The intrinsic availability of a system or equipment is the probability that it is operating satisfactorily at any point in time when used under stated conditions, where the time considered is operating time and active repair time.

Thus, intrinsic availability excludes from consideration all free time, storage time, administrative time, and logistic time. As the name indicates, intrinsic availability refers primarily to the built-in capability of the system or equipment to operate satisfactorily under stated conditions.

The effect of these definitions, is essentially to allow realistic assignment of responsibility in case an unsatisfactory situation exists. If an improvement in intrinsic availability is required, responsibility can properly be assigned to the design and production engineers assuming, of course, that the operating conditions are compatible with design specifications. On the other hand, if availability is unsatisfactory and improvement in intrinsic availability is not indicated, the responsibility is properly placed on the management to effect the required improvement by reducing administrative and logistic delay. If neither of these steps is indicated and operational readiness is not satisfactory, improvement depends on changes in free time and storage time, implying more efficient use of the system equipment.

References:

1. MIL-HDBK-338, Electronic Reliability Design Handbook, 15 Oct 84
2. MIL-STD-721, Definitions of Terms for Reliability and Maintainability, 23 Oct 91
3. Bazovsky, Igor, Reliability Theory and Practice
4. O’Connor, Patrick, D. T., Practical Reliability Engineering
5. Birolini, Alessandro, Reliability Engineering: Theory and Practice