Aircraft Navigation and Communications

Navigation is the science of determining present location, desired location, obstacles between these locations, and best courses to take to reach these locations. An interesting pioneer of aircraft navigation was James Harold Doolittle (1886-1993).

Best known for his aircraft-carrier-based bomber raid on Tokyo in World War II, General Doolittle received his Master’s and Doctor of Science degrees in aeronautics from Massachusetts Institute of Technology, where he developed instrumental blind flying in 1929. He made navigation history by taking off, flying a set course, and landing without seeing the ground.

For a modern aircraft, with continuous changes in altitude, airspeed, and course, navigation is a challenge. Aircraft computers help meet this challenge by processing the multiple inputs and suggesting aircrew actions to maintain course, avoid collision and weather, conserve fuel, and suggest alternative flight solutions.

An important development in aircraft navigation is the Kalman filter. Welch and Bishop (7) state that in 1960, R.E. Kalman published his famous paper describing a recursive solution to the discrete-data linear filtering problem. Since that time, due in large part to advances in digital computing, the Kalman filter has been the subject of extensive research and application, particularly in the area of autonomous or assisted navigation.

The Kalman filter is a set of mathematical equations that provides an efficient computational (recursive) implementation of the least-squares method. The filter is very powerful in several aspects: It supports estimation of past, present, and even future states, and it can do so even when the precise nature of the modeled system is unknown.

The global positioning system (GPS) is a satellite reference system that uses multiple satellite inputs to determine location. Many modern systems, including aircraft, are equipped with GPS receivers, which allow the system access to the network of GPS satellites and the GPS services. Depending on the quality and privileges of the GPS receiver, the system can have an instantaneous input ofits current location, course, and speed within centimeters of accuracy. GPS receivers, another type ofaircraft computer, can also be programmed to inform aircrews of services related to their flight plan.

Before the GPS receiver, the inertial navigation systems (INS) were the primary navigation system on aircraft. Fink and Christiansen (8) describe inertial navigation as the most widely used ‘‘self-contained’’ technology. In the case of an aircraft, the INS is contained within the aircraft, and is not dependent on outside inputs. Accelerometers constantly sense the vehicle’s movements and convert them, by double integration, into distance traveled. To reduce errors caused by vehicle attitude, the accelerometers are mounted on a gyroscopically controlled stable platform.

Aircraft Communications. Communication technologies on aircraft are predominately radio communication. This technology allows aircrews to communicate with ground controllers and other aircraft. Aircraft computers help establish, secure, and amplify these important communication channels.

These communication technologies are becoming increasingly important as aircraft become interoperable. As the dependency of aircraft on interoperability increases, the requirements to provide better, more reliable, secure point-to-point aircraft communication also increases. The aircraft computer plays a significant role in meeting this challenge by formatting and regulating this increased flow of information.

Aircraft Displays. Displays are visual monitors in aircraft that present desired data to aircrews and passengers. Adam and Gibson (9) illustrate F-15E displays used in the Gulf War. These illustrations show heads-up displays (HUDs), vertical situation displays, radar warning receivers, and low- altitude navigation and targeting system (Lantirn) displays typical of modern fighter aircraft. Sweet (10) illustrates the displays of a Boeing 777, showing the digital bus interface to the flight-deck panels and an optical-fiber data distribution interface that meets industry standards.