Contamination of Fluids Used in Aviation Industry

Safety is of critical importance in the aviation industry. If there is poor safety management in any company involved in aviation, not only it results in delayed flight operations at a substantial financial loss but it can also result in accidents that may cause damage to the aircraft and injury or death of its passengers.

Aircraft systems use a wide variety of fluids, some of which are critical to flight operations. Landing gear, flaps, brakes, etc., all operate on hydraulic systems. Similarly, many GSEs use oils and lubricants which are essential in their operations. Jacks, lifts, cranes, and various service vehicles all have hydraulic-based systems. These fluids include fuel for the aircraft and vehicles, oil for lubrication, water for cooling/cleaning, and other oils and fluids used in hydraulic systems.

Contamination in Hydraulic Fluids

Contamination in hydraulic fluids can have serious adverse effects on the fluid’s physical and chemical properties. The loss of crucial fluid properties, which are central to useful service life, can result in inefficient system performance and leads to faster mechanical wear and tear of the components of the hydraulic systems.

Hydraulic fluids are comprised of base stock and some chemical compounds designed to protect the oil as well as the components in the hydraulic systems. They also ensure the optimum performance of the systems. Typical additives include dispersants, antioxidants, detergents, anti-corrosion, anti-foaming agents, and viscosity retainers.

Particulate Contamination

Dirt and dust particles can make their way into the hydraulic system from the outside and cause contamination of the fluid. This may be sand, mud, metal powder, or pretty much any small bits of matter that makes its way into the fluid reservoir. Most of the particles are produced when a hydraulic system is manufactured, and later, during operation as the components wear off, but they can also be ingested during equipment maintenance when the system is open for repair. It can also get inside the hydraulic system via leaking seals.

If fluids can leak out, the contamination can get in. To prevent this type of contamination the hydraulic system should be opened only in a clean environment. Also, the equipment should be cleaned before opening it up so nothing falls inside the hydraulic system during maintenance.

Contamination particles in the presence of water form insoluble precipitates and viscous gels. These materials induce excessive stress on system components mainly pumps as they clog nozzles, orifices, and jets.

Water Contamination in Hydraulic Fluid

If the hydraulic fluid looks milky-white, then it is quite likely contaminated with water. Water contamination reduces fluid viscosity, increases oxidation rate. It affects compressibility and can cause increased corrosion. It also reduces the effectiveness of the hydraulic fluid to act as a lubricant. It also helps to form sludge which can lead to damage to the hydraulic pump and result in its eventual failure.

In extremely cold weather water in the system turns to ice, while the machine is not working overnight. Ice can restrict fluid flow during start-up and cause cavitation in the suction line. It will degrade system performance, can produce malfunctions, and damage the system.

Ingress of Air

If the hydraulic fluid looks foamy then it is quite likely that it is contaminated with air. Air trapped in hydraulic pathways will affect its compressibility and thereby reduce the performance of the system. To minimize this contamination, avoid exposing the hydraulic system to air.

Chemical Contamination

Another common type of hydraulic contamination is chemical. One of the primary causes of chemical contamination is the natural degradation of the hydraulic fluid. Over time, the chemicals that make up the fluid break down into components, and those components are not good for the hydraulic system. Excessive heat can speed up this process.

If two different hydraulic fluids are mixed, then it is possible that their additives may not be compatible and react chemically to produce chemical contamination. This is the main reason why one should not mix different types of hydraulic fluids. Hydraulic fluid has a finite useful life and will degrade with time. Change the hydraulic fluid as per the manufacturer’s recommendation.

Contaminated hydraulic fluid is a serious issue for your equipment. It can reduce efficiency, and lead to damage and failure. To avoid this happening make sure to change the filters as per routine to keep the hydraulic fluid clean.

Contamination in Aircraft Fuel

Fuel contamination can be very expensive in the aviation business. Jet fuel contamination can keep a commercial aircraft grounded for weeks for cleaning and checking. If gone undetected it can lead to aircraft accidents. Therefore it is critical to detect contamination early and fix it immediately. The most common contaminants in fuel are particulates, water, other petroleum products, and microbial growth:

Microbial Growth

Any type of fuel contamination can affect the quality of aviation fuel, but microbiological contamination is particularly serious with stored fuel. The danger posed depends on the type of organism, the fuel itself, and any additives used. Microorganisms include bacteria and other fungi, including some type of yeasts. This type of contamination can degrade the fuel quality significantly.

Particulate Contamination

The interior surfaces of fuel tanks and pipes have protective coatings, but still, the metals generate rust and corrosion particles that contaminate the fuel. Even small quantities of water in the fuel distribution systems will lead to the development of rust which will eventually contaminate the fuel.

Other airborne particles like dust, sand, rubber, paper, and fabric particles can enter the fuel tanks and pipes. Some particulates can be checked visually while other smaller particulates can be detected by chemical analysis.

Water Contamination

Aviation fuel often gets contaminated by water while it is transported and stored until it is pumped into the aircraft tanks. Water can come from rain or snow and moisture from the humid air.  The water may leak in through seals of valves, pipes, and tanks. Air moving in and out of a tank while fuel is being loaded and unloaded may also change the moisture content of the air in contact with fuel, which can result in water contamination of the fuel.

Water contamination in aviation aircraft fuel can be detected in many different ways. There are many other products and analysis equipment commercially available that can test for jet fuel water contamination. The maximum allowable limit of water in fuel is 30 ppm.

Contamination with other Petroleum Product

If aviation fuel is contaminated with another petroleum product or with a fuel of different specifications then the fuel must be removed from the aircraft. The fuel tanks should be flushed and filled with correct specification fuel.

Avoiding Fluid Contamination

Contamination of any fluid in the aviation industry is very serious and it must be ensured that these fluids are clean, meet the required specifications and remain clean throughout their service life. Routine testing is essential as part of the preventive maintenance routine. If any fluid is found to be out of specifications, then it should be flushed out, and the fuel tank cleaned before replacing it with new fluid, following the specific protocol for that system.

Standard operating procedures should be used to restrict fluid contamination. The procedures should be in place to ensure to keep contaminants from entering the system.

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