In some cases, aircraft must be defueled and then
refueled before flight operations can proceed.
When a fuel is found to be contaminated, the
contaminant must be tracked back to its source and
the cause corrected. Until the cause of the
contaminated system cannot be used. The fuel system
may be a mobile refueler, air station hydrant
refueling system, or the entire fuels system of an
aircraft carrier. Contaminated fuel may affect the
operation of one aircraft or the operation of an entire
air wing. For these reasons, be careful in every phase
of fuel handling to prevent contaminants from
entering the fuel.
CAUSES OF FUEL CONTAMINATION
How can you find out the causes of fuel
contamination? How can you find out how much
contamination is too much? Before you can determine
amounts of contamination, you have to be able to
understand the units of measurement used to identify
contamination. The two major units for measuring
the size of contaminants are microns for solids and
parts per million (ppm) for water.
There are approximately 25,400 microns in 1
inch. Figure 3-1 gives you 2 microscopic view of a
human hair, which is about 100 microns in diameter,
and compares it with a 5-micron contaminant.
Parts per million is the reference used for water
contamination. If you take a 32-oz sample bottle and
fill it 3 1/4 inches from the bottom, the amount you
will have is about 500 milliliters (ml). Break that 500
ml down into one million little pieces. You now have 1
As you now realize, the equipment used in the
quality surveillance laboratory has to be very
accurate to make measurements that small.
Operation of the lab equipment will be covered later
in this chapter.
Equipment now in use can remove most of the
contamination that may be present in a fuel. It
cannot separate two mixed or blended fuels. It cannot
effectively reduce the contamination below the
required limits if the contaminant level is too high.
YOU must be careful to prevent the introduction of
contamination in all phases of fuel handling.
Additionally, all steps of contamination removal
MUST be properly performed.
Inspection and sampling procedures are the only
means to ensure that the equipment is performing
properly. Unless the equipment is properly operated
and the sampling procedures are carefully followed,
the problem will always remain. Thus, the most
important factor in preventing and removing
contamination in fuels is the awareness of the people
who handle the fuel.
Figure 3-1.Enlargement of small particles and
comparison to a human hair.
The equipment is only a machine. You, the ABF,
the educated operator, make a quality surveillance
LIMITS OF CONTAMINATION
To be acceptable for delivery to aircraft, jet fuels
must be clean and bright. They must not contain
more than 5 ppm free water or 2 mg/liter particulate
contamination. The terms clean and bright have no
relation to the natural color of the fuel. Jet fuels are
not dyed and they vary from clear, water-white to
straw-yellow colored. Clean means the absence of any
cloud, emulsion, visible sediment, or free water.
Bright, means the fuel has a shiny, sparkling
A cloud, haze, specks of particulate matter, or
entrained water indicate that the fuel is unsuitable
and point to a probable breakdown in fuel handling
equipment or procedures. If contamination limits are
exceeded, delivery of fuel to aircraft shall be stopped
and corrective measures completed before resuming
CAUSES OF CONTAMINATION
Steps should be taken to find the source of
trouble and corrective measures taken immediately.
See figure 3-2 for the various types of contamination
that may be detected visually. The first sample of fuel
in this illustration is an acceptable fuel.
Water in fuels may be either fresh or salt and
may be present either as dissolved or free water.