Figure 3-9.—Installation diagram of a motor-driven hydraulic pump.
There are two classes of diagrams you will be
concerned with in gaining a complete knowledge of a
specific system. These are the schematic and installation
diagrams. A diagram, whether it is a schematic diagram
or an installation diagram, maybe defined as a graphic
representation of an assembly or system.
Schematic Diagrams
Figure 3-8 is another example of a schematic
diagram. Diagrams of this type do not indicate the actual
physical location of the individual components in the
aircraft. They do locate components with respect to each
other within the system. Various components are
indicated by symbols in schematic diagrams, while
drawings of the actual components are used in the
installation (pictorial) diagrams. The symbols used in
the schematic diagrams conform to the military standard
mechanical symbols provided in MIL-STD-17B-1 and
MIL-STD-17B-2. Most manufacturers improve upon
these basic symbols by showing a cutaway portion on
each component. These cutaways aid in clarifying the
operation of that component. You should be able to trace
the flow of fluid from component to component. On
most diagrams of this type, an uncolored legend or
different colors are used to represent the various lines.
The legend identifies the lines in relation to their purpose
and the mode of operation being represented. Each
component is further identified by name, and its location
within the system can be determined by noting which
lines lead into and out of the component.
Since many systems are electrically controlled, you
should be capable of reading the electrical portion of a
schematic diagram. Knowledge of the electrical
symbols and the use of a multimeter in making voltage
and continuity checks will contribute significantly to
efficient troubleshooting. If a malfunction is caused by
electrical problems, the assistance of AE personnel may
be required.
All electrical wiring in the aircraft is marked at
specified intervals with a wire identification code. These
identification codes are defined in the electrical
volume(s) of the MIM, and they are useful in tracing
wires throughout the aircraft. If an elusive malfunction
is reasonably traced to or considered to be of an
electrical nature, the electrical circuit should be checked
by a qualified AE. Many wires can give a good
continuity reading under a no-load or low-current
condition and still be malfunctioning when under a load
condition.
NOTE: Electrical schematics are especially
useful in determining annunciator panel
malfunctions.
Installation Diagrams
Figure 3-9 is an example of an installation diagram.
This is a diagram of the motor-driven hydraulic pump
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