the water particles suspended in jet fuel, and feed off the minerals and hydrocarbons in the fuel itself,” said Walter Chartrand, technical and operations training manager for Air BP. “Some microorganisms can double their mass in 20 minutes, creating a slimy substance in the fuel/water interface that can plug filters…Other organisms produce sulfuric waste, which combines with any water present to produce the sulfuric acid that leads to wing-tank corrosion.”
To combat microbial growths, many operators use a biocide such as Hammonds’ Biobor JF or Fuelcare’s Kathon as part of a semi-annual maintenance procedure. These biocides kill the microorganisms present in jet fuel, preventing additional growth, but they do not remove the actual “bodies” of the dead organisms that may be left behind if the system is badly contaminated. Serious contamination requires complete draining of the fuel system and thoroughly removing the scum by hand, using a high concentration of biocide.
“Good housekeeping is important in treating slime problems, but it is not a cure,” quips the Hammonds Web site (www.hammondscos.com), which says that Biobor JF should be used at a level of “270 ppm in fuel to effect sterilization, and subsequently at 135 ppm to maintain fungus-free fuel.” This suggests that jet operators who are using a biocide additive semi-annually during maintenance procedures might want to think about adding biocides to their jet fuel more frequently.
In fact, combating microorganisms might be a more important reason to use FSII than inhibiting icing, especially in aircraft that contain fuel heaters. It is widely known in the fuel industry that the FSII itself is a biostat, meaning that although it does not kill microorganisms, it will retard their growth. Research indicates that aircraft operators who consistently use an FSII additive reap benefits beyond ice prevention.
“Before 1994, Prist additive was made to MIL-I-27686(E), which specified ethylene glycol monomethyl ether (EGMME),” states the Prist Web Site (www.csdinc.org/prist/faq2.html). “We paid to have this product certified as a pesticide with the EPA, [which] allowed us to advertise the ability of Prist additive to retard growth of microbes in aviation fuels…With all of the new EPA requirements, it became economically prohibitive to certify the new DEGMME-based additive as a pesticide.”
Pre-blended or Injected?
One company, however, is in the midst of this testing and is working with the EPA to establish anti-microbial claims. Although the testing is not complete and claims cannot be made yet, ConocoPhillips, the only petroleum company in the U.S. currently offering pre-blended FSII with its Philjet A fuel, has seen enough benefits for customers who consistently use the pre-blended fuel to engage in the testing required to seek approval for the official biostat claims.
“Our FBOs have seen significant cost savings in maintaining cleaner fuel farms and fuel trucks from the consistent use of our pre-blended product,” said a representative for ConocoPhillips. “We estimate that an aircraft fleet owner using our product consistently can see annual savings of $30- to $40,000 per year in maintenance costs.”
ConocoPhillips pre-blends an FSII additive into Philjet A at the terminal, bypassing the need for the additive to be injected into the fuel later. Pricing for the Philjet A fuel then includes the FSII additive, whereas with other brands of jet-A fuel the additive usually costs two to four cents extra per gallon.
“If I have a choice, I’ll usually go with the pre-mixed Phillips 66 fuel versus another brand that does not have [FSII] pre-mixed,” said Doug Lea, a contract pilot who flies several types of corporate jet. “There’s usually a cost advantage to the pre-mixed fuel. Of course, many times the boss wants to go to a particular FBO for reasons other than the fuel, but we usually do talk about where we’re going to buy fuel.”
According to Carl Hammonds, president of The Hammonds Companies, which produces both Fizzy and Biobor JF and manufactures various additive injector systems, there can be problems inherent in pre-mixed fuel.
“The very property of FSII that is designed to have an affinity for water molecules makes FSII also fall out of fuel very quickly,” said Hammonds. “I’ve taken a beaker of jet-A, added a colored FSII to it, and within 30 seconds the FSII is down at the bottom of the beaker. In pre-mixed fuel, the FSII will fall out of the fuel due to either gravity or attraction to water, which is heavier than fuel and tends to sit at the bottom of the vessel as well.”
Hammonds noted that fuel pre-blended at the terminal could be handled as many as five times between the terminal and the skin of the aircraft, with a little more additive falling out or being filtered out at each handling. “The farther upstream in the fueling process you insert the additive, the more potential you have for a reduction in the final additive quantity by the time you get to the aircraft.”
Hammonds’ answer is to inject the additive into the fuel mixture as it is being added to the aircraft to ensure a consistent blend at the 1,000 to 1,500 ppm ASTM standard concentration. His company’s new Smart600 injector includes a computer display that gives a continuous readout of the additive-to-fuel ppm ratio. “If the injector system falls outside the high and low limits set, it not only shows the operator that it has fallen out of ASTM spec, but it also shuts the fuel off so there is no possibility of straying outside the spec,” Hammonds said.
He noted that once the FSII-laced fuel is added to the aircraft, the movement of the fuel through the aircraft system generally stirs the mixture enough to prevent the FSII from falling out, assuming the aircraft is not going to sit on the ground for an extended period of time.
Hammonds did acknowledge that if the fuel is pre-mixed at the upper end of the ASTM limit (1,500 ppm for FSII) at the terminal, then the fuel would likely still have an adequate amount of additive (1,000 ppm) by the time it reaches the aircraft.
Keeping the additive concentration within tolerance is a challenge that ChevronTexaco is looking at overcoming as it may soon be giving ConocoPhillips competition in the pre-blended arena. According to Tracy Boval, manager of product quality for ChevronTexaco’s Global Aviation division, the company is currently looking at the operational procedures needed to introduce pre-mixed FSII in its jet-A fuel.
“There is a lot involved in making sure that FBO personnel have the training and competency needed to test the fuel and ensure it continuously meets standards,” said Boval. “We will be imposing more stringent minimum and maximum standards to ensure the fuel is within tolerance.”
The Future of Additives
Although performance-enhancing additives are not currently allowed in jet-A, several companies offer or are testing additives in jet-A1 for overseas use. Shell Aviation currently offers the Shell AeroJet brand of jet-A1, which contains FSII, biocide and anti-static additives. And the company is working with KLM Royal Dutch Airlines and BetzDearborn on a performance additive that is designed to “keep fuel and injector systems clean, reduce exhaust emissions, improve fuel efficiency and lower maintenance costs.”
According to John Ambrust, publisher of World Jet Fuel Report, additives to cut down on carbon and sulfur emissions will soon be on the EPA’s radar screen as the U.S. agency monitors European efforts to reduce contrails. “CO2 emissions have a tendency to make the sky milky due to contrails and vapor trails,” said Ambrust. “By 2 p.m. the sky over Brussels is so milky that the sunlight is literally blocked out. As carbon taxes in Europe raise the price of jet fuel, it is quite likely additives that reduce the sulfur and carbon content, similar to those available for automobile gasoline, will become essential both in Europe and, later, in the U.S.”