Keith Smith wrote:My guess is the origin of this requirement comes from non-radar separation being used in holding stacks. When you have a bunch o' planes holding at a fix with 1k vertical separation. As the aircraft in the bottom of the stack leaves the hold, each plane above can be given a new (previously occupied) altitude to descend to as soon as the aircraft below reports leaving said altitude. In those cases, there's a tangible use for the 'leaving [altitude]' call from the pilots.
I’m not so certain that’s relevant to this situation. The posts above are in regards to a pilot discretion descent. I can’t think of an instance where a busy controller with a thick holding stack would issue a PD descent when they really need to use that leaving altitude. If the controller really needs to assign the altitude that the aircraft is leaving, there will be nothing PD about it.
Further, a PD descent requires a report 1000ft below the altitude before it becomes assignable since an aircraft who reports leaving 15,000 in a PD descent could level at 14,900 if they wanted to. A non-PD descent can free up the reported leaving altitude pending both aircraft are of like type.