Fuel suspected of microbiological contamination
contamination and correct it. Figure 4-3 shows
must not be defueled into a clean system.
an acceptable sample and common types of
contamination usually detected visually.
Sampling Procedures
WATER.-- Water in fuels is either fresh or
Fuel samples are taken from the fuel cell low-
saline and present as dissolved or free water.
Dissolved water is water in the fuel that is NOT
point drains as specified in the applicable
Maintenance Requirement Card (MRC) deck.
visible. Free water is a cloud, emulsion, droplets,
or gross amounts in the bottom of the container.
NOTE: Obtain fuel samples prior to
Any form of free water could result in icing,
refueling. Only trained personnel shall take
corrosion, or malfunctioning of fuel system parts.
fuel samples; personnel taking samples
Saline water will cause corrosion faster than fresh
must have clean hands. Improper con-
water.
tainers and poorly drawn or mishandled
samples result in meaningless or misleading
SEDIMENT.-- Sediment appears as dust,
results.
powder, fibrous material, grain, flakes, or stain.
Specks or granules of sediment indicate particles
1. Ensure exterior of low-point drain is
in the visible size (fig. 4-2) of about 40 microns
cleaned prior to sampling.
2. Drain off 1 pint from low-point drain,
or larger. In a clean sample of fuel, sediment
using a 1-quart, clear glass or polyethylene
should not be visible except upon the most
meticulous inspection. Sediment or solid con-
container.
tamination is either course or fine.
3. Inspect sample for loose drops of water
Course sediment is 10 microns or larger in size.
puddled under fuel.
Course particles can clog orifices and wedge in
NOTE: If dark stringy or fibrous material
sliding valve clearances and shoulders, causing
that tends to float in the fuel is noted in
malfunction and excessive wear. They can also
any sample, forward the sample(s) to the
clog nozzle screens and other fine filter screens
nearest Navy Petroleum Laboratory for
throughout the fuel system. Fine sediments are
microbiological growth determination.
less than 10 microns and are not visible as distinct
4. If water is detected, discard sample and
or separate particles. They appear as a dark
repeat steps 1 and 2 until no water is found.
shellac-like surface on sliding valves.
5. Swirl the sample by briskly rotating the
container.
MICROBIOLOGICAL
GROWTH.--
6. If water is present under the swirling
M i c r o b i o l o g i c a l growth consists of living
vortex, draw another sample and reinspect.
organisms that grow at a fuel/water interface.
7. Inspect fuel sample for any discoloration,
These organisms include protozoa, fungus, and
cloudiness, and loose sediment under the swirling
bacteria. Fungus is the major constituent causing
vortex.
many of the problems associated with biological
8. If small amounts of particulate material are
contamination of jet fuels. Fungus is a vegetable
noted, discard the sample, draw another sample,
life that holds rust and water. It is also a
and reinspect.
stabilizing agent for fuel-water emulsion.
9. If relatively large quantities of water or
Microbiological growth can develop wherever free
foreign matter are noted, or small amounts persist
water exists in the fuel tanks. Traces of metallic
from one or more cell drains, perform the
elements are also necessary, but water is the key
following:
ingredient. Remove free water and growth ceases.
a. Keep the fuel sample.
Microbiological growth is a brown, black, or gray
b. Immediately notify maintenance con-
color and has a stringy, fibrous-like appearance.
trol, who will ground the aircraft and notify the
It clings to glass and metal surfaces, causing
quality assurance division to perform an investiga-
problems such as severe corrosion or erratic
tion to determine the source of contamination.
operation of fuel system components. Micro-
c. If the source of contamination is not
biological growth causes erroneous readings in
isolated to the aircraft, notify the cognizant fuel
fuel quantity systems, sluggish fuel control
handling activity. The source of contamination
operation, and clogging of filters. It is more
must be identified. See table 4-1 for types of
prevalent in tropical and semitropical locations
contamination and limits.
because of higher temperatures and humidity.
4-7
