RAM Advanced Techniques & Methods 3 — Questions and Answers
Question 1: Which Markov model state transition correctly represents a two-component active parallel system with identical failure rate λ and repair rate μ?
- States: both-up → one-up → failed; transitions depend on 2λ and λ from each state
- States: both-up → one-up → failed; transitions are λ from both states and μ from failed only
- States: both-up → one-up → failed; transitions are 2λ, λ, and μ at each repair state (Correct answer)
- States: both-up → failed; no intermediate state needed
Correct answer: States: both-up → one-up → failed; transitions are 2λ, λ, and μ at each repair state
With two active components, the system transitions from both-up at rate 2λ, from one-up at rate λ, with repair transitions at rate μ from each failed/degraded state.
Question 2: What is the primary purpose of a Reliability Growth test program using the AMSAA/Crow model?
- Qualify components to a specified MTBF before production
- Track and demonstrate improvement in reliability over successive test-fix-test cycles (Correct answer)
- Determine failure modes under accelerated stress conditions
- Validate redundancy effectiveness in operational environments
Correct answer: Track and demonstrate improvement in reliability over successive test-fix-test cycles
The AMSAA/Crow model tracks cumulative failures vs. cumulative test time to quantify reliability growth achieved through iterative test-find-fix cycles.
Question 3: In maintainability demonstration testing, which statistical distribution is typically used to model active corrective maintenance time?
- Normal distribution
- Exponential distribution
- Lognormal distribution (Correct answer)
- Weibull distribution
Correct answer: Lognormal distribution
Active corrective maintenance time is typically modeled with a lognormal distribution because repair times tend to be positively skewed with a lower bound at zero.
Question 4: What does 'operational availability' (Ao) account for that 'inherent availability' (Ai) does not?
- Only corrective maintenance downtime
- Preventive maintenance and logistic/administrative delays (Correct answer)
- Component failure rates alone
- Only scheduled maintenance downtime
Correct answer: Preventive maintenance and logistic/administrative delays
Operational availability includes all downtime sources — corrective, preventive maintenance, and logistic/administrative delays — while inherent availability only considers active repair time.
Question 5: Which design technique intentionally introduces a weak link to protect more critical system components from catastrophic damage?
- Derating
- Fuse/sacrificial element design (Correct answer)
- Redundancy
- Sneak circuit analysis
Correct answer: Fuse/sacrificial element design
Sacrificial elements (like electrical fuses or mechanical shear pins) are designed to fail first, protecting more valuable or safety-critical downstream components.
Question 6: In the Physics of Failure (PoF) approach, what is the primary input used to predict component life?
- Historical field failure databases
- Stress-strength models based on material properties and loading (Correct answer)
- Generic MIL-HDBK-217 failure rate tables
- FMEA severity rankings
Correct answer: Stress-strength models based on material properties and loading
PoF uses fundamental stress-strength models grounded in material science and mechanics to predict failure onset based on actual load and material properties.
Question 7: When performing a sensitivity analysis on a fault tree, which importance measure quantifies how much the system failure probability would decrease if a basic event were made perfectly reliable?
- Birnbaum importance measure
- Criticality importance measure
- Fussel-Vesely importance measure
- Risk reduction worth (RRW) (Correct answer)
Correct answer: Risk reduction worth (RRW)
Risk Reduction Worth (RRW) measures the ratio of current system failure probability to the probability if the component were made perfectly reliable, quantifying maximum achievable improvement.
RAM Advanced Techniques & Methods 3
Which Markov model state transition correctly represents a two-component active parallel system with identical failure rate λ and repair rate μ?