Many hydraulic units incorporate electrical
procedures are certainly adaptable to all aircraft main-
components to operate or control them. You must be
tenance, as well as other types of installations. Auto
able to determine if the electrical system is functioning
mechanics use these steps to find and repair malfunc-
normally; electrical malfunctions will usually be a
tions in automobiles. You will use the same procedure
complete power failure, circuit failure, or component
to find and repair malfunctions within aircraft systems.
Clarification of the seven distinct troubleshooting
4. Isolate the trouble. This step calls for sound
steps previously mentioned are as follows:
reasoning, a full and complete knowledge of hydraulic
1. Conduct a visual inspection. This inspection
theory, as well as a complete understanding of the
should be thorough and searching to include checking
affected hydraulic system. During this step, you must
all lines, units, mechanical linkage, and components for
use your knowledge and the known facts to determine
evidence of leaks, looseness, security, material
where the malfunction exists in the system. Usually the
condition, and proper installation. During this visual
trouble can be pinned down to one or two areas.
inspection, the hydraulic system should be checked for
Eliminating those units that could not cause the known
proper servicing, the reservoir for proper level, and
symptoms and those that can be proved to be operating
accumulators for specified preload, etc.
normally will usually identify the malfunction.
2. Conduct an operational check. The malfunc-
5. Locate the trouble. This step is used to
tioning system or subsystem is checked for proper
eliminate unnecessary parts removal, thus saving
operation. This is normally accomplished by attaching
money, valuable time, and man-hours. Often, you have
the support equipment to the aircraft, which supplies a
determined what unit or units in the system could have
source of electrical power and pressurized fluid to oper-
caused the malfunction, thus verifying the isolation
ate the hydraulic system. In some instances, however,
the aircraft may be ground checked by using aircraft
Both hydraulic and pneumatic malfunctions are
power and equipment. Whatever the case, during
verified in the same manner. You remove lines and
movement of the malfunctioning unit, the AM checks
inspect them for the correct flow in or at the suspected
for external leakage, the correct direction of component
unit. Internal leaks may occur in valves, actuators, or
movement, its proper sequence of operation, speed, and
other hydraulic units. Any unit that has a line that could
whether the complete cycle was obtained.
carry fluid to "return" is capable of internal leakage.
3. Classify the trouble. Malfunctions usually fall
Mechanical malfunctions are located by closely
into four basic categories--hydraulic, pneumatic,
observing the suspected unit to see if it is operating in
mechanical, or electrical. By using the information
accordance with the applicable aircraft MIM.
gained from steps 1 and 2, you, the AM, can determine
Mechanical discrepancies are usually located during
under which classification the malfunction occurs.
the visual inspection in step 1.
Something affecting normal flow of hydraulic fluid
Electrical malfunctions are located, with the
would be classified under the hydraulic classification.
assistance of AEs, by tracing electrical power
The flow of fluid may be affected by external and
requirements throughout the affected system.
internal leakage, total or partial restriction, or improper
6. Correct the trouble. This step is accomplished
only after the trouble has been definitely located and
Something affecting the normal flow of
there is no doubt that your diagnosis is correct.
compressed gases is classified as a pneumatic
Malfunctions are usually corrected by replacement of
malfunction. This type of malfunction stems from the
units or components, rigging and adjustments, and
same general sources as hydraulic malfunctions.
Most units that operate hydraulically or
pneumatically incorporate mechanical linkage. If a
NOTE: Always check the applicable MIM for
discrepancy in the linkage exists, it will affect the
CAUTION, WARNING, and SAFETY notes concern-
system's operation. Mechanical discrepancies should
ing maintenance procedures.
be found during visual inspections, and they are usually
7. Conduct a final operational check. The affected
in one of the following categories: worn linkages,
system must be actuated a minimum of five times, or
broken linkages, improperly adjusted linkages, or
until a thorough check has been made to determine that
improperly installed linkages.
its operation and adjustments are satisfactory.