In military high performance aircraft the concept of operation might be considerably different, e.g. the control of the autopilot modes and settings integrated in a HOTAS (Hands on Throttle and Stick) concept. Before the advent of FBW technology autopilots were in use temporarily displacing the pilot in operating on the primary flight control organs by meshing into the mechanical linkages, causing the control stick to move according to the nested outer and inner loop commands of the autopilot. Today, autopilots may be integrated into aircraft equipped with an AFCS in FBW technology. In this case the autopilot will only generate so called outer-loop-guidance-commands (OLG) which will be processed by the AFCS inner control loops. Finally, on the fourth level the interaction of the pilot with the automated system is again changed in a radical manner. On this level so called Flight Management Systems (FMS) integrate various navigation, guidance and management functions. Traditionally, flight navigation was supported by various automated sub-systems covering very specific functionalities used to determine the position of the own aircraft. Mainly these were inertial navigation and radio navigation. More recently satellite navigation technologies came along. While in former days until the 1970ies it was the duty of a dedicated person in the cockpit, i.e. the navigation officer, to integrate the information provided by the various navigation aids, the early Navigation Management Systems integrated these functions into one single system entity, functioning mostly automatic. Since then, especially with the advent of digital computer technology in avionics systems Flight Management Systems evolved rapidly. Main functional characteristics of modern FMS can be classified into three main categories:
1. Position determination - integration of navigation information aiming at providing a navigational solution of high precision and integrity
2. Route planning - storage of the flight plan and optionally a secondary flight plan - support for manipulating the flight plan, i.e. navigational databases, automated planning functions - calculation of trajectory predictions, e.g. for precise flight timing - providing access to database information, e.g. routes, waypoints, navaids, airfields - performance and resources calculations, e.g. optimal speed, distances, arrival times, fuel, top-of-decent
3. Guidance computation - generation of outer-loop-guidance-commands for automatic flight plan following, - monitoring of the flight progress - management and provision of information for display on the Control and Display Unit (CDU) and the Electronic Flight Instrumentation System (EFIS) The various sub-systems can be accessed via moding keys.
Data shall be entered via an alphanumerical keypad. Line select keys allow the direct ineraction with software menus displayed on the screen. Suchlike single-box solutions, sometimes even the flight management computer was hosted by the CDU, were strongly motivated by the fact that when FMS first entered flight-decks, they were usually introduced as retrofit and therefore had a rather low degree of integration with other systems. In most recent flight-deck designs, e.g. the A380, the FMS is controlled in a more GUI-style (Graphical User Interface) interaction, using multifunctional head-down displays, trackball and standard QWERTY keyboard. This approach allows e.g. an easy geometrical manipulation of flight plan information on a map display. Another feature of modern FMS is the integration into information networks such as e.g. ADS-B (Automatic Dependent Surveillance-Broadcast), TIS-B (Traffic information services-broadcast) or CPDLC (Controller Pilot Data Link Communications) to the main purpose of air traffic management and deconfliction. The variety of information provided by the diverse means of control automation including the communication systems described above will be displayed on an Electronic Flight Instrument System (EFIS) replacing the traditional electromechanical cockpit instruments and gauges of former times in modern flight-decks. An EFIS usually consists of several Multi Function Displays (MFDs). These glass cockpit displays being capable of displaying and interacting with various display formats, the most common of which are the Primary Flight Display (PFD) and the Navigation Display (ND). Furthermore, many additional display formats are in use conveying information about various aircraft systems, such as propulsion, fuel or electrical systems. Systems like ECAM (Electronic Centralised Aircraft Monitor) or EICAS (Engine Indicating and Crew Alerting System) go beyond the pure display of status information by also providing corrective action to be taken by the flight crew in case of system failures, as well as system limitations resulting from these failures. While ECAM or EICAS only consider the internal status of the basic aircraft systems and the engine, providing advice and warning to the flight-deck crew, there further exist dedicated warning systems concerning the external situation of the aircraft such as traffic and ground proximity. The Traffic Alert and Collision Avoidance System (TCAS) is designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft independent of air traffic control. It warns the flight-deck crew of the presence of other aircraft which may present a threat of mid-air collision. TCAS is a cooperative system in a sense that only transponderequipped aircraft can in principle participate.
TCAS is an implementation of the Airborne Collision Avoidance System (ACAS) standard mandated by the International Civil Aviation Organization (ICAO). Depending on the implementation version TCAS provides traffic information (TA, Traffic Advisory) and direct instructions to minimise the danger of collision (RA, Resolution Advisory) by vertical manoeuvres. Future implementations will include advices for lateral evasive manoeuvering. In order to counteract the occurrence of CFIT (Controlled Flight into Terrain) accidents, so-called Terrain Awareness and Warning Systems (TAWS) are in use in civil aircraft. The first-generation of these TAWS systems is known as Ground Proximity Warning System (GPWS), which uses the radar altimeter information to determine terrain closure. This system has now been further improved by use of digital terrain elevation databases. The TAWS calculates interferences of the anticipated flight trajectory with the digital terrain by use of integrated navigation information. In case of hazardous approach to terrain, warnings will be issued to the flight-deck crew. The availablility of digital terrain elevation data allows the display of terrain information and proximity on the navigation display or even as threedimensional perspective view. In summary, aircraft guidance and control systems are probably the most comprehensive ones at the time being compared to corresponding systems in other categories of vehicles.
They evolved in the meantime from a design tradition of more than hundred years and cover about all tasks which might occur during flight. Up to now, though, there are very few exemptions in operational aircraft to the traditional design principle of exclusively letting the pilot decide which task has to be carried out at whatever flight situation. One exemption is the terrain avoidance mode in some fighter aircraft, where an automatic pull-up manoeuvre takes place in case of being too close to the terrain at high speed. With the ongoing advent of unmanned aerial vehicles this will change.. In turn, the experience with unmanned aircraft surely will eventually have an impact on the design of guidance and control systems for future manned aircraft, too.
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1. Automatic systems for guidance and control in automotive vehicles
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