Petroleum-base fluid MIL-H-6083. MIL-H-6083 is still authorized for certain uses in Army aircraft. It is
used as a preservative oil in shock struts, hydraulic equipment, and spare parts, and as a testing and flushing oil for
some components. It should not be used in operational aircraft hydraulic systems.
Petroleum-base fluid MIL-H-5606. MIL-H-5606 is being phased out for most Army aircraft, and being
replaced with synthetic-base fluid MIL-H-83282. It is, however, still used for cold weather operation. Refer to the
following paragraph and paragraph 4-21 for more information on this fluid and its conversion.
Synthetic-Base Fluid MIL-H-83282. As stated above, MIL-H-5606 is being replaced in most operations by
MIL-H-83282. MIL-H-83282 has a higher flash point and fire point, as well as additives which provide better anti-wear
characteristics and provide better resistance to corrosion and oxidation. Refer to paragraph 4-21 for more information on
this fluid and its conversion.
Precautions. Use of the correct, uncontaminated fluid in a particular hydraulic system is critical for the
continued serviceability of that system.
Proper fluid. You must be extremely careful to use only the fluid authorized for a particular component
or system. To determine the correct fluid, consult the applicable technical manual. In addition, read the instruction plate
affixed to the individual unit or reservoir and check the color of the fluid contained in the system.
Drained fluid. Fluid drained, for any reason, from a hydraulic system or component shall not be
Disposition of containers. Hydraulic fluid containers, when emptied, shall be destroyed.
Fluid Contamination. Contamination in a hydraulic system is the presence of any material other than the
hydraulic fluid being used. This includes water, metal, dust, and other solids. Contamination sources may be internal or
external. Internal contamination can cause abnormal wear of the pump or of other components. When filters are used
too long (especially the paper element type), particles may begin breaking off from the filter element. Moving seals and
backup rings also add contamination to the system. External contamination is generally caused by poor maintenance
practices. Examples include leaving hydraulic lines open after removing a part, wiping fittings with dirty rags; leaving
valves, tubing, etc , uncovered on workbenches; changing fluid with dirty test equipment, and installing new or rebuilt
parts that have not been properly cleaned Hydraulic fluid (red color), MIL-H-83282 or MIL-H-5606, shall be used in all
hydraulic systems The choice of MIL-H-83282 or MIL-H-5606 depends on the particular hydraulic system and the
ambient temperature Refer to the aircraft manual or to TB 55-1500-334-25.
Detecting Fluid Contamination. A kit has been developed, part number 57L414, NSN 6630-00-150-6486, to
sample fluid for contamination in order to help control contamination in aircraft. Contamination checks should become a
routine part of your work. You should check for dirt, metal, and visible solids every time a unit is removed or
disassembled. Normal contamination checks for most aircraft are made by examining the condition of the filter
elements. For example, a clogged filter or an extended filter indicator pin is a symptom of contaminated fluid. These
findings, as well as a pump failure, require flushing of the system.
System Flushing. Evidence of contamination makes it necessary that hydraulic system be flushed.
To avoid contamination, do not use hydraulic fluid that shows evidence of contamination or is in open cans
that are stored uncovered/unprotected. Unused fluid may be kept in filler pumps or sealed jars.
Fluid. Hydraulic fluid, MIL-H-5606 or MIL-H-83282, shall be used for flushing systems and
components. Discard after use.
Accidental servicing. In the event that a system or component Is Inadvertently serviced with incorrect
type fluid, drain fluid, flush system, and replace all packings and gaskets in affected components.
Contamination Prevention. Contamination can be prevented by taking the following precautions.
Cap or plug all open connections when removing a part.
Never use dirty rags to wipe off connections.