"Teacherjh" wrote in message
...

Well, lets ask the controllers here (rather than AIM, which we all have
access to). On a cruise clearance, for example Cruise 6000, you
observe (mode C) an aircraft has descended from 6000 to 4000.
There is another aircraft which could use the 6000 altitude. You've
received no communications from the aircraft on a cruise (except the
acknowlegement of the clearance). Do you consider the 6000 foot
alititude vacant?


No, the aircraft is entitled to climb back to 6000 if so desired. 6000
becomes available when the aircraft verbally reports leaving 5000.



Same question, but the cruise aircraft has reported descending to 4000.
Has his report of a descent vacated the 6000 foot altitude? (no
bobbing back up)


No, a pilot may not return to an altitude that he's verbally reported
leaving, verbally reporting that he's descending to an intermediate altitude
does nothing.



Same question, but instead of a cruise question, it's a "descend at
pilot's
discretion to 2000". The pilot acknowleges the clearance, and later is
observed at 4000 feet, having not reported the descent.


5000 and 6000 are now available for other aircraft.



Same question, same airplane, but in this case the pilot reported
descending from 6000 to 4000.


No change.