FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 9. Aircraft Systems and Components | 2. Hydraulic Systems | 9-29. Hydraulic System Maintenance Practices
9/8/98
AC 43.13-1B
g. When handling Skydrol/Hyjet hy-
draulic fluids, gloves that are impervious to
the fluid must be worn. If skin contact occurs,
wash with soap and water.
h. When handling phosphate ester-
based fluid use eye protection. If the eye is
exposed to fluid, severe eye pain will occur.
i. When Skydrol/Hyjet mist or vapor
exposure is possible, a respirator capable of
removing organic vapors and mists must be
worn.
j. Ingestion of any hydraulic fluid
should be avoided. Although small amounts
do not appear to be highly hazardous, any sig
nificant amount should be tested in accordance
with manufacturer’s direction, followed with
hospital supervised stomach treatment.
tamination enters the system through normal
wear of components, by ingestion through ex
ternal seals, during servicing, or maintenance
when the system is opened to replace/repair
components, etc. To control the particulate
contamination in the system, filters are in
stalled in the pressure line, in the return line,
and in the pump case drain line of each system.
The filter rating is given in terms of “micron,”
and is an indication of the particle size that
will be filtered out. The replacement interval
of these filters is established by the manufac
turer and is included in the maintenance man
ual. However, in the absence of specific re
placement instructions, a recommended serv
ice life of the filter elements is:
Pressure filters3000 hrs.
Return Filters1500 hrs.
Case drain filters600 hrs.
9-29. HYDRAULIC SYSTEM MAINTE-
NANCE PRACTICES. The maintenance of
hydraulic and pneumatic systems should be
performed in accordance with the aircraft
manufacturer’s instructions. The following is
a summary of general practices followed when
dealing with hydraulic and pneumatic systems.
a. Service. The servicing of hydraulic and
pneumatic systems should be performed at the
intervals specified by the manufacturer. Some
components, such as hydraulic reservoirs, have
servicing information adjacent to the compo
nent. When servicing a hydraulic reservoir,
make certain to use the correct type of fluid.
Hydraulic fluid type can be identified by color
and smell; however, it is good practice to take
fluid from the original marked container and
then to check the fluid by color and smell for
verification. Fluid containers should always
be closed, except when fluid is being removed.
b. Contamination Control. Contamina
tion, both particulate and chemical, is detri
mental to the performance and life of compo
nents in the aircraft hydraulic system. Con
(1) When replacing filter elements, be
sure that there is no pressure on the filter bowl.
Protective clothing and a face shield must be
used to prevent fluid from contacting the eye.
Replace the element with one that has the
proper rating. After the filter element has been
replaced, the system must be pressure tested to
ensure that the sealing element in the filter as
sembly is intact.
(2) In the event of a major component
failure, such as a pump, consideration must be
given to replacing the system filter elements,
as well as the failed component. System filters
may also be equipped with differential pres
sure (∆P) indicators. These indicators are de
signed to “pop-up” when the pressure drop
across the element reaches a predetermined
value caused by contamination held by the
element. The indicators are designed to pre
vent false indications due to cold start, pump
ripple, and shock loads. Consequently, a filter
whose indicator has been activated must be re
placed. In fact, some indicator designs are
Par 9-28
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