SUBSYSTEM INTERDEPENDENCY. A system’s ability to achieve its goal depends on the effective functioning and harmonious interaction of its subsystems. If a vital subsystem fails or becomes defective and can no longer meet its specific objective, the overall system will fail to meet its objective. For exam- ple, if the fuel pump (a vital subsystem of the fuel system) fails, then the fuel system fails. With the fail- ure of the fuel system (a vital subsystem of the automobile), the entire system fails. On the other hand, when a nonvital subsystem fails, the primary objective of the overall system can still be met. For instance, if the radio (a subsystem of the electrical system) fails, the automobile can still convey passengers.
Designers of all types of systems need to recognize the consequences of subsystem failure and provide the appropriate level of control. For example, a systems designer may provide control by designing a