Areonautica Civil

All hydrocarbon fuels contain some dissolved and suspended water.
the quantity of water contained in the fuel depends upon the temperature and type of fuel, with its higher aromatic content, tendsto absorb and suspend more water than aviation gasoline. Along with the water, it will suspend rust, lint and other foreign materials longer. Given sufficient time, these contaminants will settle tothe bottom of the tank. However, the settling time for jet fuel is five times that of aviation gasoline. Due to this fact, jet fuels require good fuel handling practices to ensure that the airplane isserviced with clean fuel. If recommended ground procedures are carefully followed, solid contaminants will settle to the bottom of the fuel cell and free water can be reduced to 30 parts per million(ppm) a value that is currently accepted by major airlines.
Since most suspended materials can be removed from the fuel by sufficient settling time and proper filtration, they are not a major problem.Dissolved water has been found to be major fuel contamination problem. its effects are multiplied in airplanes operated primarily in humid regions and warm climates.
Dissolved water cannot beremoved from the jet fuel by micronic filters, but can be released by lowering the fuel temperature, such as will occur in flight. For example a jet fuel may contain 65 ppm ( 8 ounces per 1000 gallons) ofdissolved water at 80º F. When the fuel temperature is lowered to 14º F, only about 25 ppm will remain in solution. The difference of 40 ppm will have been released as supercooled water dropletswhich need only a piece of solid contaminant or and impact shock to convert them to ice crystals. Test indicate that these water droplets will not settle during flight and are pumped freely throughthe system. If they become ice crystals in the tank, they will not settle since the specific gravity of ice is approximately equal to that of jet fuel. Although 40 ppm of suspended water seems like...