Flight is one of the miracles of modern life. It has made the world a smaller place, allowed human beings to travel from one side of the Earth to another in less than 24 hours, and helped usher in an integrated, globally connected economy. It’s also an essential component of military activity around the world. Such complex and expensive machines require sophisticated safety-critical embedded systems in order to function properly. In this article, we’ll explain how these systems are put to work in aviation applications.
Safety-Critical Embedded Systems Explained
This is a pretty loaded term so let’s dissect what all these words mean. When you hear a system described as “embedded” it means that is consists of a combination of software and hardware which forms a part of a larger system. Basically, it operates as a component of the larger system and performs one or more specific functions to help that larger system function as intended. For example, a microprocessor within a cell phone would be considered an embedded system.
Not all embedded systems are considered safety-critical, however. Safety-critical embedded systems are systems that could result in damage to property, physical injury or death if they were to malfunction or fail. One obvious example would be the braking system in an automobile.
Since systems can be embedded within each other, a failure in one system can trigger a "failure avalanche" and ultimately, system-wide failure. If a particular component of an embedded system is defective or doesn’t always function properly, it is considered a fault. A fault may or may not manifest itself as an error (a strange or unexpected behavior) and an error could end up triggering a failure, which is when the embedded system doesn’t perform properly at all. When this occurs with a safety-critical embedded system, you could have a potentially life-threatening situation on your hands.
Understanding Safety-Critical Embedded Systems and Avionics
All motorized vehicles have safety-critical embedded systems, and perhaps no other type of travel is as dependent upon them as aviation. Whether it’s a UAV worth millions of dollars, a stealth bomber, or a 747 with four hundred passengers on board, the margin for error is VERY small when you are thousands of feet in the air, and the margin for outright failure is almost nil.
Just a few examples of safety-critical embedded systems in aircraft include flight control systems, sensors and actuators, primary flight displays (PFDs), landing gear, pressurization systems and electronic flight instrument systems (EFIS).
Let’s take a look at the flight control system, which in some respects is the most important of all safety-critical systems on a plane. There are primary, secondary, and auxiliary flight control systems. The primary includes the elevator, rudder and aileron controls, while the secondary consists of the elevator and rudder trip tab systems and the auxiliary includes high lift and rear flap systems.
Each of these control surfaces is moved by signals sent from the flight deck controls, and work together to maneuver the plane. On the first airplanes, the flight control systems were mechanical, moved by a series of pulleys, cables, and rods which manipulated the control surfaces to adjust pitch, yaw, and roll. As plane engines became faster, these mechanical systems simply couldn’t deal with the aerodynamic pressure, so hydraulic pumps were incorporated into flight control system designs to help move the control surfaces at high speeds.
Eventually, Flight-By-Wire (FBW) systems were developed, which incorporate fiber optic cables and computers to send signals to the control surfaces electronically. With FBW, the control input from the pilot is analyzed by the flight control computer (FCC) before being transmitted to the control surfaces.
As you can see, there’s a lot going on here. A flaw in any one of the components of an FBW system, for example, can trigger a system-wide error or even failure. Most planes include some redundant backup systems, but no pilot or engineer ever wants it to get to that point, and neither to do we. At Novel, we’ve spent 12+ years designing, building and perfecting safety-critical embedded system solutions (software and electronic) for UAVs and unmanned aircraft systems, helicopters, and airplanes. Bring Novel’s proven safety-critical engineering expertise to your next project. Reach out today and see how we can help.