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

John Theune writes:

Are you flying IFR?

Yes. I've filed a SID, a route, and a STAR, and programmed this into
the FMC as well. The FMC apparently decides when to start the descent
from cruise (if you don't override it), presumably based on the
altitude restrictions it has to respect for the arrival procedure.

if so then ATC will tell you what altitude to be at.
Resume own navigation refers to routing not altitude.

Ah ... is there another phrase that also means altitude is at my
discretion, or is altitude always under the control of ATC? The fact
that the FMC provides for its own descent schedule implies that there
must be situations in IFR where I'm allowed to climb or descend at my
discretion (?).

--
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Mxsmanic,

The fact
that the FMC provides for its own descent schedule implies that there
must be situations in IFR where I'm allowed to climb or descend at my
discretion


No. That fact implies that the simulation does not simulate real life
well in this respect. You wanted an example, you got one all by
yourself.

--
Thomas Borchert (EDDH)

Thomas Borchert writes:

That fact implies that the simulation does not simulate real life
well in this respect.

What part of the FMC or ATC simulation is incorrect?

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In a previous article, Mxsmanic said:
if so then ATC will tell you what altitude to be at.
Resume own navigation refers to routing not altitude.

Ah ... is there another phrase that also means altitude is at my
discretion, or is altitude always under the control of ATC? The fact
that the FMC provides for its own descent schedule implies that there
must be situations in IFR where I'm allowed to climb or descend at my
discretion (?).

If your FMC wants to descend, ask ATC for a descent. If you're going to
be descending with multiple segments of different descent rates, ask ATC
for "descent at pilots discretion".

Real world IFR flying is about coordinating your actions with those of all
the other planes out there, not flying along fat, dumb and happy doing
whatever you feel like. That's the whole point of ATC - to make sure you
don't hit what you can't see. ATC's second priority is to make sure the
system runs smoothly, so your actions don't interfere with somebody else
and somebody else's actions don't interfere with you.

--
Paul Tomblin http://blog.xcski.com/
"I love the smell of burning components in the morning.
Smells like victory." (The ******* Operator From Hell)

Paul Tomblin writes:

If your FMC wants to descend, ask ATC for a descent. If you're going to
be descending with multiple segments of different descent rates, ask ATC
for "descent at pilots discretion".

OK, thanks. Is that the procedure followed by pilots in the real
world as well?

Real world IFR flying is about coordinating your actions with those of all
the other planes out there, not flying along fat, dumb and happy doing
whatever you feel like.

Yes. That's why I'm trying to find out what the rules are.

That's the whole point of ATC - to make sure you
don't hit what you can't see. ATC's second priority is to make sure the
system runs smoothly, so your actions don't interfere with somebody else
and somebody else's actions don't interfere with you.

Yes. I try to be cooperative with ATC.

--
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In a previous article, Mxsmanic said:
Paul Tomblin writes:

If your FMC wants to descend, ask ATC for a descent. If you're going to
be descending with multiple segments of different descent rates, ask ATC
for "descent at pilots discretion".

OK, thanks. Is that the procedure followed by pilots in the real
world as well?

I live and fly in the real world, so I can only talk about the real world.
My "real world" is part 91 IFR below the oxygen altitudes, however, so
some of what I say isn't applicablle to part 121 in class A airspace.

Another "trick" is to ask for a cruise clearance, which also allows you to
manage your own descent profile. However in my chunk of the real world,
I've never seen it used or needed it.

I fly with a Garmin 296 handheld GPS. In my experience, nearly always
just around the same time it says I need to start my descent if I want to
descend at 500fpm to my destination, ATC clears me down to a lower
altitude without being asked.

--
Paul Tomblin http://blog.xcski.com/
A male pilot is a confused soul who talks about women when he's flying,
and about flying when he's with a woman.

Paul Tomblin writes:

I fly with a Garmin 296 handheld GPS. In my experience, nearly always
just around the same time it says I need to start my descent if I want to
descend at 500fpm to my destination, ATC clears me down to a lower
altitude without being asked.

I have noticed this as well. I suppose if they know the route well,
they know when the descent usually starts.

--
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In a previous article, Mxsmanic said:
Paul Tomblin writes:
I fly with a Garmin 296 handheld GPS. In my experience, nearly always
just around the same time it says I need to start my descent if I want to
descend at 500fpm to my destination, ATC clears me down to a lower
altitude without being asked.

I have noticed this as well. I suppose if they know the route well,
they know when the descent usually starts.

Except they know where to start my descent whether I'm flying a 100 knot
Archer or a 140 knot Lance, or on one occasion, a Piper Dakota with a 70
knot tail wind.

I suspect there is software they use to handle this.

--
Paul Tomblin http://blog.xcski.com/
#define sizeof(x) ((int)rand()*1024)

Paul Tomblin wrote:

In a previous article, Mxsmanic said:


Paul Tomblin writes:


I fly with a Garmin 296 handheld GPS. In my experience, nearly always
just around the same time it says I need to start my descent if I want to
descend at 500fpm to my destination, ATC clears me down to a lower
altitude without being asked.


I have noticed this as well. I suppose if they know the route well,
they know when the descent usually starts.



Except they know where to start my descent whether I'm flying a 100 knot
Archer or a 140 knot Lance, or on one occasion, a Piper Dakota with a 70
knot tail wind.

I suspect there is software they use to handle this.



It believe it is based on the instrument requirement (?) of 500 fpm rate
of descent.

At a given airspeed and altitude, at 500 fpm an aircraft should commence
its descent at the calculated distance.

This will vary depending on the facility, traffic and procedures.

I calculate the distance in may head for my given cruise altitude and
wait to see if ATC calls me at the appropriate time. They are usually
early on the call to assign lower.