Confusion about when it's my navigation, and when it's ATC

Pixel Dent writes:

That doesn't mean you can't ask for a descent when your FMS tells you it
wants to start down, but there are a number of reasons you may not get
it. There may be conflicting traffic below you or the controlling
authority for the area you are in may have letters of agreement with the
surrounding areas that specify what altitude flights heading in various
directions or to various destinations must be at. In addition sometimes
the controller you're talking to doesn't control the altitude you want
to head down to. For a given ground position there may be three
different controllers handling different altitude blocks and your guy
may not have time to coordinate or even be allowed to descend flights
into the area below you.

OK. But this is a bit worrisome in that the FMC apparently already
calculates the optimal descent. If I can't start down in time, I may
not be able to make the other altitudes in the route without holding
or some other diversion to provide more time to descend. For some
reason, the FMC seems to be optimistic about how quickly it can force
the aircraft down. I have to deploy spoilers a lot, and that's even
when the descent starts on time.

Anyway, so I can just say "request descent" when I'm ready to start
down?

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In article ,
Mxsmanic wrote:

OK. But this is a bit worrisome in that the FMC apparently already
calculates the optimal descent. If I can't start down in time, I may
not be able to make the other altitudes in the route without holding
or some other diversion to provide more time to descend. For some
reason, the FMC seems to be optimistic about how quickly it can force
the aircraft down. I have to deploy spoilers a lot, and that's even
when the descent starts on time.


Well, I don't fly airliners. I fly a single engine prop that rarely sees
anything above 9000'. That being said I fly a lot of IFR and have never
heard a pilot say "Center, my FMC says I need to start descending now."
Somehow in real life they manage it.

If you're having trouble descending fast enough in the Sim maybe you
just need to slow down the plane to give you more time.

Anyway, so I can just say "request descent" when I'm ready to start
down?

Sure. But even if it's approved that doesn't mean you can just descend
at will to the airport. What you're likely to get is something like
"AB123, descending and maintain one two thousand expect lower in 20
miles."

In general what happens is you gradually get "stepped down" in altitude
via a series of descents as you get closer to the airport until the
final approach controller gets you down to whatever altitude is needed
to start your approach (usually something like 2000' AGL). Once you're
given each new altitude assignment the controller really wants you to
hurry down to the next altitude and level off there so you get out of
the way of other traffic. At times you'll even get requests like "AB123
I need best speed down to one five thousand, I have conflicting
traffic."

To really get a feel of how this all works I'd suggest you go to one of
those live atc sites and listen to an approach controller. You'd be
amazed how much you can learn listening to one for a half hour. At first
it will seem chaotic and then you'll realize there are patterns to what
he's doing with the planes.

"Mxsmanic" wrote in message
...

Anyway, so I can just say "request descent" when I'm ready to start
down?

Affirm, exactly that. And if you are not going to collide against another
aircraft or terrain, they usually clear you to descend.

Gus Cabre
EGYC

On 2007-01-03, Mxsmanic wrote:
Pixel Dent writes:

I think I read this section before; this paragraph sounds familiar. I
always get instructions to "maintain," though. What's the phraseology
when I get a block of altitudes? Or does it even happen with
frequency in real life? How do I request it (or do I even need to
request it)?

From a flight today, west of Billings, MT:

N12345: Unable to maintain 16,000 for turbulence.
ATC: N12345 maintain between 14,000 and 16,000

or you can just request it directly:

N12345: Request block altitude between 15,000 and 17,000.
ATC: N12345 maintain block altitude between 15,000 and 17,000.

-Milen

Milen Lazarov writes:

or you can just request it directly:

N12345: Request block altitude between 15,000 and 17,000.
ATC: N12345 maintain block altitude between 15,000 and 17,000.

I'll try that, thanks.

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Milen Lazarov wrote:
On 2007-01-03, Mxsmanic wrote:

Pixel Dent writes:

I think I read this section before; this paragraph sounds familiar. I
always get instructions to "maintain," though. What's the phraseology
when I get a block of altitudes? Or does it even happen with
frequency in real life? How do I request it (or do I even need to
request it)?


From a flight today, west of Billings, MT:

N12345: Unable to maintain 16,000 for turbulence.
ATC: N12345 maintain between 14,000 and 16,000

Yep, we had severe and extreme turbulence pireps near the mountains
today. Bad day to fly anywhere but east from here.

On 2007-01-04, Newps wrote:

Yep, we had severe and extreme turbulence pireps near the mountains
today. Bad day to fly anywhere but east from here.

Yep, the ice was not nice either. Seems that tomorrow will be better
so I might get home. :-)

"Mxsmanic" wrote in message
Now, my question is this: If the FMC has a programmed descent in its
route, do I let the FMC start the descent where it sees fit, or do I
force the aircraft to maintain FL290 until ATC explicitly clears me
for my own navigation or for a lower altitude?

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

And if ATC's last
instruction had simply been "resume own navigation" or "proceed as
filed," would that mean that I'd be free to begin the descent whenever
the FMC (or I) decides it's best?

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

In situations where I can begin the descent at my discretion (assuming
that own navigation implies this), should I tell ATC that I'm leaving
my cruise altitude?

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

If the FMC has a continuously changing estimate
of lower altitudes in the descent profile, what should I give as my
target altitude? The next fix that has a specific altitude? (Such as
a fix in the arrival procedure)

Yes.

Climbing I think I understand. If I'm told to resume own navigation,
or cleared as filed in the first place, I climb per my flight plan/FMC
profile. If ATC says maintain X, I stay at X until ATC tells me to
resume own navigation or instructs me to change altitudes. But the
descent part still has me a bit confused.

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.

D.

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

MCP = max continuous power? Sorry- not familiar with the term as used on an
FMS. The important thing is to not set the altitude hold for descent until
cleared by ATC.

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).

A good center controller will have all of the arrivals spaced like pearls
before everyone hits the arrival's gate. That way everyone can follow the
arrival as charted with ATC isssuing speed changes to maintain spacing.

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?

The most common is a clearance to cross a fix at an assigned altitude
(crossing restriction). Say for example you are cruising at FL290 and the
controller isues you a clearance to cross a fix at 12000'. It is your
perogative as to when to start your descent so long as you cross the fix at
the assigned altitude.

During the climb, ATC sees the final altitude we requested on our flight
plan. They try to get us up there, traffic permitting. After that we request
from ATC any altitude changes we want and they work us to that altitude,
traffic permitting.

What does ATC say if they want you
to follow everything on the plate, including the indicated altitudes?

"DESCEND via the Korry 3"

Did your colleague get into significant trouble?

No, because seperation wasn't lost.

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

Sounds professional.

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

In the IFR world, altitude is all important. There are crossing restrictions
and block altitudes, but most of the time we follow

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?

In the real world we usually follow the arrival procedures with the
altitudes as published. When flying the big jets, just remember that you
will need 3 miles for every 1000' you want to descend plus another 5 miles
to slow for the 250 knot speed restriction at 10000'.

D.