Definition
The frequency at which a component, system, or piece of equipment fails over a given period of operating time, usually expressed as failures per hour or as a probability of failure during a specified interval. In aviation reliability work, it is a statistical measure used to predict how often a part is expected to break down under normal use.
Plain English
How often something is expected to break, expressed as a number rather than a guess. For example, one failure per 10,000 hours of use.
Context Anchor
Seen in instrument flying discussions about equipment reliability, system malfunctions, and backup planning.
Derivation
Failure comes from an older word meaning to be lacking or not succeed. Rate means a measured amount compared with another amount, such as events per hour. Together, failure rate means failures measured against use or time.
Why Pilots Care
Pilots use failure rates to decide on required backups and redundancy for safe IFR operations.
Intuition Check
Failure rate does not mean the part has already failed, and it does not predict the exact flight when it will fail. It means how often failures are expected across many hours, cycles, or uses.
Example Sentence 1
Solid-state attitude indicators have a much lower failure rate than older vacuum-driven gyros, which is one reason modern cockpits have moved away from mechanical instruments.
Example Sentence 2
When planning an IFR flight, the pilot reviewed the failure rates of the attitude and heading systems.