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development of today’s highly technical avionics
systems? Modularity and COTS is important to
provide flexibility, growth potential and efficiency.
More and more the development
of avionics systems
requires extensive testing.
New generation aircraft,
such as the Boeing 7E7 and
Airbus A380, are to be fitted with specialized
systems that depend on
input/output (I/O) devices to control and
monitor various physical processes.
Such systems often must share data
with other avionics, using multiple heterogeneous
communications links.
Avionics Testing Process
Developing today’s avionics is a multifaceted
process that is made up of
numerous development cycles, effecting
both hardware and software. Each
cycle adds a new set of features to the
unit under test (UUT). And each feature
has to be validated through module
and system tests, to identify design and
implementation errors as soon in the
cycle as possible. As an avionics system
advances in its development certain
features may be simulated before
being implemented, to enable system
and integration tests.
These are the requirements that
test methodology must follow. Early
tests must simulate system interfaces,
while later tests must employ hardware
and software interconnections to
assure the system performs as expected.
Detecting errors in the early development
stage can cumulatively save
time and money. While modular testing
can be performed during a system’s
development, more comprehensive
system and integration testing must be
executed with the real target hardware.
Legacy test systems largely have
been built “from scratch,” then modified
and redesigned as a system’s
development progresses. They address
some testing needs but typically share
the following disadvantages:
➤ High cost/benefit ratio,
➤ Can conceal problems by reusing
in-flight system architectures for
testing purposes,
➤ Can hide costs in maintenance and
personal training,
➤ Provide limited flexibility, leading
to limited test system reuse, and
➤ Involve late testing cycles, missing
regression test capabilities.
Many times, with legacy test equipment,
test tasks can be missing—for
example, fault insertion at the hardware
and software level.
Advanced test equipment design—
made highly flexible, with a welldesigned
driver model—can shorten
the interval between UUT development
and integration, and thus save money.
The design must be able to allow for
building the test and integration rig in
parallel with the UUT’s development. In
other words, modern testing technology
must be able to easily grow with, and
swiftly adapt to, specifications that are
subject to change.
A large number of commercial offthe-
shelf (COTS) components should
be integrated to operate within the test
system. These include the standard aircraft
communications models, such as
avionics full duplex switched Ethernet
(AFDX), ARINC 429 and 717, Mil-Std-
1553, controller-area network (CAN),
serial RS232 and RS422, transmission
control or user datagram protocols
(TCP/UDP), among others. Whether
specifications are added, altered or
removed, the test rig must be adjusted
accordingly, with minimum effort.
Flexible test systems also should be
accompanied by a large catalog of lowand
high-precision analog and digital
hardware, with or without hardware
fault detection. For example, the catalog
should include TTL, digital, analogto-
digital converter (ADC), digital-toanalog
converter (DAC), rotary or linear
variable differential transformers
(RVDT/LVDT), function generators,
among others.
A highly specialized test system can
be built, cost-effectively, on top of a
generalized test system. However, the
generalized test system should include
the following features:
➤ An I/O system that addresses all
typical and atypical avionics hardware,
for example, communication
buses, digital and analog devices;
➤ COTS hardware components, to
benefit from the power of the realtime
equipment manufacturer
markets, as well as the longevity
and availability of products, which
play an essential role in obsolescence
management;
➤ High flexibility in signal wiring;
➤ Unified access to online data;
➤ A scalable real-time processing
engine that is able to run I/O and
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