Figure 15.24. Auxiliary power unit

15.9.4 Avionics Subsystems

A host of avionics “black boxes” support the flight deck and beyond. The black boxes serve navigation, communication, aircraft-control, and environment-control systems; and record and process important data to analyze and monitor malfunctions and so forth.

With increasing features, the electrical cable length is long and relatively heavy. Multiplexing of data transmission significantly reduces cable weight. Recently, fiber optics have been used for data transmission; when used with a FBW system, it is appropriately termed FBL (see Chapter 12). This section introduces readers to design features (i.e., hardware) that assist in a more accurate prediction of weight and cost.

Most avionics black boxes have microprocessors, which help to standardize connections for data flow. The connection of wires is called a bus. Following are the prevailing standards for a bus architecture.

Military Aircraft Application

MIL-STD-1553B: U.S. military aircraft were the first to use the data-bus architecture, especially to handle the large amount of data for FBW and combat operations. In the United Kingdom, it is covered by DEF STAN 00–18. MIL-STD-1773 is the fiber-optics version of MIL-STD-1553B and STANAG 3838 is the NATO standard for bus architecture.

Figure 15.25. Ram air turbine