Built-in test equipment (BITE)

Built-in test (BIT)

Built-in self test (BIST)

Description

Built-in test equipment (BITE) for avionics primarily refers to passive fault management and diagnosis equipment built into aiborne systems to support maitenance processes. 

Built-in test equipment includes multimeters, oscilloscopes, discharge probes, and frequency generators that are provided as part of the system to enable testing and perform diagnostics.

The acronym BIT is often used for the same function or, more specifically, in reference to the individual tests.

BIT often includes:

• The detection of the fault
• The accommodation of the fault (how the system actively responds to the fault)
• The annunciation or logging of the fault to warn of possible effects and/or aid in troubleshooting the faulty equipment.

Functionality includes:

• Analysis of failure monitoring results
• Reporting and memorisation of failures
• Management of tests
• Having the set adequate parameters for the different compenents

Built-in self test

A built-in self test (BIST) is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as high reliability and lower repair cycle times or constraints such as limited technician accessibility or cost of testing during manufacture.

The main purpose of BIST is to reduce the complexity, and therefore the cost and reduce reliance upon external test equipment.

Almost all avionics incorporate BIST. In avionics the purpose is to isolate failing line-relaceable units (LRUs), which are then removed and repaired elsewhere, usually in depots or at the manufacturer. Commercial aircraft only make money when they fly, so they use BIST to minimise the time on the ground needed for repair and to increase the level of safety of the system which contains BIST. Similar arguments apply to military aircraft. When BIST is used in flight, a fault causes the system to switch to an alternative mode or equipment that still operates. Critical flight equipment is normally duplicated. Less critical flight equipment, such as entertainment systems, might have a "limp mode" that provides some functions.