When conducting a search for missing tools, which step follows a thorough search if the tool is still not found?

When a thorough search for a missing tool has been completed and the tool is still not found, the appropriate next step is to notify the Maintenance Officer. This action is vital because the Maintenance Officer holds a position of authority and responsibility and can initiate further action to mitigate any potential safety issues or operational disruptions stemming from the missing tool.

Notifying the Maintenance Officer ensures that there is a record of the incident, which is crucial for maintaining accountability and safety within the maintenance environment. This also allows the officer to assess the situation and determine if additional resources or searches are necessary.

In addition, the other options may not be the most effective immediate next steps. Placing the aircraft in "down" status would typically be a response after all necessary protocols, including notifying the Maintenance Officer, have been considered. Conducting a second search may not be the best follow-up step without taking action to report the missing tool first, as it does not resolve the issue of accountability and could lead to redundant efforts. Changing the tool inventory may be necessary later but is not an immediate response to the situation at hand, which is focused on understanding the missing tool's status and implications for safety and operations.