Microbiological Contamination in Aircraft Fuel Tanks

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Sofema Online (SOL) looks at the issues.


Water and microbial contamination are issues of great concerns that are inherent to jet fuel. Certain bacteria and fungi are capable of existing in the water where it interfaces with the fuel. These microorganisms use alkanes and additives in fuel as foodstuff. These microbes can propagate rapidly.

If water is allowed to remain in fuel, it will culture micro-organisms or bacteria that feed on the hydrocarbons in the fuel, thereby degrading the fuel quality. Water can also promote corrosion in fuel system components.

Contaminated fuel can cause significant damage to the aircraft and engine. Damage can range from fuel system corrosion, clogging of fuel filtration components, failure of aircraft fuel system instrumentation, and even stopping the fuel supply to the engines during flight.

Bi Product of Bacteria & Fungi in Aircraft Fuel Tanks

The by-product is a sludge-like substance. In sufficient quantity, this can cause corrosion on steel and aluminum surfaces and attack rubber fuel system components. It can also foul filters and system instrumentation.

The most destructive of the microbes that grow in the aircraft fuel environment is the fungus Hormoconis resinae. One reason is because of its size.

Compared to single-cell yeasts and moulds, it produces far more biomass.

Reducing or Mitigating the Exposure

Elimination of water from the fuel system is one way to control microbial growth. In addition, there are additives such as Biobor that can be added to the fuel that can eliminate the growth of fungus and other microbes.

Products like these are soluble in both fuel and water.

How Does Water enter the Fuel System?

Jet fuel's composition allows water to be easily absorbed and held in suspension  Water can be present as suspended particles in the fuel and in liquid form. The amount of suspended particles varies with the temperature of the fuel.

Whenever the temperature of the fuel decreases, some of the water particles that are suspended in the fuel are drawn out of the solution and slowly accumulate at the bottom of the fuel cell. 

Whenever the temperature of the fuel increases, it draws moisture from the atmosphere to maintain a saturated solution. (Temperature changes will result in continuous accumulation of water.)

Potential Structural Damage

Microbiological contamination of fuels can also cause major problems for aircraft structure. The most common problems are corrosion of metallic structures, fuel quantity indication problems, blockade of scavenge system and fuel filters as well as sludge formation.

Monitoring & Testing

Aircraft fuel tanks must be routinely monitored for microbiological contamination.

Easicult Combi is for estimation of total bacterial count, as well as yeasts and moulds. Easicult M is for monitoring fungal contamination with its selective medium for yeasts and moulds. Easicult TTC is for easy detection of total bacterial count.

Tests are based on conventional colony-forming unit (CFU) method which is one of the IATA’s accepted methods for contamination monitoring. Both tests are reliable, easy to use, and suitable for airlines' field use.

Further Guidance

Sofema Aviation Services (SAS) and Sofema Online (SOL) provide training for aircraft inspectors delivered as classroom, webinar & online. 

For details please email office@sassofia.com or online@sassofia.com

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