How must the CAA ID be worn by personnel?

The correct answer emphasizes that the CAA ID must be visible at all times to ensure that personnel are easily identifiable within the airside environment. This visibility is crucial for several reasons, including maintaining security protocols, facilitating efficient monitoring by airport authorities, and ensuring that personnel can be recognized as authorized access holders. By having the CAA ID clearly displayed, it helps in quick identification during any security checks and supports a safer airport operation by allowing staff to be recognized by their peers and security personnel alike.

The other choices do not fulfill the requirement for visibility. While wearing the ID in a wallet, on a lanyard, or on the wrist may still display the ID to some extent, these methods may not guarantee that the ID is always visible. Therefore, the emphasis lies on ensuring that the ID is accessible and easily readable at all times while personnel are in airside areas.