Ultra-reliable real-time control systems-future trends

Today's aircraft use ultra-reliable real-time controls for demanding functions such as Fly-By-Wire (FBW) flight control. Future aircraft, spacecraft and other vehicles will require greater use of these types of controls for functions that currently are allowed to fail, fail to degraded operation, or require human intervention in response to failure. Fully automated and autonomous functions will require ultra-reliable control. But ultra-reliable systems are very expensive to design and require large amounts of on-board equipment. This paper will discuss how the use of low-cost sensors with digital outputs, digitally commanded fault-tolerant actuation devices and interconnecting networks of low-cost data buses offer the promise of more affordable ultra-reliable systems. Specific technologies and concepts to be discussed include low-cost automotive and industrial data buses, “smart” actuation devices with integral fault masking capabilities, management of redundant sensors, and the fault detection and diagnosis of the data network. The advantages of integrating the control and distribution of electrical power with the control system will be illustrated. The design, installation, and upgrade flexibility benefits provided by an all-digital and shared network approach will be presented. The economic benefits of systems that can operate following failure and without immediate repair will be reviewed. The inherent ability of these redundant systems to provide effective built-in test and self-diagnostics capabilities will be described. The challenges associated with developing ultra-reliable software for these systems and the difficulties associated with exhaustive verification testing will be presented as will additional development hurdles that must be overcome     

Design by extrapolation: an evaluation of fault tolerant avionics

Over the past 30 years, safety-critical avionics systems such as Fly-By-Wire (FBW) flight controls, full-authority digital engine controls, and other systems have been introduced on many commercial and military airplanes and spacecraft. Early FBW systems, such as on the F-16 and Airbus A320, were considered revolutionary and introduced with extreme caution. These early systems and their successors all make use of redundant and fault-tolerant avionics to provide the required dependability and safety, but have used significantly different architectures. This paper examines the different levels of criticality and fault tolerance required by different types of avionics systems, establishes architectural categories of fault-tolerant architectures, and identifies the discriminating features of the varied approaches. Examples of discriminators include the level of redundancy, methods of engaging backup systems, protection from software errors, and the use of dissimilar hardware and software. The strengths and weaknesses of the approaches will be identified. The paper concludes with some speculation on trends for future systems based on this evaluation of previous systems     

Flight-critical distributed systems: design considerations [avionics]

With the proliferation of so-called "smart" components and the availability of small, low-cost, and high-speed data networks, avionics that have traditionally been centralized are becoming distributed. A distributed approach offers many potential benefits, such as reduced development time and cost, simplified system installation, increased flexibility for system expansion or modifications, and greater reuse of proven components. The distributed approach can also reduce the risk associated with design errors by splitting complex hardware and software into more manageable components. However, distributed systems also introduce new challenges in meeting real-time deadlines and providing fault tolerance. This paper examines the many design considerations and identifies the strengths and weaknesses of each. Emerging automotive drive-by-wire alternatives are compared for application to aerospace systems. This paper is based on a Draper Laboratory-sponsored effort to look at flight-critical distributed systems and to evaluate emerging hardware and software for building them.