Are you required to report leaving an altitude if you have been given a crossing restriction? If ATC gives me a clearance to cross a fix at a specific altitude or a descent at pilot's discretion and I read back the clearance, is my readback considered the report specified in the AIM, or do I have to inform them when I actually start down?


  AIM 5-3-3. Additional Reports
  
  a. The following reports should be made to ATC or FSS facilities
  without a specific ATC request:
  
  1. At all times.
  
  (a) When vacating any previously assigned altitude or flight level for
  a newly assigned altitude or flight level.
  
  ...


An Example - Say that a pilot is flying at flight level 340 100 NM from Wilmington VOR and gets the following clearance:


  ATC: N1234, cross Wilmington VOR at flight level 240
  Pilot: Cross Wilmington VOR at flight level 240, N1234


or


  ATC: N1234, descend at pilot's discretion to flight level 240
  Pilot: Descend at pilot's discretion to flight level 240  


It's a little early to start down since we want to stay high for fuel efficiency, so the pilot decides to wait until 30 NM from the VOR to start down.  When they reach that point, are they required to inform ATC before starting the descent or are they considered to have reported the descent earlier?

I hear pilots that do it both ways and each camp is pretty emphatic about it....
I’ve been a controller in both the en route and terminal environments. While I agree with your interpretation of the AIM that it appears to be required, reorting leaving your altitude is not expected and I did not usually hear it done.

To give the perspective from the other side of the mic, an altitude crossing restriction is functionally equivalent to a pilot’s discretion climb/descent to that point. ATC will protect all altitudes between your current one and the restriction, and you are free to hit that restriction as you see fit (barring the violation of other regulations, of course). You may not return to a previously vacated altitude as part of your climb/descent, but you may level.

You are also correct in that it can tie up the freq as an “unnecessary” call, but if you are unsure, better to over inform rather than under inform.

Incidentally, very few controllers read the AIM. The 7110.65 takes precedence, and I’ve actually had a supervisor yell at me for referring to the AIM once. I know, I know.

So, legally, it should be done.  In practice? Unnecessary and I preferred that it not be done when I was working.