In general, service providers have only placed system availability requirements on equipment providers for unplanned system downtime. However, reliability expectations of service providers are shifting in a manner that places requirements on equipment providers to manage all system downtime (i.e., planned system downtime as well as unplanned system downtime) rather than focusing solely on guaranteeing unplanned system downtime. Furthermore, service providers continuously request improvements in total system availability (e.g., requiring 99.999% system availability, which translates to 5.25 minutes of total system downtime per year). While numerous models exist for modeling unplanned system downtime, there are no equivalent models for planned downtime. This paper presents a planned downtime event taxonomy, characterizes the planned downtime for each category in the taxonomy, and incorporates the results into a model for predicting the total planned downtime associated with a system. It then uses the model on an example system, demonstrating the capability of the model in assessing various system design alternatives.