In engineering, redundancy is the duplication of critical components or functions of
a system with the intention of increasing reliability of the system, usually in the
form of a backup or fail-safe, or to improve actual system performance, such as in
the case of GNSS receivers, or multi-threaded computer processing.
In many safety-critical systems, such as fly-by-wire and hydraulic systems in
aircraft, some parts of the control system may be triplicated, which is formally
termed triple modular redundancy.
An error in one component may then be out-voted by the other two. In a triply
redundant system, the system has three sub components, all three of which must
fail before the system fails. Since each one rarely fails, and the sub components
are expected to fail independently, the probability of all three failing is calculated to
be extraordinarily small; often outweighed by other risk factors, such as human
error. Redundancy may also be known by the terms "majority voting systems" or
"voting logic". Redundancy sometimes produces less, instead of greater reliability –
it creates a more complex system which is prone to various issues, it may lead to
human neglect of duty, and may lead to higher production demands which by
overstressing the system may make it less safe.