Unclear Clearance

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.

On 11/27/2005 9:30 PM, Daniel Roesen wrote the following:
* Ron Rosenfeld :

From the (US) AIM:


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


Some of that stuff is hard to find but virtually everything
the FAA publishes is available on line. Here is a links
page that has a lot of it:

http://www.clubcherokee.com/links/

Look towards the lower left for the FAA stuff. I find the
searchable FAR database at risingup.com to be particularly
handy.

"Dave Butler" wrote in message
news:1132165254.489969@sj-nntpcache-3...

OK, agreed. I'd call those clearances explicitly discretionary.


I'd call those clearances implicitly discretionary. I'd call a clearance
that included "descend at pilot's discretion" explicitly discretionary.



Yes, exactly. The clearance as originally stated was not for a
discretionary descent. By responding "right" to the pilots question, the
controller amended the clearance and simultaneously demonstrated lack of
understanding of the way clearances are stated. But OK, I see your point.


The controller didn't amend the clearance, she just verified that descent
was at pilot's discretion.

"Daniel Roesen" wrote in message
...

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"?


It means the pilot can begin descent at the time of his choosing and use the
descent rate of his choosing so long as he reaches 11,000 feet not later
than CEDES.



If the latter, does ATC expect a report like "leaving FL240 for 11000" if
not
explicitly requested?


No.



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")?


There is no equivalent standard US phraseology.

"Andrew Sarangan" wrote in message
oups.com...

While flying at 3000 ft, I get a clearance that says "maintain 3000
until established on the localizer, cleared ILS...." If I am already
at 3000, what exactly is the purpose of "maintain 3000"?


To ensure you do not descend below 3000 before you intercept the localizer.



The purpose of the "maintain 3000" is to caution the pilot that the
approach clearance does not imply that he can start descending right
away.

In this context, I take the "maintain 3000 until established" to mean
"maintain at least 3000 until establshed".


So you can climb above 3000? Nope, it means just what it says, 3000 until
established, no more and no less.

"Daniel Roesen" wrote in message
...

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


The AIM can be found online at:

http://www.faa.gov/atpubs/AIM/index.htm



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.


When the descent is to avoid other traffic, as it is whenever "descend now"
is used, quicker is better than slower.