Certified Systems Engineering Professional Csep · Free Practice Question Medium
Question 27
[ID-4006] Choose the right sentence regarding Reliability, Availability & Maintainability (RAM) concepts.
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A
A system can have extremely high reliability and still have low availability.
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B
If a system's downtime increases, its availability increases.
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C
If a system's MTBF increases, its reliability decreases.
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D
A system's operational availability is always higher than its achieved availability.
Reveal correct answer
Correct answer: A
A.
This statement is correct. Reliability refers to the ability of a system to perform its intended function without failure over a specified period of time, while availability refers to the readiness of a system to perform its function when required. A system can have high reliability (low failure rate) but still have low availability if undergoing long preventive maintenance periods due to difficult maintenance tasks (low maintainability) or considerable delay times. See INCOSE SE Handbook 5th Ed. Section 3.1.8, pp. 176-179.
B.
Availability = Uptime/(Uptime + Downtime). Thus, an increase in downtime would promote a decrease in availability. See INCOSE SE Handbook 5th Ed. Section 3.1.8, p.178.
C.
An increase in MTBF actually indicates an improvement in reliability, not a decrease. See INCOSE SE Handbook 5th Ed. Section 3.1.8, pp. 176-178.
D.
Operational availability considers delay times into the equation while achieving availability does not. This means that a system's operational availability will never be higher than its achieved availability. See INCOSE SE Handbook 5th Ed. Section 3.1.8, pp. 178 and 179.
Discussion
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