CMRP Root Cause Analysis and Failure Investigation 2 — Questions and Answers
Question 1: What does FMEA stand for, and what is its primary output?
- Failure Modes and Effects Analysis; a prioritized list of failure risks with recommended actions (Correct answer)
- Functional Maintenance and Equipment Assessment; a maintenance schedule
- Failure Management and Error Analysis; a list of operator errors
- Frequency, Mode, and Effect Assessment; a reliability score
Correct answer: Failure Modes and Effects Analysis; a prioritized list of failure risks with recommended actions
FMEA identifies each potential failure mode, its effects on the system, and its causes, then prioritizes them by Risk Priority Number (RPN) to guide preventive action.
Question 2: In FMEA, what does the Risk Priority Number (RPN) represent?
- The product of severity, occurrence, and detection scores used to rank failure mode risk (Correct answer)
- The number of times a failure mode has occurred historically
- The cost of repairing a failure mode when it occurs
- The number of personnel required to address a failure
Correct answer: The product of severity, occurrence, and detection scores used to rank failure mode risk
RPN = Severity × Occurrence × Detection, where each factor is rated on a scale (typically 1–10), giving a composite risk score to prioritize corrective actions.
Question 3: What is a 'failure mode' in the context of reliability engineering?
- The specific way in which a component or system fails to perform its required function (Correct answer)
- The frequency at which a component fails over time
- The cost associated with a particular type of failure
- The corrective action taken after a failure occurs
Correct answer: The specific way in which a component or system fails to perform its required function
A failure mode describes the observable manner in which a failure occurs (e.g., fracture, wear, corrosion, leakage), distinct from the cause or effect of that failure.
Question 4: Which type of failure pattern shows a high initial failure rate, low mid-life rate, and increasing rate at end of life—commonly called the 'bathtub curve'?
- Pattern A (bathtub) (Correct answer)
- Pattern B (wear-out)
- Pattern C (fatigue)
- Pattern F (random)
Correct answer: Pattern A (bathtub)
Pattern A (the bathtub curve) has three zones: infant mortality (early failures from defects), random failures (stable mid-life), and wear-out (age-related degradation).
Question 5: In a root cause analysis investigation, why is it critical to preserve the failure scene before disassembly?
- Physical evidence of failure origin, direction of propagation, and contributing conditions may be destroyed during disassembly (Correct answer)
- Regulatory agencies require photographic evidence before any repairs
- Insurance claims cannot be filed without a preserved failure scene
- Preservation prevents contamination of parts going to the laboratory
Correct answer: Physical evidence of failure origin, direction of propagation, and contributing conditions may be destroyed during disassembly
Premature disassembly can destroy fracture surfaces, wear patterns, and positional evidence that are essential to correctly identifying the failure mechanism and root cause.
Question 6: What is the difference between a 'chronic failure' and a 'sporadic failure' in reliability analysis?
- Chronic failures recur frequently at low impact; sporadic failures are sudden, high-impact deviations from normal performance (Correct answer)
- Chronic failures are electrical; sporadic failures are mechanical
- Chronic failures occur in old equipment; sporadic failures occur in new equipment
- Chronic failures have known causes; sporadic failures have unknown causes
Correct answer: Chronic failures recur frequently at low impact; sporadic failures are sudden, high-impact deviations from normal performance
Chronic failures are recurring, low-visibility losses (e.g., frequent small leaks) often accepted as normal, while sporadic failures are sudden, obvious deviations that trigger immediate response.
CMRP Root Cause Analysis and Failure Investigation 2
What does FMEA stand for, and what is its primary output?