Unclear Clearance

* Steven P. McNicoll :
The controller does not have to state "descend at pilot's discretion" in
order for the descent to be discretionary. A descent clearance with a
crossing restriction is a discretionary descent.

Hm. I'm lacking any real world experience, but in our little wannabe Sim
world (VATSIM) I'm used to crossing restrictions like "XYZ, descend FL120
(to be) level(ed) at FIX" which is to be interpreted as "start descent
now with at least 1000fpm and be at FL120 latest at FIX". This is for
Europe and confirmed to be real-world compatible by several real-world
ATC controllers here. Now I happen to like "flying" in US airspace, where
instructions like "XYZ, cross CEDES at 11000ft" are used. Is that to be
taken analogue to European interpretation to start descending to 11000ft
_now_, or to be taken as "descend 11000ft at own discretion"? If the
latter, does ATC expect a report like "leaving FL240 for 11000" if not
explicitly requested? What is the US equivalent of the European
clearance to "descend now to X with 1000fpm or more, to be level at
FIX"? Is there any at all (short of a full "descend and maintain 11000ft,
1000fpm or more, cross CEDES at level")?

The European expectation of immediate descent with at least 1000fpm v/s
might mean that I do reach 11000ft earlier than CEDES - some folks
argued that "cross X at Y" means that I should carry out my descend so
that I reach the target altitude no later AND NO EARLIER than the fix.
Which would mean that if ATC gives the instruction too early, I would
have to descend with considerably less than 1000fpm, in case the
"cross X at Y" is to be interpreted in this way.

Comments? Insights?


Best regards,
Daniel

On Wed, 23 Nov 2005 03:52:46 +0000 (UTC), Daniel Roesen wrote:

* Steven P. McNicoll :
The controller does not have to state "descend at pilot's discretion" in
order for the descent to be discretionary. A descent clearance with a
crossing restriction is a discretionary descent.

Hm. I'm lacking any real world experience, but in our little wannabe Sim
world (VATSIM) I'm used to crossing restrictions like "XYZ, descend FL120
(to be) level(ed) at FIX" which is to be interpreted as "start descent
now with at least 1000fpm and be at FL120 latest at FIX". This is for
Europe and confirmed to be real-world compatible by several real-world
ATC controllers here. Now I happen to like "flying" in US airspace, where
instructions like "XYZ, cross CEDES at 11000ft" are used. Is that to be
taken analogue to European interpretation to start descending to 11000ft
_now_, or to be taken as "descend 11000ft at own discretion"? If the
latter, does ATC expect a report like "leaving FL240 for 11000" if not
explicitly requested? What is the US equivalent of the European
clearance to "descend now to X with 1000fpm or more, to be level at
FIX"? Is there any at all (short of a full "descend and maintain 11000ft,
1000fpm or more, cross CEDES at level")?

The European expectation of immediate descent with at least 1000fpm v/s
might mean that I do reach 11000ft earlier than CEDES - some folks
argued that "cross X at Y" means that I should carry out my descend so
that I reach the target altitude no later AND NO EARLIER than the fix.
Which would mean that if ATC gives the instruction too early, I would
have to descend with considerably less than 1000fpm, in case the
"cross X at Y" is to be interpreted in this way.

Comments? Insights?



From the (US) AIM:

e. If the altitude information of an ATC DESCENT clearance includes a
provision to "CROSS (fix) AT" or "AT OR ABOVE/BELOW (altitude)," the manner
in which the descent is executed to comply with the crossing altitude is at
the pilot's discretion. This authorization to descend at pilot's discretion
is only applicable to that portion of the flight to which the crossing
altitude restriction applies, and the pilot is expected to comply with the
crossing altitude as a provision of the clearance. Any other clearance in
which pilot execution is optional will so state "AT PILOT'S DISCRETION."

Here are three examples, also from the AIM, which I believe cover the
various nuances:

-----------------------------------
EXAMPLE-
3. "United Four Seventeen, cross Lakeview V-O-R at or above Flight
Level two zero zero, descend and maintain six thousand."

NOTE-
3. The pilot is authorized to conduct descent at pilot's discretion
until reaching Lakeview VOR and must comply with the clearance provision to
cross the Lakeview VOR at or above FL 200. After passing Lakeview VOR, the
pilot is expected to descend at the suggested rates until reaching the
assigned altitude of 6,000 feet.
------------------------------------
EXAMPLE-
4. "United Four Seventeen, cross Lakeview V-O-R at six thousand,
maintain six thousand."

NOTE-
4. The pilot is authorized to conduct descent at pilot's discretion,
however, must comply with the clearance provision to cross the Lakeview VOR
at 6,000 feet.
--------------------------------------
EXAMPLE-
5. "United Four Seventeen, descend now to Flight Level two seven zero,
cross Lakeview V-O-R at or below one zero thousand, descend and maintain
six thousand."

NOTE-
5. The pilot is expected to promptly execute and complete descent to FL
270 upon receipt of the clearance. After reaching FL 270 the pilot is
authorized to descend "at pilot's discretion" until reaching Lakeview VOR.
The pilot must comply with the clearance provision to cross Lakeview VOR at
or below 10,000 feet. After Lakeview VOR the pilot is expected to descend
at the suggested rates until reaching 6,000 feet.
-----------------------------------------

Also, so far as the "proper" rate of descent or climb is concerned:

---------------------
Descend or climb at an optimum rate consistent with the operating
characteristics of the aircraft to 1,000 feet above or below the assigned
altitude, and then attempt to descend or climb at a rate of between 500 and
1,500 fpm until the assigned altitude is reached.
-----------------------------------------

Hope this helps.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

* Ron Rosenfeld :
From the (US) AIM:

Thank you very much for citing the relevant regs. Is this stuff available
online for future reference?

e. If the altitude information of an ATC DESCENT clearance includes a
provision to "CROSS (fix) AT" or "AT OR ABOVE/BELOW (altitude)," the manner
in which the descent is executed to comply with the crossing altitude is at
the pilot's discretion. This authorization to descend at pilot's discretion
is only applicable to that portion of the flight to which the crossing
altitude restriction applies, and the pilot is expected to comply with the
crossing altitude as a provision of the clearance. Any other clearance in
which pilot execution is optional will so state "AT PILOT'S DISCRETION."

OK, that's clear.

Here are three examples, also from the AIM, which I believe cover the
various nuances:

Yep, covered my questions. Thanks.

5. "United Four Seventeen, descend now to Flight Level two seven zero,
cross Lakeview V-O-R at or below one zero thousand, descend and maintain
six thousand."

NOTE-
5. The pilot is expected to promptly execute and complete descent to FL
270 upon receipt of the clearance. After reaching FL 270 the pilot is
authorized to descend "at pilot's discretion" until reaching Lakeview VOR.
The pilot must comply with the clearance provision to cross Lakeview VOR at
or below 10,000 feet. After Lakeview VOR the pilot is expected to descend
at the suggested rates until reaching 6,000 feet.
-----------------------------------------

Also, so far as the "proper" rate of descent or climb is concerned:

---------------------
Descend or climb at an optimum rate consistent with the operating
characteristics of the aircraft to 1,000 feet above or below the assigned
altitude, and then attempt to descend or climb at a rate of between 500 and
1,500 fpm until the assigned altitude is reached.
-----------------------------------------

Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

The most economically way to descend a jet is at near idle thrust,
tactically. But strategically, that's only true if I'm on my computed
economic descent path. So if ATC orders me earlier than reaching my ToD
to "descend now FL270", at what rate do I descend? "optimum rate"
would be very shallow and be not quick enough for the controller who
wants to get me out of the way of something. Should I descend at near
idle thrust? But that would bring me down much quicker than strategically
economic, as I have to fly a longer distance on a suboptimal low flight
level.

I guess this is why in Europe a descent/climb instruction implies
(unwritten rule) "1000fpm or more" - and actually the FMS of a 737NG
seems to do exactly that (at least in the simulation that I have) when
you initiate a VNAV descent earlier than ToD via the "DES NOW"
function. It descends with 1000fpm until it either reaches the target
altitude dialed in the MCP, or it crosses the computed optimum vertical
descent path at which point it raises the rate of descend and lowers
the thrust, in order to maintain the optimum descent path.


Best regards,
Daniel

On Mon, 28 Nov 2005 03:30:59 +0000 (UTC), Daniel Roesen wrote:

Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

Nothing wrong with giving the pilot discretion over the rate of descent.
However, there is a requirement to notify ATC if climb/descent rates will
be less than 500 fpm.


The most economically way to descend a jet is at near idle thrust,
tactically. But strategically, that's only true if I'm on my computed
economic descent path. So if ATC orders me earlier than reaching my ToD
to "descend now FL270", at what rate do I descend? "optimum rate"
would be very shallow and be not quick enough for the controller who
wants to get me out of the way of something. Should I descend at near
idle thrust? But that would bring me down much quicker than strategically
economic, as I have to fly a longer distance on a suboptimal low flight
level.

You seem to be defining "optimum" as equivalent to "economic". I see no
such implication in the US.


I guess this is why in Europe a descent/climb instruction implies
(unwritten rule) "1000fpm or more" - and actually the FMS of a 737NG
seems to do exactly that (at least in the simulation that I have) when
you initiate a VNAV descent earlier than ToD via the "DES NOW"
function. It descends with 1000fpm until it either reaches the target
altitude dialed in the MCP, or it crosses the computed optimum vertical
descent path at which point it raises the rate of descend and lowers
the thrust, in order to maintain the optimum descent path.

Well, Europe has to handle a lot fewer aircraft than does US ATC. So maybe
that's why they need more regulations. But wait, you stated that this is
an "unwritten rule". So it's not a regulation, but merely an expectation.

I would expect that if ATC clears a jet a/c to "descend now" that they
would expect prompt execution and completion of the descent (as stated in
the AIM) and that the rate of descent and so forth would be set out in the
training manuals and possibly the ops specs of the carrier involved.
Again, if it will be less than 500 fpm, the pilot should notify ATC.

The AIM is available on line. Look at www.faa.gov for the publications.
It is not regulatory, but its procedures are generally followed.




Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

* Ron Rosenfeld :
Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

Nothing wrong with giving the pilot discretion over the rate of descent.
However, there is a requirement to notify ATC if climb/descent rates will
be less than 500 fpm.

OK, that makes sense. Never heard of that requirement yet, thanks for
that. Will check our regulations here about comparable requirements.

You seem to be defining "optimum" as equivalent to "economic". I see no
such implication in the US.

Well, what other interpretations of "optimum rate of descend" would
you have in mind? If they didn't have anything specific in mind, they
could have written "any rate consistent with the operating
characteristics". Which would be kinda superfluous as you should never
climb/descend with a rate not being consistent with the operating
characteristics.

My definition of "optimum rate of descend" without further reference to
the parameters for determination of optimality would be something along
the lines of "the minimum rate of descend required to reach a destination
altitude complying to all altitude and speed restrictions as well as
maintaining target speed". This rate is of course a function of time,
with the result being roughly what FMS computes for VNAV as well. :-)

Well, Europe has to handle a lot fewer aircraft than does US ATC. So
maybe hat's why they need more regulations. But wait, you stated that
this is an "unwritten rule". So it's not a regulation, but merely an
expectation.

Yep. But compliance with that is quite universally as far as I'm told by
controllers. :-)

The AIM is available on line. Look at www.faa.gov for the publications.
It is not regulatory, but its procedures are generally followed.

Thanks!


Best regards,
Daniel

On Mon, 28 Nov 2005 06:35:53 +0000 (UTC), Daniel Roesen
wrote:

* Ron Rosenfeld :
Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

Nothing wrong with giving the pilot discretion over the rate of descent.
However, there is a requirement to notify ATC if climb/descent rates will
be less than 500 fpm.

OK, that makes sense. Never heard of that requirement yet, thanks for
that. Will check our regulations here about comparable requirements.

You seem to be defining "optimum" as equivalent to "economic". I see no
such implication in the US.

Well, what other interpretations of "optimum rate of descend" would
you have in mind? If they didn't have anything specific in mind, they
could have written "any rate consistent with the operating
characteristics". Which would be kinda superfluous as you should never
climb/descend with a rate not being consistent with the operating
characteristics.


I typically climb in the neighborhood of a 1000 fpm and descend
between 800 and 1200 fpm.

If I have a descent to and cross at, I'll adjust the rate of descent
to get me down within a mile or two of the crossing point.
However if I'm kept "up there" too long, I'm not going to blow my, or
my passengers ear drums with too fast a descent.

If I'm at cruise, backing off on the throttle 5" will give me 500 fpm
while the speed stays constant. If need be I can slow down a *bit*
which will give me a steeper descent yet.

However I prefer to keep the descent to about 800 and calculate how
far out I need to start down. If I'm within a minute or two of my
limits I'll call ATC and request to start down.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
My definition of "optimum rate of descend" without further reference to
the parameters for determination of optimality would be something along
the lines of "the minimum rate of descend required to reach a destination
altitude complying to all altitude and speed restrictions as well as
maintaining target speed". This rate is of course a function of time,
with the result being roughly what FMS computes for VNAV as well. :-)

Well, Europe has to handle a lot fewer aircraft than does US ATC. So
maybe hat's why they need more regulations. But wait, you stated that
this is an "unwritten rule". So it's not a regulation, but merely an
expectation.

Yep. But compliance with that is quite universally as far as I'm told by
controllers. :-)

The AIM is available on line. Look at www.faa.gov for the publications.
It is not regulatory, but its procedures are generally followed.

Thanks!


Best regards,
Daniel

On Mon, 28 Nov 2005 06:35:53 +0000 (UTC), Daniel Roesen wrote:

Well, what other interpretations of "optimum rate of descend" would
you have in mind? I

I would take it to mean that you take into account all the factors
involved, not just how much money you're going to spend/save. That would
include, but not be limited to, operating characteristics of the aircraft,
passenger comfort, ATC expectations, expense, visibility at the required
angle of attack, etc.

For example, in my Mooney, I would typically use a cruise climb of 115-120
KIAS rather than a best rate of climb of about 90 KIAS because of improved
forward visibility at the lower AOA (unless ATC requested "best rate").




Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Well, what other interpretations of "optimum rate of descend" would
you have in mind?

Depends what one is trying to optimize. Money, turbulence, time
enroute, arrival time (to coincide with an open gate), dive currency,
there are many things that one can attempt to "optimize", though I'd
agree that ATC is not likely to think of them all.

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.

"Daniel Roesen" wrote in message
...
* Ron Rosenfeld :
Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

Nothing wrong with giving the pilot discretion over the rate of descent.
However, there is a requirement to notify ATC if climb/descent rates
will
be less than 500 fpm.

OK, that makes sense. Never heard of that requirement yet, thanks for
that. Will check our regulations here about comparable requirements.

You seem to be defining "optimum" as equivalent to "economic". I see no
such implication in the US.

Well, what other interpretations of "optimum rate of descend" would
you have in mind? If they didn't have anything specific in mind, they
could have written "any rate consistent with the operating
characteristics". Which would be kinda superfluous as you should never
climb/descend with a rate not being consistent with the operating
characteristics.

I believe FAAO 7110.183 has all the performance expectations for various
aircraft from ATC's perspective. Good luck finding it.. I have a 6 year old
version and cant find it online right now.




--
Mike Teague - Vancouver WA, USA
-- Opie and Anthony - XM202 - O&A Party Rock!
-- Phil Hendrie = Radio Genius

"Mike Teague" wrote in message
news
"Daniel Roesen" wrote in message
...
* Ron Rosenfeld :
Hm... interesting. "optimum rate consistent with the operating
characteristics of the aircraft". This is fuzzy.

Nothing wrong with giving the pilot discretion over the rate of
descent.
However, there is a requirement to notify ATC if climb/descent rates
will
be less than 500 fpm.

OK, that makes sense. Never heard of that requirement yet, thanks for
that. Will check our regulations here about comparable requirements.

You seem to be defining "optimum" as equivalent to "economic". I see
no
such implication in the US.

Well, what other interpretations of "optimum rate of descend" would
you have in mind? If they didn't have anything specific in mind, they
could have written "any rate consistent with the operating
characteristics". Which would be kinda superfluous as you should never
climb/descend with a rate not being consistent with the operating
characteristics.

I believe FAAO 7110.183 has all the performance expectations for various
aircraft from ATC's perspective. Good luck finding it.. I have a 6 year
old
version and cant find it online right now.



Ahh, I found it, sorry, it's now appendix A in the 7110.65.

--
Mike Teague - Vancouver WA, USA
-- Opie and Anthony - XM202 - O&A Party Rock!
-- Phil Hendrie = Radio Genius