SPZ--8000 Digital Integrated Flight Control System
A28--1146--055
REV 2
Troubleshooting
9-2
TROUBLESHOOTING DIGITAL AVIONICS
Maintenance of digital flight control systems requires a different
approach than that of analog systems. Crew members and
maintenance personnel can more effectively operate this digital system
by understanding the differences between it and analog systems.
Control law functions, once done with resistors, capacitors, coils, and
op amps, are now programmed digitally with microprocessors. Table
9--1 explains some of the differences between digital and analog
systems.
Digital System
Analog System
Digital flight control systems
repeat the same tasks with
identical results.
Over time, analog systems are
subject to component
degradation, that can influence
the outcome of the circuit’s
function.
Digital system self--tests are a
straight forward program check
during power application, as well
as during actual operations.
Analog system self-- tests are
complicated, typically involving
injecting signals and
measurement to determine their
effect. Therefore, most analog
systems are not equipped with a
self--test.
Digital systems produce event
codes that are used to
determine fault location.
Analog systems rarely diagnose
the cause of a fault or
intermittent event.
Digital systems are not affected
by temperature.
Analog systems are affected by
temperature extremes.
Digital and Analog System Differences
Table 9- -1
The nature of a digital system is, it works or it doesn’t. There are no
intermediate stages. An analog system can have many in--between
stages that can lead to confusion while troubleshooting. For example,
a digital system’s altitude preselect mode operates the same if pertinent
external sensor data is accurate. As time passes, an analog system
introduces variations to mode performance, even if its external sensors
have not yet changed.
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