BIST reduces cost in two ways: Both lead to a reduction in hourly charges for automated test equipment (ATE) service.
In avionics, the purpose is to isolate failing line-replaceable units, which are then removed and repaired elsewhere, usually in depots or at the manufacturer.
When BIST is used in flight, a fault causes the system to switch to an alternative mode or equipment that still operates.
Less critical flight equipment, such as entertainment systems, might have a "limp mode" that provides some functions.
Built-In-Self-Test is used to make faster, less-expensive integrated circuit manufacturing tests.
The typical personal computer tests itself at start-up because it's a very complex piece of machinery.
This contains complex electronics to accumulate telephone lines or data and route it to a central switch.
Telephone concentrators test for communications continuously, by verifying the presence of periodic data patterns called frames (See SONET).
Safety-critical devices normally define a "safety interval", a period of time too short for injury to occur.
The Minuteman was one of the first major weapons systems to field a permanently installed computer-controlled self-test.