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 contamination is found and corrected, 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 ppm. 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. HUMAN FACTOR 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 program work. 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 appearance. 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 fueling operations. 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 Water  in  fuels  may  be  either  fresh  or  salt  and may  be  present  either  as  dissolved  or  free  water. Dissolved 3-6