What is the correct phraseology for assigning a block altitude?

The phraseology "Maintain block one-five thousand through one-seven thousand" is correct for assigning a block altitude. This terminology clearly and concisely informs the pilot that they are to maintain their altitude within a specified range, which in this case is from 15,000 feet to 17,000 feet. The use of the term "block" indicates that the aircraft should operate anywhere within that altitude range at the discretion of the pilot, as long as they remain within the specified limits.

The precision in this phrasing is essential for effective communication between air traffic control and pilots, ensuring safety and clarity in altitude management. It clearly defines both the lower and upper limits of the altitude block, which helps prevent misunderstandings about altitude assignments.