Malfunctions Caused by Air.
In general, all components and
systems that do not require gases in their operation are to some
extent impaired by the presence of air.
Examples are excessive
feedback of loud noises from flight controls during operation, and
the failure of wheel and rotor brakes to hold.
can be readily corrected by "bleeding the system": a controlled way
of allowing the air to escape. The process is explained in detail in
the -20 TMs of the particular aircraft involved.
Two general types of fluids can be used in the operation and
maintenance of hydraulic systems and equipment: vegetable-base and
mineral-base. Although both types of fluids possess characteristics
suitable for hydraulic use, they are not interchangeable, nor are
they compatible as mixtures.
At present, only mineral base fluids
are used for the maintenance and operation of hydraulic systems and
self-contained hydraulic components of Army aircraft.
vegetable-base hydraulic fluids cannot be left entirely out of this
In the past, some Army aircraft have used vegetable-base fluids for
hydraulic system maintenance and operation.
Also, all known brake
systems in automotive vehicles are currently being operated on
It is quite possible that a supply of this
type of fluid may erroneously fall into the aviation supply system.
Therefore, maintenance personnel must be familiar with both types of
fluids so they can recognize the error and avoid use of the improper
Moreover, knowledge of the effects of using the improper
fluid and the corrective action to take if this occurs is as
important as knowledge of the system itself.
Rubber parts of hydraulic systems are particularly sensitive to
The rubber parts used in systems operating on
vegetable-base fluids are made of natural rubber; those operating on
mineral-base fluids are made of synthetic rubber.
Both types of
rubber are seriously damaged by contact with the wrong type of fluid.
Vegetable-Base Hydraulic Fluids. Vegetable-base hydraulic fluids
are composed essentially of castor oil and alcohol.
have an easily recognized pungent odor, suggestive of their alcohol
There are two types of vegetable-base hydraulic fluids that
aviation personnel can be issued in error; aircraft and automotive
types. Their descriptions follow: