Capt.Doug writes:

The profile in the FMS is for efficiency and does not take other traffic
into account. You must wait until ATC explicitely clears you to another
altitude.

So it would probably be best to set the MCP to prevent any descent
until I'm cleared, then?

If you are about to pass the FMS's descent point, politely prompt
ATC for a lower altitude.

"Request descent," or something, I presume.

Going into LAS, you very well may get vectors off
the planned route so that ATC can adequately space the arrival traffic (in
the real world).

In simulation, too, even though traffic is sometimes too light to
justify it (the ATCs need practice as well). In fact, it seems that I
almost never follow the arrival procedure as published. Often just as
I'm beginning it, ATC gives me other instructions. I suppose it's a
bit of a relief as then all I have to do is follow their instructions,
rather than try to follow the arrival chart (but if the FMC is doing
it, it's easy).

No. That would be for lateral navigation only unless explicitely cleared for
different altitudes.

Is there a specific phrasing that means "you can do your own lateral
AND vertical navigation"? Or does ATC as a rule never let IFR flights
select their own altitudes?

Here is an example that one of my colleagues recently
received counseling about. He was cleared via the KORRY 3 arrival into KLGA.
He started to descend according to the profile. ATC asked why he was
descending and to call a number after landing (not good). He was cleared via
the KORRY 3, not cleared to descend via the KORRY 3. Slight difference, but
very important for traffic seperation.

Hmm. I just assumed that since the plates usually indicate altitudes,
"cleared via the KORRY 3" would necessarily mean following both the
course and altitude indications. What does ATC say if they want you
to follow everything on the plate, including the indicated altitudes?

Did your colleague get into significant trouble?

Yes, the Aeronautical Information Manual states that a pilot should advise
when leaving an altitude.

OK.

Yes.

OK, so should I say something like "leaving FL290 for 12000 at CLARR,"
assuming I'm already cleared to descend at my discretion?

Query ATC for the assigned altitude so that both of you are on the same
page. Climbs are the same as descents. 'resume own navigation' is for
lateral flight. Don't climb unless expicitely assigned a new altitude by
ATC.

So there is no equivalent of "resume own navigation" for altitude,
like "resume own altitude," or whatever?

If ATC regularly overrides the plates and (apparently) doesn't often
clear anyone to follow the altitude indications on the plates, why do
all the approach plates seem to mention altitudes? Just for radio
loss? (Except they often seem to have separate procedures for
communications loss.)

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