Termination of the ability of an item to perform its specified function. OR, Non-conformance to some defined performance criteria. Failures may be classified by:

Meaningless without performance spec

1. Cause

   Misuse: Caused by operation outside specified stress.

   Primary: Not caused by an earlier failure.

   Secondary: Caused by an earlier failure.

   Wearout: Caused by accelerating failure rate mechanism.

   Design: Caused by an intrinsic weakness.

Chapter 2

Software: Caused by a program error despite no hardware failure

Chapter 17

1. Type

   Sudden: Not anticipated and no prior degradation.

   Degradation: Parametric drift or gradual reduction in performance.

   Intermittent: Alternating between the failed and operating condition.

   Dormant: A component or unit failure which does not cause system failure but which either hastens it or, in combination with another dormant fault, would cause system failure.

   Random: Failure is equally probable in each successive equal time interval.

   Catastrophic: Sudden and complete.

The outward appearance of a specific failure effect (e.g. open circuit, leak to atmosphere).

Chapter 2

The physical or chemical process which causes the failure.

Chapter 11

The number of failures of an item per unit time.

Per hour, cycle, operation, etc.

1. Observed failure rate: as computed from a sample.

2. Assessed failure rate: as inferred from sample information.

3. Extrapolated failure rate: projected to other stress levels.

Point estimate Involves a confidence level