Civil Aircraft Advanced Avionics Architectures

Traditionally, the avionics architectures being implemented are of federated nature, which means that each avionics function has its own independent, dedicated fault-tolerant computing resources. Federated architecture has great advantage of inherent fault containment and at the same time envelops a potential risk of massive use of resources resulting in increase in weight, looming, cost and maintenance as well.

Reliable and timely transfer of data between avionics systems is a necessity in military and civil aircraft design. A powerful motivation for development of new data transmission systems has been the prolific growth in digital computing technology providing increasing opportunities for more modular, flexible and reliable avionics systems. This has resulted in a universal move from analog to digital data transmission and the emergence of the avionics data bus system. Over the last 30 years, much work has gone into exploring new techniques for the transmission of information in aircraft. ARINC 429 has emerged as a truly internationally recognized standard in the avionics industry.

Presently, Avionics plays an important role in civil aviation. The avionics functions are:

• To detect and process the data about environment inside and outside the aircraft
• To derive information in a form suitable for crew utilization
• To accept crew inputs and combine with other derived information
• To activate controls within the aircraft and simulate the outside environment as dictated by mission requirements of the system

As in other fields, digital computer systems have been incorporated in system aircraft avionics design. Digital avionics computers are coupled with multifunction displays with aircraft flight decks optimizing the man machine interface and enhancing the economy and safety of flight operations. This has resulted in modern digital avionics system to work in coordination, to function efficiently in terms of speed and capacity. Digital systems have better reliability, lower weight and greater flexibility for change or modification and potential for self-test function checks for faulty signals before takeoff. The need for rapid and automatic configuration is very much in case of a FLY BY WIRE (FBW) flight control systems (FCS) in which a faulty channel has to be switched out before it can jeopardize the safety of an aircraft.

The current day architecture of the latest avionics suite is based on the integrated approach, which is driven by the open architecture concept. With the drastic advancement in the computer and software technologies, the aviation industry is gradually moving towards the use of Integrated Modular Avionics (IMA) for civil transport aircraft, potentially leading to multiple avionics functions housed in each hardware platform. Integrated Modular Avionics is the most important concept of avionics architecture for the next generation of aircraft. IMA architecture includes several avionics functionalities combined in a single computer system with critically allocated resources for each functionality. Allocation of resource in IMA means the allocation of memory and CPU time for each avionics function which is critically done to avoid any fault propagation from one hosted function to the other. These mechanisms are governed by -established procedures and standards from Aeronautical Radio Inc (ARINC). The ARINC 653 relies on Integrated Modular Avionics.

Integrated Architecture has superseded the federated architecture in many ways with improved reliability, availability and redundancy. Integrated architecture has many advantages over federated architecture:

• Different levels of software in the same IMA box
• Reduction in the aircraft wiring length and hence reduction in weight
• Additions and modification of avionics functions are easy as it is software intensive functionality.

Integrated Modular Avionics (IMA) is a blanket term used to describe a distributed real-time computer network aboard an aircraft. This network consists of a number of computing modules capable of supporting numerous applications of differing safety criticality levels.

The Integrated Modular Avionics (IMA) concept, which replaces numerous separate processors and line replaceable units (LRU) with fewer, more centralized processing units, is promising significant weight reduction and maintenance savings in the new generation of commercial airliners.