RAM Performance Optimization & Availability 2 — Questions and Answers
Question 1: Which metric best quantifies the proportion of time a system is operational and available for use?
- Mean Time Between Failures (MTBF)
- Operational Availability (Ao) (Correct answer)
- Mean Time To Repair (MTTR)
- Failure Rate (λ)
Correct answer: Operational Availability (Ao)
Operational Availability (Ao) is the ratio of uptime to total calendar time, directly expressing what fraction of time a system is available for its intended function.
Question 2: A system has an MTBF of 500 hours and an MTTR of 50 hours. What is its inherent availability?
- 0.90
- 0.91
- 0.95
- 0.909 (Correct answer)
Correct answer: 0.909
Inherent Availability = MTBF / (MTBF + MTTR) = 500 / (500 + 50) = 500/550 ≈ 0.909.
Question 3: What is the primary purpose of 'availability allocation' in system design?
- Assigning availability targets to subsystems so the overall system availability requirement is met (Correct answer)
- Measuring system uptime during field operations
- Scheduling preventive maintenance intervals
- Calculating spare parts inventory levels
Correct answer: Assigning availability targets to subsystems so the overall system availability requirement is met
Availability allocation distributes the top-level availability requirement down to subsystem and component levels to ensure the overall system goal is achievable.
Question 4: In RAM analysis, 'achieved availability' differs from 'inherent availability' primarily because it includes:
- Only unscheduled corrective maintenance downtime
- Both scheduled preventive and unscheduled corrective maintenance downtime (Correct answer)
- Logistics and administrative delays only
- Supply chain lead times for spare parts
Correct answer: Both scheduled preventive and unscheduled corrective maintenance downtime
Achieved Availability (Aa) accounts for both scheduled (preventive) and unscheduled (corrective) maintenance downtime, whereas Inherent Availability excludes preventive maintenance.
Question 5: Which design strategy improves availability by reducing the time required to perform corrective maintenance?
- Derating components
- Increasing redundancy levels
- Improving testability and accessibility (Design for Maintainability) (Correct answer)
- Adding burn-in testing
Correct answer: Improving testability and accessibility (Design for Maintainability)
Design for Maintainability reduces MTTR by improving fault isolation, access, and repair procedures, directly increasing availability.
Question 6: A mission requires 95% availability. If each of three series subsystems must contribute equally, approximately what availability must each subsystem achieve?
- 0.983 (Correct answer)
- 0.950
- 0.967
- 0.999
Correct answer: 0.983
For series systems, overall availability = A^n, so A = 0.95^(1/3) ≈ 0.983 for each subsystem.
Question 7: Which maintenance concept parameter most directly reduces Mean Logistics Downtime (MLDT)?
- Increasing component MTBF
- Improving supply chain responsiveness and pre-positioned spare parts (Correct answer)
- Reducing the number of maintenance technicians
- Extending scheduled maintenance intervals
Correct answer: Improving supply chain responsiveness and pre-positioned spare parts
MLDT is driven by the time waiting for parts, tools, or personnel, so pre-positioned spares and responsive supply chains directly shorten it.
RAM Performance Optimization & Availability 2
Which metric best quantifies the proportion of time a system is operational and available for use?