III. Read and translate the text. Put the words dealing with avionics architecture in the correct place in the text

Before the 1960s, electrical and electronic systems on aircraft consisted of independent subsystems, each with its own sensors, analog computers, displays, and controls. The appearance of airborne digital computers in the 1960s created the first integrated avionic systems. The interconnectivity of airborne electronics is called architecture. It involves some aspects:

1. ________________ They present information from the avionics to the pilots. The information consists of vertical and horizontal navi­gation data, flight-control data (e.g., speed and angle of attack), and com­munication data (radio frequencies). The displays show the status of all subsystems including their faults. Displays consist of dedicated gauges, dedicated glass displays, multipurpose glass displays, and the support­ing symbol generators. In 1996, flat-panel vertical- and horizontal-situa­tion displays were displacing cathode-ray tubes as “glass displays”. Mul­tipurpose displays of text and block diagrams are flat-panel matrices sur­rounded by buttons whose labels change as the displays change. On-board digital terrain data, used for mission planning, can be displayed on the horizontal situation display or on a head-up display.

2. ________________ The means of inputting information from the pilots to the avionics. The flight controls traditionally consist of rudder pedals and a control-column or stick. Fly-by-wire aircraft are increasingly using either two-axis hand controllers and rudder pedals or (especially in manned spacecraft) three-axis hand controllers. The subsystem controls consist of panel-mounted buttons and switches. Switches are also mounted on the control column, stick, throttle, and hand-controllers; sometimes 5 buttons per hand. The buttons on the periphery of multipurpose displays control the subsystems.

3. _________________ The method of processing sensor data. Two extreme organizations of computation exist:

Centralized. Data from all sensors are collected in a bank of central computers in which software from several subsystems are intermingled. The level of fault tolerance is that of the most critical subsystem, usually flight control. It has the simplest hardware and interconnections. In 1996, central computers were redundant uniprocessors or multipro­cessors.

Decentralized. Each traditional subsystem retains its integrity. Hence, navigation sensors feed a navigation computer, flight-control sensors feed a flight-control computer that drives flight-control actuators, and so on. This architecture requires complex interconnections but has the advantages that fault-tolerance provisions can differ for each subsystem according to the consequences of failure and that software is created by experts in each subsystem, executes independently of other soft­ware, and is easily modified. When designed with suitable inter-com­puter channels and data-reasonability tests, decentralized systems have more reliable software than do centralized systems.

Many avionic systems combine features of centralized and decentralized architectures.

4. _______________________ Copper or fiber-optic paths among sensors, computers, actuators, displays, and controls. Some data paths are dedicated and some are multiplexed. Complex aircraft contain parallel buses (one wire, pair of wires, or optical fiber per bit) and serial buses (bits sent sequentially on one wire-pair or fiber). A large aircraft can have a thousand pounds of signal wiring.

5. ________________________ Commercial fly-by-wire aircraft sometimes divide the avionics into a highly redundant safety-critical flight-control system, a dually redundant mission-critical flight-management system, and a nonredundant maintenance system that collects and records data. Military air­craft sometimes partition their avionics for reasons other than safety.

6. _________________________ Avionic equipment are subject to aircraft-generated electric-power transients, whose effects are reduced by filtering and batteries. Equipment are also subject to externally generated disturbances from radio transmitters and lightning. The effects of external disturbances (high-intensity radiated fields, HIRF) are reduced by shielding metal wires and by using fiber optic data buses. Aircraft constructed with a con­tinuous metal skin have an added layer of Faraday shielding. Neverthe­less, direct lightning strikes on antennas destroy input circuits and may damage feed cables. A nearby strike may induce enough current to do the same. Composite airframe structures can be transparent to radiation, thus exposing the avionics and power systems to external fields.

Standards. The signals in space created by navaids are standardized by the International Civil Aviation Organization (ICAO), Montreal, a United Nations agency. These standards are written by committees that con­sist of representatives of the member governments. Interfaces among airborne subsystems, within the aircraft, are standardized by ARINC (Aeronautical Radio, Inc.), Annapolis, Maryland, a nonprofit organiza­tion owned by member airlines. Other requirements are imposed on airborne equipment by two nonprofit organizations supported by member entities (mostly airframe and avionics manufacturers and gov­ernment agencies). In the United States, RTCA, Inc. (Formerly Radio Technical Commission for Aeronautics), Washington D.C., defines the environmental specifications for airborne hardware and software, and writes performance specifications for airborne equip­ment. In Europe, EUROCAE (European Organization for Civil Avi­ation Equipment), Paris, produces specifications for airborne equipment, some of which are in conjunction with RTCA. Government agen­cies in all major nations define rules governing the usage of naviga­tion equipment in flight, weather minimums, traffic separation, ground equipment required, pilot training requirements, and so on. Some of these rules are standardized internationally by ICAO. U.S. military organizations once issued their own standards for airborne circuit boards but have accepted civil standards since the early 1990s.