losing altitude in holding pattern

[gismo]

Since there are a number of different ways to do a PT and the size of it depends, to a degree, on the speed of the airplane and the wind, it would be hard to depict one accurately. However, maybe they could depict the maximum size it should be. I do agree that if the maximum size PT would take you outside the ring it should be shown crossing it.

Perhaps. But since I've never seen anything that indicates the PT depiction was intended to show it's maximum extent, that seems useless to me. What I'd rather know is the extent of the protected area around the PT but that would probably clutter things up so much as to make things worse overall. Consider how they are drawn with a in/out course line plus a 45° "barb". Would you have the tip of the barb represent the furthest point of the PT from it's origin or would that be located at the joint between the in/out course and the barb? The former would be weird given the offset from the course line and the latter would leave the tip of the barb further away from the origin than the specified max distance. Keep in mind that aside from the in/out course direction, the standard PT depiction is merely symbolic of what's actually expected in terms of a flight path.

I also think that when the fix that the distance is measured from could be ambiguous they should state what is is, just like Jepp. The fact that the majority of the people here were mistaken or unsure is a statement about the clarity of the charts. Sure we figured it out at the end which is a good academic exercise but that's not what charts are for. They should be able to be interpreted correctly the first time you read them.

Beware the law of unintended consequences. Removing the numerical radius of the scale circle might not be such a good idea. While I can't come up with a clear benefit to printing the scale circle radius I do believe that it's at least somewhat useful in that it defines the chart scale much like the scale ruler you often see on maps or the bottom of a sectional. Rather than have it eliminated I'd suggest fixing the ambiguity of the "remain within" origin. One way would be to do as Jeep does i.e. print the fix name with the distance if there's any chance
of misinterpretation. Another would be to include something in the legend stating that this distance always refers to the fix at the start of the heavy course line in the profile view. It might also be helpful to put another note in the legend describing the scale circle along with what it does and doesn't indicate.

 

[Everskyward]

Perhaps. But since I've never seen anything that indicates the PT depiction was intended to show it's maximum extent, that seems useless to me. What I'd rather know is the extent of the protected area around the PT but that would probably clutter things up so much as to make things worse overall. Consider how they are drawn with a in/out course line plus a 45° "barb". Would you have the tip of the barb represent the furthest point of the PT from it's origin or would that be located at the joint between the in/out course and the barb? The former would be weird given the offset from the course line and the latter would leave the tip of the barb further away from the origin than the specified max distance. Keep in mind that aside from the in/out course direction, the standard PT depiction is merely symbolic of what's actually expected in terms of a flight path.

I was only throwing that out there as a possible solution for what Felix wanted but I agree that it's only a symbolic description and it would be impossible to make it accurate.

Removing the numerical radius of the scale circle might not be such a good idea. While I can't come up with a clear benefit to printing the scale circle radius I do believe that it's at least somewhat useful in that it defines the chart scale much like the scale ruler you often see on maps or the bottom of a sectional.

I don't see why you need the circle to begin with. Why can't the whole chart be to scale except in certain circumstances where they could write "not to scale". Jepp charts don't have that circle and they have the scale ticks on the side like you say.

I know that I am biased because I have always used Jepp charts but I'm perhaps even more biased now.

 

[sba55]

I was only throwing that out there as a possible solution for what Felix wanted but I agree that it's only a symbolic description and it would be impossible to make it accurate.

Well, IMO, the main problem I'd like to fix _somehow_ is that the current NACO plates are simply wrong. They claim that everything within the circle is to scale, but the PT is not only not to scale, it's depicted in a way that is impossible given the "remain within" distance.

I don't see why you need the circle to begin with. Why can't the whole chart be to scale except in certain circumstances where they could write "not to scale". Jepp charts don't have that circle and they have the scale ticks on the side like you say.

I know that I am biased because I have always used Jepp charts but I'm perhaps even more biased now.

I agree with that. Less clutter would be excellent.

 

[Palmpilot]

Well, IMO, the main problem I'd like to fix _somehow_ is that the current NACO plates are simply wrong. They claim that everything within the circle is to scale, but the PT is not only not to scale, it's depicted in a way that is impossible given the "remain within" distance.

I'm not sure that NACO claims that "everything" is to scale within the circle.

If the arrow were a depiction of the actual flight path, then the point where the arrow ends could have some meaning, but it's not, so scale has no applicability to it. It's just an indication of which side you're supposed to make the turn on.

 

[olasek]

In my opinion the largest source of confusion is drawing the PT "barb" very close to the perimeter of the circle (in case of KALM). Looking at this circle and then appreciating how PT 'stretches' and then remembering that everything inside is supposed to be 'to scale' is simply a very powerful visual statement to a pilot. All other suggestions are great but as a first order of business folks at NACO should consider drawing the PT so it would also be 'to scale'.

 

[sba55]

I'm not sure that NACO claims that "everything" is to scale within the circle.

If the arrow were a depiction of the actual flight path, then the point where the arrow ends could have some meaning, but it's not, so scale has no applicability to it. It's just an indication of which side you're supposed to make the turn on.

I'm not talking about the arrows, though. The problem is that the PTs are depicted way outside - at least 4 NM in this case - of where they could possibly be.

So while I agree that the PT depiction isn't something that's supposed to be to scale, showing the entire PT way outside where it could be given the "remain within" restriction is highly misleading.

 

[Palmpilot]

Getting back to the original question, I think I would fly this approach by descending at 1000 fpm, which is what I was taught to use for non-precision approaches until 200 feet above the MDA for whatever segment I was on. Normally, that would involve being outbound for two minutes, on the 45 for one minute, making a 180 for one minute, and about a minute to get back to the point where the 45 started. That's five minutes, enough to get down to 7000 feet. Then I'd have another 1200 feet to lose, preferably by the time I reached the FAF. The problem, as we've discovered, is that the PT fix is four miles closer to the airport than the FAF, so if I started my outbound timing at the PT fix, I would probably still be at about 7000 feet at the FAF inbound.

Instead, I think I would take advantage of the statement in AIM 5-4-9a1 that "the point at which the turn may be commenced and the type and rate of turn is left to the discretion of the pilot (limited by the charted remain within xx NM distance)," by starting my turn at 6 DME instead of using timing. At 90 knots, that would have me down to 8000 at the point of starting the 45, and the three minutes or so to get back to that point headed inbound would be more than enough to descend the additional 2200 feet I would need to lose by the time of reaching the FAF inbound. In addition, I would be established on the final approach course more than two NM outside the FAF.

 

[olasek]

Richard,

On one hand you say 1000 ft/min on the other you are talking about 90 kts. In my opinion and per my experience these two numbers are simply incompatible in a typical light GA aircraft (flaps up) and especially in those modern very slippery fiberglass constructions. You would be doing a lot more than 90 kts at full idle while descending at 1000 ft/min. And by the way your 1000 ft/min and 90 kts are simply incompatible in terms of what descend gradient is required during approach. Someone mentioned it in the beginning of this thread and the number sounds right that no controller would ask you to descend steeper than 400 ft/nm which is roughly a 1:15 gradient (a typical 3 deg GS is around 1:20), so it is not hard to calculate that for 1000 ft/min it would mean TAS of around 150 kts, anything slower and you are VERY steep.

By the way, sticking with this steepest gradient of 1:15 or equivalently 400 ft/nm it is not hard now to calculate if it is doable in the case of this KALM VOR-DME approach with restriction of remaining within 10 nm of the VOR. If we make all calculations it turns out it is doable but you will have to maintain the descent gradient close to this max value of 1:15 throughout the whole approach - assuming you start at VOR at 12000 and want to hit the MDA of 4460 at the end.

 

[Palmpilot]

On one hand you say 1000 ft/min on the other you are talking about 90 kts. In my opinion and per my experience these two numbers are simply incompatible in a typical light GA aircraft (flaps up) and especially in those modern very slippery fiberglass constructions. You would be doing a lot more than 90 kts at full idle while descending at 1000 ft/min.

Not in the planes I fly. I generally don't even need to pull power to idle. I might need to put in ten degrees of flaps in a Skylane if I wanted to limit my speed to 90 knots, but not in a Skyhawk. In a Cutlass or Cardinal, I would put the gear down when I started the descent.

Of course, the planning would need to be different in faster airplanes.

And by the way your 1000 ft/min and 90 kts are simply incompatible in terms of what descend gradient is required during approach. Someone mentioned it in the beginning of this thread and the number sounds right that no controller would ask you to descend steeper than 400 ft/nm which is roughly a 1:15 gradient (a typical 3 deg GS is around 1:20), so it is not hard to calculate that for 1000 ft/min it would mean TAS of around 150 kts, anything slower and you are VERY steep.

The requirements on ATC do not restrict the descent rate that the pilot is allowed to use.

As for the descent gradient being very steep, that's why I was taught to reduce to 500 fpm by 200 feet above my target altitude.

By the way, sticking with this steepest gradient of 1:15 or equivalently 400 ft/nm it is not hard now to calculate if it is doable in the case of this KALM VOR-DME approach with restriction of remaining within 10 nm of the VOR. If we make all calculations it turns out it is doable but you will have to maintain the descent gradient close to this max value of 1:15 throughout the whole approach - assuming you start at VOR at 12000 and want to hit the MDA of 4460 at the end.

I prefer to get down to the MDA of the intermediate segment +100/-0 by the time I reach the FAF inbound. (If I'm going to do any heroics, I prefer to do them up high.) So that would give me 16 nm to descend 6200 feet (ten nm out and six nm back). If I used up the whole 16 nm, that would require a descent gradient of 388 ft/nm. Personally, I would prefer NOT to use up the entire protected area, so I would want to descend steeper than that. Even 400 ft/nm would use up 15.5 nm out and back. I know the approach requires DME, but estimating where to begin the turn so as to not eat up a 0.25 nm buffer from the edge of the protected area is living kind of dangerously in my book. 500 ft/nm would require 12.4 nm across the ground, which is starting to look like a margin that I would be comfortable with. At 90 knots, 500 ft/nm is 750 fpm; at 120 knots, it's 1000 fpm. At 160 knots (nearly the category D limit), it would require 1333 fpm.

Maybe this is not a well-designed approach.

 

[TangoWhiskey]

Well, IMO, the main problem I'd like to fix _somehow_ is that the current NACO plates are simply wrong. They claim that everything within the circle is to scale, but the PT is not only not to scale, it's depicted in a way that is impossible given the "remain within" distance.

Yeah, it would be good for them to update the Introduction to IAP Symbols document to make it clear what data is drawn to scale, and which is not.

Here's what they have to say about it:

 

[olasek]

Unfortunately the statement only the data within the reference circle is drawn to scale is fraught with ambiguities since for any reasonable person this would most likely suggest that ALL data within the circle is drawn to scale.

 

[TangoWhiskey]

OK, I told you that I had written to them. My suggestion was that NACO charts include the PT fix name next to the profile view's "remain within xx nm" comment, like the Jepp charts do, to eliminate any possible confusion. I included a link to this thread so he could review our comments/discussion. Here's the reply I received this morning:

Thanks for your recommendation. The government charting standards for
instrument approach procedures are a collaborative effort between the
Department of Transportation (DOT/FAA) and the Department of Defense (DOD),
since both produce government agencies issue instrument approach charts.
The recommendation you have submitted will have to be reviewed by these
organization to acceptability.

I have read the discussions concerning the procedure in question at
Alamogordo, NM. The Procedure Turn on this approach is to remain within 10
NM of BOLES (BWS) VOR. BOLES VOR is readily identified as the PT fix since
it is labeled as the "IAF" (initial approach fix). The "REMAIN WITHIN 10
NM" note placed at the end of the solid line emanating from the PT fix
(IAF) is always the distance from the IAF/PT fix.

Information concerning procedure turn requirements can be found in the
Airmen's Information Manual (AIM), paragraph 5-4-9, and in the Instrument
Procedures Handbook (IPH), on pages 5-38 through 5-40. The AIM can be found
at the following website:

http://www.faa.gov/air_traffic/publications/

The IPH can be found at the following website:

http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/media/CH-05.pdf

The 10 NM ring is centered on PAYNE. In the FAA Aeronautical Chart Users
Guide, under the section on Terminal Procedures Publication on Page 53, and
in the PLANVIEW section, it describes the use of the 10 NM ring. It is as
follows:

To help explain some of the chart symbols and their purpose, it would be
best is all participants would go to the following website where they can
access the FAA Aeronautical Chart Users Guide:

http://avn.faa.gov/index.asp?xml=aeronav/applications/digital/aero_guide

Toward the bottom of the site you will see "Introduction To IAP Chart
Symbols" and "IAP Chart Symbols". Both of these guides provide every
example of chart symbols and their meanings.

If I can be of further assistance, please don't hesitate to contact me.

Brad W. Rush
National Aeronautical Navigation Services
(AeroNav Services)
Regulatory Support Team
405-954-0188

 

[TangoWhiskey]

Referencing the Planview comment/snippet from Mr. Rush's reply, one thing stood out and surprised me: "data both within and without the circle is drawn to scale"...

Why have the scale circle at all then, if that's true?

 

[sba55]

Referencing the Planview comment/snippet from Mr. Rush's reply, one thing stood out and surprised me: "data both within and without the circle is drawn to scale"...

Why have the scale circle at all then, if that's true?

Well, in that case, things are even more confusing. Why not just have the circle be the "remain within 10 (or 15, etc.) NM" reference? Or maybe this means that everything on the plate is drawn to scale unless those charting devices are used, in which case only things within the circle are drawn to scale?

Btw., I think it's great that they're so responsive. Pretty amazing for a govt agency....

 

[olasek]

Nice that he replied and even hinted he read the thread. But he is clearly missing the meat of the discussion. Quite amazingly he states that the purpose of the circle is to provide only the sense of scale and distance yet it is precisely this lack of scale in case of the PT that is at issue here.

 

[flyingcheesehead]

Btw., I think it's great that they're so responsive. Pretty amazing for a govt agency....

NACO has always been extremely responsive and courteous IME. I've been impressed with every interaction I've had with them. I'm glad they're so helpful, they serve a very important safety function and it's good to know there's good people running the place.

 

[TangoWhiskey]

The February 2011 issue of IFR (going to press this week) will have an article on this subject, inspired by this thread. No, I didn't write it... but if I did the proceeds if any would have gone to POA's server thread. I'll be interested on the author's take on the topic.

 

[Palmpilot]

The article is out. They say that on FAA charts, you have to look at the profile view to find out which is the PT fix, and you do it by following the black line back from the PT to the last marked fix.

They also discuss the draconian descent requirement, pointing out that it takes planning on this approach.

 

[TangoWhiskey]

The article is out. They say that on FAA charts, you have to look at the profile view to find out which is the PT fix, and you do it by following the black line back from the PT to the last marked fix.

They also discuss the draconian descent requirement, pointing out that it takes planning on this approach.

Page 18; just pulled my copy out of the frozen mailbox.

 

[Palmpilot]

By the way, thanks for bringing this to IFR Magazine's attention. Considering the widespread confusion on this, it's really something that needs to be publicized.

 

[denverpilot]

Interestingly enough, I can confirm that there were at least a couple of questions on my recent Instrument Written regarding this thread's topic.

Someone at FAA must have decided it was important enough to start floating the concepts of the difference between the ring and the IAF that were covered here into the test pool.

Whether they were in the "real" test pool, or the "we're floating some questions to see how people do" pool, I couldn't tell you. The CATS system said there were 2 additional questions floated to me in the top left that weren't counted toward my overall score.

(They apparently do this so you don't freak out that you have more questions than you expected to have. But they don't tell you which ones were the "floaters".)