Final answer:
To ensure the carabiners are locked, the Controller must visually verify them on the ripcord puller's side of the boarding platform.
Step-by-step explanation:
The subject of this question is Safety. The question is asking about the procedure to ensure the carabiners are locked before replying 'Carabiners Locked.' The Controller needs to move to the ripcord puller's side of the rolling boarding platform and visually verify the carabiners are locked. This step is crucial to ensure the safety of the operation.