Availability

Availability is a system feature closely connected to the reliability of the components and their maintainability. There are different types of availability; the more used are: the Inherent availability, the Achieved Availability and the Operational Availability.

Inherent Availability

The Inherent Availability is the probability that the system is operating or ready to operate, by considering only the failures as causes of unavailability. It is connected to the Reliability, Maintainability and Testability of the system.

Achieved Availability

The Achieved Availability is the probability that the device is operating or ready to operate, by including also the aspects related to preventive maintenance. It is connected to the Reliability, Maintainability, Testability and the Reliability Centered Maintenance of the system.

Operational Availability

Operational Availability is the probability the System is operational or ready to operate, by including also the effectiveness and efficiency of the logistics support. It takes into account the additional downtimes due to administrative delays, possible awaiting of spare parts, personnel or equiments needed to perform maintenance and that are not immediately available.