N74Y has been cleared to descend from 8,000 feet at pilot's discretion. When can N4567B be assigned 8,000 feet?

The situation involves managing vertical separation between two aircraft, N74Y and N4567B. N74Y has been given the authority to descend from 8,000 feet at the pilot's discretion, meaning that the pilot will choose when to start and when to stop their descent.

Assigning 8,000 feet to N4567B is permissible when N74Y is no longer in a position that could compromise the separation standards. Specifically, waiting for N74Y to report leaving 7,000 feet ensures that there will be adequate vertical separation maintained. This is essential since, at 8,000 feet, N4567B cannot be directed to that altitude until N74Y has already descended to below that level.

At the point when N74Y reports leaving 7,000 feet, N4567B can safely be assigned 8,000 feet because there's confirmation that the descent has commenced and separation between the two aircraft is ensured. The other choices would not provide the same level of assurance in maintaining safe vertical separation, either allowing too little distance or not accounting for the aircraft's state in relation to the assigned altitude.