failoperate

Failoperate, sometimes written fail-operate or fail-operational, is a design objective in safety-critical systems whereby the system remains functional following the failure of a component or subsystem. The goal is to preserve essential operations and availability, potentially in a degraded mode, until faults are repaired or full restoration occurs.

It is distinguished from fail-safe design, which aims to drive the system to a safe state after a fault. Failoperate emphasizes continuity of operation rather than immediate shutdown.

Key approaches include redundancy (such as N+1 or 1+1 architectures), failover mechanisms that automatically switch to spare components, diversity to reduce common-mode failures, and robust health monitoring and fault isolation. Degraded modes, cache, power backup, and hot-swappable modules also contribute to fail-operational behavior. System designers often perform fault trees and reliability analyses to ensure required availability targets.

Industries that adopt failoperate concepts include aviation and aerospace for flight control, rail and public transit signaling, electrical power systems, data centers, medical devices, and industrial automation. In automotive, advanced driver-assistance and autonomous systems increasingly rely on fail-operational architectures to handle sensor or processor failures.

Terminology varies; some sources use fail-operational, fail-operate, or failover to describe related but distinct concepts. Standards such as IEC 61508, ISO 26262, and EN 50126 address functional safety and fault tolerance, guiding the design of systems intended to remain operational through faults, though the exact usage of the term failoperate may differ by field.

Despite its benefits, failoperate designs can be more complex, expensive, and risk-prone if not properly implemented, and are typically judged against required availability and safety requirements.