and recognize normal readings. Learn how to use
These errors may result from faulty procedures
test equipment and read schematics before you
or by the way you think about your work. A
are required to troubleshoot a problem.
report entitled "A Preliminary Investigation of
Troubleshooting" lists common troubleshooting
practices to avoid. The report indicates that you
should avoid making the following common
USE OF DIAGRAMS, DRAWINGS, AND
CHARTS IN TROUBLESHOOTING
1. Checking parts of the system that had
The diligent use of the applicable maintenance
nothing to do with the cause of the symptom.
instruction manual (MIM) is essential in pre-
2. Ignoring part of a system because you
venting poor troubleshooting procedures. The
MIM for each aircraft provides troubleshooting
didn't know that the unit was a possible cause of
aids that cover the six steps listed in the previous
section. These manuals provide a variety of
troubleshooting aids. Table 9-2 shows examples
3. Making a difficult check when a simple one
would have done the job.
of troubleshooting chart formats. These charts list
a definite sequence of action for a problem,
4. After isolating the engine trouble between
of investigation. These charts supply the trouble,
two points, making further checks beyond,
probable cause, and the remedy for some of the
rather than between these points. Sometimes
more common malfunctions.
making a check between two points despite
the fact that no engine trouble was found between
The MIM also contains schematics and
diagrams for use in troubleshooting. Diagrams
of the various electrical circuits, fuel systems,
5. Omitting a check even though you know
it is related to the situation.
and lubrication systems are very useful in
isolating discrepancies. There are many types
of diagrams, but those most important for
6. Attempting to remember a lot of informa-
troubleshooting include schematics and pictorials.
tion, This finding points out the necessity of
There are some MIMs that combine different
writing down all information during checks, and
using the maintenance manuals, not your
types of diagrams to provide more information.
To understand how a system or component of the
aircraft functions, you must be able to read these
The report pointed out that troubleshooters
sometimes made errors because of previous
Schematic diagrams enable maintenance per-
experience in similar situations. When they
sonnel to trace the path of electrical circuits, fuel
analyze and repair the engine trouble success-
systems, and lubrication systems of aircraft.
fully, they have a feeling of satisfaction.
Schematic diagrams use symbols for a graphic
They then tend to use the same procedures,
representation of the assembly or system.
even though the procedures are not relevant
Electrical components or circuits use the standard
to the present engine trouble. Similarly, if
electrical symbols shown in figure 9-1. Look at
the mechanic tried certain checks in the past
this figure and notice the electrical symbols for
and they did not fix the problem, the mechanic
FUSE, SPLICE, GROUND, and POLARITY.
was reluctant to use them again, even when they
Some of the mechanical symbols used in
provided required information to correct the
schematics are shown in table 9-3. A complete
listing can be found in the Military Standard,
Mechanical Symbols for Aeronautical, Aerospace,
To become an expert troubleshooter, you must
and Spacecraft Use, Part 2, MIL-STD-17B-2.
know the function of each part and how the
operation of one part or system affects another.
Schematic diagrams show the relationship of
A good way to learn engine systems and the
different relationships is to study schematics and
each part with other parts in the system. They do
not always indicate the physical location of the
diagrams. Trace out all the systems you work on,