MIL-DTL-24784/19B (SH)
logic diagrams and text may be used. If functional explanations are needed to support the
procedures, specific references shall be made to the functional description rather than repeating
such material.
3.6.9.1 Section 1 - Indicator fault directory. This directory shall relate system fault indications
encountered during normal operation or system exercises to the most appropriate documentation
for isolation of faults shown by each indicator. The directory shall be presented in tabular form
with the system fault indicators arranged by operational modes and by pertinent equipment for
each mode, by cross-referencing from equipment output functions in an FLD or an SFD. Every
applicable equipment output that is required for system operation shall be listed (see figure
19-10).
3.6.9.2 Section 2 - System fault-isolation procedures. Fault-isolation procedures shall be
developed for fault indications observed during system operation or system tests that cannot easily
be isolated using the SFD. The procedures should be in the form of FLD, but can be in the form
of narrative text or a combination of diagrams and text. Functional descriptions in the description
and operation portion of this manual type shall be referred to, as needed, rather than being
repeated. This portion shall explain the use of the FLD in terms of relationship and use with other
system maintenance documentation. Each FLD shall be preceded by an explanatory description of
the isolation procedure involved. This description shall include mention of the functions or
conditions leading up to and influencing the initial element of the isolation procedure.
3.6.9.3 System fault logic and troubleshooting-maintenance dependency-matrix diagrams.
System FLDs shall be prepared for fault indications observed during either scheduled tests or
operation. These diagrams shall isolate the functional area of the equipment at fault and then refer
the user to the equipment technical manual containing the information needed to complete the
fault-isolation and repair. Each diagram shall include or make reference to information necessary
to establish the system test or operating conditions required for starting the fault-isolation
procedure. The conclusion boxes shall list the equipment or functional area within a equipment
that is the probable source of malfunction and the technical manual reference or references for
further isolation and repair of the fault. Troubleshooting-matrix diagrams in accordance with
MIL-DTL-24784 may be substituted for or augment FLDs.
3.6.10 Chapter 9 - SFDs. SFDs shall be developed to provide complete coverage of a system in
all modes of operation (see figure 19-11). They are to serve as illustrations supporting the
detailed functional description and as system troubleshooting reference drawings. Each diagram
shall show the generation, transmission, switching, and use of one or more functions on a system
basis. An SFD shall show signal flow across equipment interfaces and include those circuits that
significantly modify the signal. One-lining, which is the superimposition of two or more wires or
circuit elements, shall be used where no loss of clarity is involved. All test points needed for
system troubleshooting and all devices such as dials and indicators that are monitored during
system testing shall be shown. The correct voltage, waveform, reading, or other condition for
each shall be indicated as appropriate. When space on the diagram is insufficient, particularly in
the case of test point data for multiple problems or setups of a system test, these data may be
provided on associated tabulation sheets. Wiring tabulation sheets that are keyed to the diagrams
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