South Africa has recently experienced a spate of incidents due to contaminated fuel, high compression engines are being affected in growing numbers. The problem has reached such a level that the SACAA have issued a warning and asked pilots to please supply samples of fuel that they deem to be suspect.
It is of critical importance that the fuel taken onboard at uplift is not contaminated in any way since the effects of any such contamination are likely to affect all engines and this may not be evident until after an aircraft has become airborne.
In common with one other subject also critical to aircraft operational safety, aircraft ground de/anti icing, the quality of fuel ‘into-plane’ has been omitted from the ICAO system of safety oversight and there are no corresponding SARPs. Some National Regulators have in recent times reacted to this situation by re-iterating the ultimate responsibility of aircraft operators to ensure that they adequately address fuel contamination risk with adequate “Policies, Standards and Procedures” (PSPs) without continuing very far into the presentation of guidance or the specification of requirements. Fortunately, the subject of fuel quality and the prevention of contamination has been the subject of very comprehensive attention from both the supplier and consumer parts of the industry and this activity and the purposes it serves have now been summarised in the first ICAO Document dedicated to fuel quality, "Doc 9977 Manual on Civil Aviation Jet Fuel Supply" (2012).
Once refined to specification and delivered as such to an on-airport storage facility, aviation fuel is drained on a daily basis to remove any water which may have resulted from condensation so as to minimise the chances of microbial proliferation. Before being taken from bulk storage and uplifted by an aircraft, fuel is then filtered as least twice to ensure that it is free from particulate matter which could affect aircraft fuel systems and to ensure that any remaining traces of free water are removed.
Large airports, where multiple fuel suppliers are likely be present, have since the 1970s seen the sharing by fuel supply companies of storage tanks and, where installed, hydrant systems. This trend was the direct trigger for the main oil companies to form the “Joint Inspection Group” (JIG) to develop a single set of standards to govern the operation of such shared facilities and ensure that they supported the maintenance of fuel quality. The JIG is a not-for-profit company with over 60 members which defines aviation fuel Standards and operates a quality assurance inspection process which validates their application. JIG 1 covers operating standards for into-plane fuelling services and JIG 2 covers operating standards for airport depots. Both are endorsed by IATA which, along with many new entrants to the aviation fuel supply business who are not also major oil refiners (who are the core JIG membership) is an Associate Member of the Group. Associate Members now form the majority of the JIG membership. Standards JIG 1 and JIG 2 have been complimented by JIG 3 which covers operating standards prior to airport delivery and an additional Standard, JIG 4, which covers operating standards at smaller airports, has recently been issued.
In 2011, JIG Standards were being directly applied to shared facilities at about 180 of the world’s major airports as well as at many smaller airports where Member Companies are the sole suppliers or where the Standards are used as a reference. The result is that an estimated 2500 airports and approximately 40% of the world aviation fuel supply is covered by JIG Standards. The JIG has noted that their standards have effectively become the de facto global standard for aviation fuel quality control.
In recent years, the Energy Institute (EI) has become more involved in aviation fuel standards and in a new joint initiative which now effectively enhances and replaces JIG 3, the EI and the JIG have developed and issued (November 2013) a new EI/JIG Standard 1530 on “Quality Assurance requirements for the manufacture, storage and distribution of aviation fuels to airports”. This comprehensively addresses all aspects of fuel quality upstream of airports and includes both mandatory requirements and best practice guidance. Whilst this new Standard has been prepared in the context of the European legislative and regulatory framework, it is noted that its provisions “can be similarly applied in other countries providing national and local statutory requirements are complied with”. It is broadly compatible with equivalent Standards published by the American Petroleum Institute (API).
The most common contaminants are particulates, water, other petroleum products or their residues and microbial growth:
Particulates - despite the increasing use of protective coatings on the interior surfaces of fuel tanks and pipes predominantly made of steel or its alloys, the main source of particulate contamination is rust and scale. The presence of even small quantities of water ensures that almost any distribution process will be the source of some rust contamination. Other sources of particulates include airborne solids that enter through tank vents or slip past the seals of floating roof tanks (dust and pollen), solids entering through from damaged hoses and filters (especially rubber particles and fibres) and solids from microbial infestation (cellular debris and
Water - the accumulation of water is almost inevitable in stored aviation fuels even if it has a low water content at airport delivery because of a number of opportunities for moisture to be taken up. These include free water in low spots in a pipeline, rain water leaking past the seals in floating-roof tanks and moist outside air entering the vents of fixed roof storage tanks. Air flowing in and out of a fixed-roof tank as fuel is added or removed may also change the moisture content of air in contact with fuel. The temperature of the fuel itself may change in association with the diurnal variation in outside air temperature or for other reasons so that the chances of water condensing out (or not being absorbed) are altered. Also, if fuel from underground tanks or pipelines is cooled during surface transmission into a fuel bowser or via a fuel dispensing vehicle linked to a hydrant system directly into an aircraft and the fuel involved is near to water saturation, then excess water may condense out.
Other Petroleum Products -(eg MOGAS)
if a batch of aviation fuel is found to have been contaminated with another petroleum product to the extent that the specification requirements are no longer met then there is no remedy and the fuel concerned must be returned to a refinery for reprocessing. However, there are situations where very minor amounts of product mixing may occur without the specification being compromised but even here, if the contaminant is a surfactant , caution is required because the effect can be to degrade water separability. One contaminant which has been encountered in airport supply systems in recent years is Fatty Acid Methyl Ester (FAME) which is most likely to be found when biodiesel fuel has passed through a common unsegregated fuel distribution system.
Microbial growth - although aviation fuels are sterile when first produced, they inevitably become contaminated with micro-organisms that are omnipresent in both air and water Micro-organisms found in fuels include bacteria and fungi. Solids formed by microbial growth are very effective at plugging fuel filters and some micro-organisms also generate acidic by-products that can accelerate metal corrosion. Since most micro-organisms need (at least) free water to grow, microbial growth is most commonly found at any fuel-water interface that may exist. Higher ambient temperatures favour microbial growth. The most effective way to prevent microbial contamination is by minimising the presence of free water. The use of biocides may sometimes be an option if this type of contamination reaches problem levels, but their use is not necessarily an appropriate or complete response.