What is the required phrase for responding to a request for a block altitude?

The correct response to a request for a block altitude is structured to efficiently communicate the status of the request. When choosing the response "ACID, request, approved," it clearly indicates that the request has been considered and accepted. This phraseology is straightforward and complies with standard communication protocols, ensuring clarity and efficiency in operations.

Using this format reinforces operational safety and efficiency, as it specifies the Aircraft Call Sign (ACID) and explicitly conveys approval, thus providing the pilot or operator with the necessary information to proceed with their flight plan under the approved altitude block.

Other options, while they may have their own contexts, either do not confirm the approval status, which is critical in this scenario, or imply an indecision or a negative response that does not align with what is being requested. Therefore, the clarity of communication in the correct response is paramount in aviation practices, ensuring all parties have a mutual understanding of the altitude clearance.