Latent Failure
Section 06: System Safety & Functional Safety
Definition
A failure that is not immediately apparent to the flight crew during normal operations. Latent failures are undetected until revealed by a specific test, inspection, another failure, or a demand on the failed function. In the context of safety assessment, latent failures are significant because they increase exposure time — the period during which the system is operating in a degraded state without the crew's knowledge. The combination of a latent failure and a subsequent active failure can result in a more severe failure condition than either failure alone.
Where This Shows Up
Latent failures are a critical concern in safety analysis. In fault trees, the probability contribution of a latent failure is proportional to its exposure time — the interval between the failure occurring and its detection. Shorter detection intervals (through Built-In Test Equipment, maintenance checks, or periodic testing) reduce the probability contribution of latent failures. Regulatory requirements address latent failures by requiring that no single latent failure in combination with one subsequent active failure can lead to a catastrophic failure condition without some form of indication.
Primary Sources
Addresses latent failure considerations in system safety assessment, including exposure time calculations.
Provides guidance on treatment of latent failures in fault tree analysis and other safety methods.
Related Terms
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