Architecture Evolution

When avionics systems started to appear in the early twentieth century, there was little sharing of data or information between individual systems. Each system was self-contained and relied on the pilot to fuse data from different sources. For example, an aircraft may have a communication system, a navigation system, and a flight-control system but all three systems would operate independently. In fact, these early arrangements are called independent avionics architectures for this reason. Independent (analog) avionics is viewed as the first generation where each functional area had separate, dedicated sensors, processors and displays and the interconnect media was point-to-point wiring.

During the 1970s, data buses emerged as a method for transferring data from one computer to another over some distance. This technology found its way into universities, laboratories, and offices. It also found its way into aircraft where different avionics systems could communicate and share data along a common connection or bus. This freed the onboard computers to concentrate on their own tasks without a need to replicate the functions of other on-board systems. These arrangements are called federated avionics architectures and still dominate a large number of aircraft today. Federated avionics, the second generation, is typical of most military avionics flying today. Several standard data processors are often used to perform a variety of low-bandwidth functions such as navigation, weapon delivery, stores management and flight control. Low interconnect bandwidths and central control is possible because high speed signaling requirements such as A/D conversion and signal processing occurs within the "black boxes" through interconnections within dedicated backplanes in each of the federated chains. Use of these networks has dramatically simplified physical integration and retrofit problems.

This type of architecture was necessitated after the appearance of digital data processing on aircraft. The programmability and versatility of the digital processing resulted in the interconnectivity of aircraft state sensors along with avionic sensors which provide situation awareness and crew inputs. In contrast to analog avionics, data processing provided precise solutions over a large range of flight, weapon and sensor conditions.

The power of computers and the speeds of networks have continued to grow to an extent where a single avionics computer can perform a number of avionics functions concurrently. "Integrated avionics," which should really be called “integrated digital avionics”, makes up the third generation avionics architecture. It is typical of PAVE PILLAR-type avionics which was developed in the 1980s. The main feature of this architecture however, is the use of a small family of modular, line- replaceable units to accomplish virtually all the signal and data processing, arranged in conveniently located racks. The motivation behind this architecture was to simultaneously achieve several strides in avionics including the use of line replaceable modules, the elimination of the intermediate repair shop at the air base to reduce maintenance personnel, system reconfiguration down to the module level, cost reduction through the use of common, replicated modules, and the exploitation of blended data.

This architecture was needed to integrate affordable programmable signal processors into real-time avionic networks. Extraordinarily complex and expensive signal and graphic processors began to appear and unnecessary proliferation was occurring. Target, terrain and threat data from local sensors and stored data could be fused; new capabilities in situation awareness in which fused data was presented to the aircrew was now possible. A new, higher speed network was needed to "get at", fuse, and display this information. The concept of a small family of common signal processors thus emerged. From a performance perspective, the tight coupling of both signal and data computing assets allows new capabilities in data fusion to improve situation awareness.

The latest avionics architectures are building on the lessons learnt with integrated avionics architectures and are called advanced integrated avionics architectures. Fourth generation architectures, appropriate for consideration in the post-2005 time-frame, take the next step as we move towards the skin of the aircraft by integrating sensors within both the RF and EO domains to achieve a modular, line-replaceable design. Fundamentally, the same integration philosophy used in third generation digital systems is at work, particularly for the RF function. The identity of many radar, communications, and EW functions is lost from a hardware perspective. Functionality is achieved through software.