Download Integrated Modular Avionics for Space Applications

Chapter 2
Aeronautical Avionic Systems
In this chapter the current state of the art avionic system will be discussed. I will describe this system
from a historical perspective explaining briefly the evolution that avionic systems took to their current
state. Several underlying concepts to the avionics platform will be presented.
2.1
Historical perspective
Avionics is a term used to describe electronic systems used in aviation. The word itself is result of a
blend between the words “aviation” and “electronics”. The first use of electronic equipment in aircraft
dates back to the Second World War, where simple radars and radios were incorporated in military
aircraft. Since then the number and complexity of avionic systems has grown exponentially.
From its origin to the end of the twentieth century the avionics development has followed a federated
architecture. In this architecture each function of the avionic system is a self contained black box that
includes every resource needed for it to achieve its functionality. This black box, a Line Replaceable Unit,
contains all the Hardware, Software and interfaces required for that function. The system integrator
is unaware of the inside structure of the LRU, because its development is usually performed by an
independent contractor [1].
The self-contained nature of the LRUs allows them to be modular and quickly replaceable at an operating location. This modularity decreases maintenance costs since a damaged LRU can be replaced
quickly by a new stocked one. Furthermore a LRU ensures fault containment given that a falling unit will
just stop providing its function and will not affect others. LRUs are designed following a set of standards,
mainly ARINC specifications, which specify their interfaces and physical characteristics. Several manufacturers and military organization have also defined their own proprietary standards. Figure 2.1 depicts
an Line Replaceable Unit.
As the number of functions required by an aircraft started growing, the shortcomings of the Federated
Architecture became self-evident. Each new function will add a new LRU to the aircraft, requiring more
power, mass, and volume from the aircraft. This direct correlation between number of functions and
the mass/power consumption enforces aircrafts with high number of functions to be impractical [1]. The
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