Table 2-3. Visual Contaminant Characteristics - CONT
Emulsions - continued
Fuel and water or
Reddish, brownish, grayish,
Finely divided drops of fuel in
Sticky material water. Contains rust or micro-
variously described as
biological growth which stab-
lizes or firms-up the emulsion.
Will adhere to many materials
normally in contact with fuels.
Usually present as globules or
stringy, fibrous-like material in
clear or cloudy fuel. Will stand
from days to months without
separating. This material con-
tains half to three-fourths water,
a small amount of fine rust or
microbiological growth and is
one third to one half fuel.
Lacy bubbles or scum at
Extremely complicated chemi-
interface between fuel and
cally. Occurs only when emul-
water. Sometimes resembles
sion and free water is present.
Cloud in fuel.
Disperses upward within a
Specks in fuel.
Float on top, within fuel, or
settles to bottom.
Figure 2-2. Micron Particle Size
Microbiological Growths. Microbiological growth
is growth of living organisms (protozoa, fungi, or bacteria)
at the interface between fuel and water wherever there
are pockets of water in fuel tanks. If there is no water in
the fuel, microbes cannot grow. The growth is brown,
black, or gray and looks stringy or fibrous. Microbiological
growth contaminates fuel and causes problems because
the organisms hold rust and water suspended in the fuel
and act as stabilizing agents for fuel/water emulsions.
These suspensions cling to glass and metal and can
cause false, fuel-quantity readings. They also make fuel
controls operate sluggishly and make fuel flow-dividers
stick. Microbiological growth in aircraft fuel is a reliable
indication that the fuel filters have failed, that the water
has not been properly stripped from the fuel, or that the
fuel storage tanks need to be cleaned more frequently.