What must be attached to an FBR once the 3MC signs it off before sending it off ship?

The requirement for a serial number to be attached to a Functional Build Review (FBR) after it is signed off by the 3MC is important for identification and tracking purposes. The serial number serves as a unique identifier for the specific item or build being reviewed. This is crucial for maintaining accurate records and ensuring that all aspects of the maintenance and material management processes can be traced back to specific components or assemblies. It helps in tracking the lifecycle of the item, ensuring compliance with standards, and facilitating accountability in maintenance activities.

In contrast, while the other options may have their own significance in maintenance processes—such as an approval letter indicating authorization or a completion certificate signifying that a task is finished—these do not serve the same critical role in item identification and tracking as the serial number does. Therefore, attaching the serial number is essential for effective management and oversight of the assets being handled.