Glossary · Fault behavior and system states
Degraded mode
Also known as: degraded operation
In functional safety and systems engineering, degraded mode is a controlled operating condition with reduced capability following a fault or the loss of a dependency. The reduction is planned and its limits are defined.
- Functional safety
- Integrated systems
In one sentence
Degraded mode keeps a system running with reduced capability after a fault; it must be planned, limited in time and scope, and visible to operators.
Example
After losing its connection to the fleet manager, an AGV finishes its current transport at reduced speed using its onboard map and then stops at the next waiting point.
How it applies
- Functional safety: Degraded mode is an operating condition like any other and must be covered by the risk assessment. Define which safety functions remain available, the permitted limits (speed, force, zones) and how long the system may stay degraded before it has to stop.
- Integrated systems: Connected systems must know that a partner is degraded, for example through a state signal, and adapt; otherwise they keep sending work it cannot handle.
- Technical documentation: The operating manual should describe how degraded mode is indicated, what operators may and may not do, and how normal operation is restored (recovery behavior).
Degraded mode vs. fail-operational behavior
Fail-operational behavior is the design property of continuing to operate despite specified faults; degraded mode is one condition in which that operation can take place. A fallback is the alternative behavior that often leads into it.