AVIATION – JET FUEL
FUELSTAT®, The Aviation Fuel Test
With the FUELSTAT® aviation on site fuel test all you need is 10 minutes, a flat, clean surface, a pair of latex gloves & a 200 ml sample to discover which bugs are living in your fuel. The easy to interpret, pregnancy-style test gives a negligible, low or high reading which corresponds to the limits laid down in the IATA Guidance Material on Microbial Contamination in Aviation Fuel tanks. This clearly indicates the aircraft’s fuel system status, and what action to take, if any.
The Jet Fuel Fungus Problem
Microbes thrive wherever there is food and water. Aviation fuel systems are therefore ideal habitats for bacteria, yeasts and moulds. Bugs which grow unchecked can block fuel filters, cause gauging problems and are so corrosive, they can damage the aircraft tank structure.
Hormoconis resinae in Aviation Kerosene
Micro organisms can grow in certain fuels by using the alkanes in the fuel as a foodstuff. In some cases, they may be able to utilise some of the additives in the fuel. Mid to light distillate fuels are particularly susceptible to contamination by micro-organisms, although more recently there are increasing reports of gasoline being affected, particularly some of the more “environmentally friendly” products. The type of organisms and the damage inflicted depend upon on the fuel and the additives. All contamination is important when considering the quality of a fuel, particularly when monitoring stored products and reserves. A wide range of micro-organisms can be found in fuels in aircraft tanks and, if left unchecked, can cause damage to the tanks, the most serious organism is the filamentous fungus H. res.
Effects of Jet Fuel Contamination
H. res when compared to single cell yeasts and moulds produces far more biomass and is thus more likely to cause fuel blockage problems. If this happens to an aircraft engine during flight, or a marine diesel during operations in restricted waters or heavy seas, the impact can be catastrophic
H. res is by far the most common cause of microbial corrosion in aircraft tanks. Other organisms are more important in other circumstances, for example, in some ship fuels and in long-term storage. Other important corrosive organisms are the anaerobic bacteria, collectively known as Sulphate Reducing Bacteria (SRB) or, more accurately, Sulphide Generating Bacteria (SGB). These are not common in aircraft wing tanks because of the high level of aeration produced during flight and refuelling. Other filamentous fungi may be emerging as important, but these tend not to occur without H. res. being present and, in any case, are not currently very common.
Because of the way H. res. grows between fuel and water, it usually starts on small water droplets. It then covers the droplet, holding it in place, and continues its growth, actually generating more water under the mat due to its metabolism. In the process, it firmly attaches itself to the tank. Bacteria and yeasts require free water and are found, mainly, floating in the water phase. This means that they are less likely to adhere to surfaces and will, therefore, be significantly reduced at each water drain. H. res., once established, continues to multiply in situ. In aircraft, high levels of bacteria and yeasts tend to indicate that you have picked up poor quality fuel and, as such, are useful indicators. However, this does not necessarily mean that they are causing any problem in the tank, and they will probably be significantly reduced at the next drain. High levels of H. res., however, indicate that there is, potentially, a serious problem.
The Jet Fuel Fungus Solution There is no magic bullet to eliminate the problem. A multi-disciplinary approach to fuel hygiene is the key to avoiding the inconvenience and cost of a contaminated fuel tank. Good fuel hygiene entails implementing a risk assessed “rigid housekeeping regime”. The risk of contamination is increased in hot, humid conditions, especially where fuel comes from a source that has fewer quality control checks. Each airline should carry out its own risk assessment to establish an optimum regime. The selected regime should consist of regular water drain checks and at least an annual test of the fuel in every tank, followed by an appropriate fuel tank treatment, if required. Moderate levels of contamination require the use of an approved biocide. Heavy levels of contamination require the tank to emptied, cleaned and a biocide applied.