At the start of project execution a key resource will be unavailable for two weeks, potentially causing a schedule delay. What should the project manager do first?

The project manager should first update the resource management plan and resource allocation chart because this issue directly impacts resource availability and allocation. These documents guide how resources are acquired, managed, and released, and updating them ensures the project's resource strategy reflects the new reality. This foundational step allows for a structured approach to addressing the unavailability. Reassigning tasks and requiring double shifts (an immediate solution) or updating the schedule (a consequence) are actions that might follow, but the initial step is to formally document the change in resource planning. Requesting a replacement from HR is a potential solution, but the resource management plan should be updated first to reflect the need and strategy for obtaining that replacement. The risk register might be updated if this was an unforeseen event, but the immediate impact is on resource allocation.