c. Fuels must be kept free of water to prevent plugging of the fuel system by ice crystals at high altitudes.
Elimination of water is also essential to prevent the growth of microbiological organisms. See MIL-HDBK-200, Chapter 9,
d. Turbine engine fuels, as well as AVGAS, form explosive mixtured readily. In order to Insure safety of personnel,
aircraft handling and refueling operations will conform to TM 10-1101, TM 10-1105 and FM 10-68.
a. 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 or JP-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% maximum.
Inhibitor, Icing, fuel system MIL-I27686, undiluted ethylene glycol monomethyl other is both
combustible and toxic. It is harmful If Inhaled or absorbed through the skin. It causes eye
Irritation. Before handling undiluted ethylene glycol monomethyl other, consult appropriate
safety and occupational health regulations.
b. 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. Refueling operations shall be accomplished in
accordance with accepted commercial procedures. (See specific aircraft manuals for any limitations.)
a. When changing from one type of authorized fuel to another, for example JP4 to JP-5, it is not necessary to drain
the aircraft fuel system before adding the new fuel.
b. Fuels having the same NATO code numbers are interchangeable.
c. Fuel controls and fuel flow dividers, that are adjustable externally on some engines may require retrimming or
readjustment for optimum performance when changing over to a fuel with a different specific gravity. The applicable
aircraft operating and maintenance instruction manuals should be consulted for additional information and procedures.
Occasionally, alternate fuels will be used in engines with fuel controls set for one specific fuel. Jet fuels conforming to
ASTM D1655 specification may be used when MIL-T-5624 fuels are not available. This usually occurs during cross
country flights where aircraft using NATO F-44 (JP-5) are refueled with NATO F-40 (JP-4) or commercial ASTM Type B
fuels. Whenever this condition occurs, the engine operating characteristics may change in the lower exhaust gas
temperatures (EGT). Slower acceleration, lower engine speed, easier starting, and shorter range may be experienced.
The reverse is true when changing from F-40 (JP-4) fuel to F-44 (JP-5) or commercial ASTM Type A-1 fuels. Specific
gravity adjustments in fuel controls and flow dividers shall be set for the type of fuel used. Most commercial turbine
engines will operate satisfactorily on either kerosine or JP-4 type fuel. However, the difference in specific gravity may
possibly require fuel control adjustments; if so, the recommendations of the manufacturers of the engine and airframe
are to be followed. Also, if the fuel quantity gage is calibrated in pounds, changing to fuels of different specific gravity
will cause the fuel gage to be in error.