TM 1-1500-204-23-3 d.    Uses  of  Additives  to  Prevent  Mirobiological  Growth. The   addition   of   fuel   system   icing   inhibitor   (FSII)   has helped curb microbiological growth. However,  in  spite  of  the  effectiveness  of  FSII,  it  is  still very important to remove all water from aviation fuel and aircraft fuel systems. (1)  Oxidation and corrosion inhibitors.  In general, ASTM specifications   for   jet   fuels   permit   the   use   of   approved oxidation and corrosion inhibitors and metal deactivators. However, the quantities and types must be declared and agreed to by the consumer.  Military specifications permit use of a metal deactivator in either JP-4 orJP-5 fuel and also   permit   an   approved   corrosion   inhibitor   in   JP-4, provided it is blended into the fuel by the supplier.  MIL-T- 5624  presently  contains  the  requirement  that  both  grade JP-4  and  JP-5  contain  icing  inhibitors.    The  specification requires that these inhibitors be added at the refinery to a minimum    percent    volume    of    0.10    and    0.15    percent maximum. (2)  Icing  inhibitor.    Icing  inhibitor  conforming  to  MIL-1- 27686  shall  be  added  to  commercial  fuel  not  containing an icing inhibitor during refueling operations, regardless of ambient  temperatures.    The  additive  provides  anti-icing protection and also functions as a biocide to kill microbial growths  in  aircraft  fuel  systems.    The  additive  (Prist  or equivalent)   is   not   available   through   the   Army   Supply System    it    is    to    be    procured    locally    when    needed. Refueling operations shall be accomplished in accordance with accepted commercial procedures. (See specific aircraft manuals for any limitations.) e. Contamination    Prevention.        Any    time    fuel    is transferred,    it    is    susceptible    to    contamination.        The following  paragraphs  contain  precautions  to  prevent  fuel contamination. (1) Fuel   storage.      Fuel   being   pumped   into airpiort   storage   should   pass   through   a   filter-separator. The     filter     should     meet     the     requirements     of     U.S. Government Specification MIL-F-8508A. (2) Turbine    fuel.        Turbine    fuels    should    be allowed to settle for a period of one hour per foot of depth of  the  fuel  before  being  withdrawn  for  use.    This  means that   ordinarily   more   than   one   storage   tank   must   be provided for each grade of product. (3) Storage   tanks.      Storage   tanks   should   be checked  with  litmus  paper  after  each  new  load  of  fuel  is received   and   the   fuel   has   settled.      The   litmus   paper should remain submerged for a minimum of 15 seconds.   During  periods  of  heavy  rain,  underground  tanks  should be checked with litmus paper more frequently. (4) Suction  lines.    Suction  lines  should  be  a minimum   of   6   inches   from,   the   bottom   of   the   tank. Kerosene storage tanks should be equipped with floating type suction lines.  Floating suction does not remove the bottom  product,  which  may  not  have  settled  sufficiently. It    also    prevents    reintroduction    into    the    fuel    of    any contamination at the bottom of the tank.  Floating suction is the only logical way to take full advantage of gravity in removing water and particulate matter contamination.  Its importance must not be minimized. (5) Fuel   withdrawal.      Fuel   being   withdrawn from  storage  should  be  passed  through  a  filter  separator meeting the specification MIL-F-8508A. (6) Loading.  Great care should be exercised in loading  mobile  fuelers  to  exclude  airborne  dust  and  dirt, rain or other foreign material. (7) Tanks.  To lessen the likelihood of rust and scale the tanks of mobile fuelers should be constructed of either stainless steel, nonferrous material or steel coated with a reliable, inert material. (8) Filtering.  As turbine fuel is being dispensed into the aircraft from truck or hydrant it should be filtered to a degree of 5 microns for solid particles and contain no more  than  0.0015  percent  of  free  and  entrained  water. Bypass valves around the filter should not be permitted. (9)  Quality    control.        All    the    quality    control procedures    usually    followed    in    handling aviation     gasoline     should     be     employed. These include regular and frequent check of filter-separators; frequent quality check such as  the  clear  and  bright  test.    and  continual emphasis on cleanliness.  Examples: "Don't let   the   hose   nozzle   drag   on   the   apron." "Keep the dust cap on the nozzle at all times when nozzle is not in use." 2-5.  Fuel System Maintenance.    General  maintenance on   fuel   lines,   pumps,   sumps,   strainers,   float   switches, cells, tanks, quick-disconnect couplings, and closed-circuit refueling    receptacles    are    explained    in    the    following paragraphs.  Fuel system testing and troubleshooting are also  covered.    Inspection,  removal,  and  installation  are covered in TM 1-1500-204-23-2. a. Fuel    Lines.        Various    fuel    tanks    and    other components   are   usually   joined   together   by   fuel   lines made  of  metal,  connected  where  flexibility  is  necessary, by lengths of flexible hose.  Metal and flexible hose lines and  inspection,  removal,  and  installation  of  fuel  lines  on aircraft are explained in the following paragraphs. 2-6