Circling radius and obstacle clearnce.

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John777

Pre-takeoff checklist
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For large aircraft like category D/E has 2.3 /4.5nm circling radius, whereas Category B aircraft is only 1.5nm from the end of the runways. Now my question is, if I go more than 1.5nm and stay within 2.3 or 4.5nm, provided their circling minimums are the same, am I technically still assured of obstacle clearance?
 
John777 said:
For large aircraft like category D/E has 2.3 /4.5nm circling radius, whereas Category B aircraft is only 1.5nm from the end of the runways. Now my question is, if I go more than 1.5nm and stay within 2.3 or 4.5nm, provided their circling minimums are the same, am I technically still assured of obstacle clearance?
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Not at Cat A minimums.
 
MAKG1 said:
Aeronautical Information Manual.
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I guess you are referring to the Chapter 5 of the AIM, can you specify the subsection if you do not mind?
Thanks.
 
IF the minimums are the same for the higher Cats, then yes, you are assured of obstacle clearance.

Random example - Blythe, CA KBLH, RNAV (GPS) RWY 26:

https://skyvector.com/files/tpp/1612/pdf/00053R26.PDF

If you are Cat A (or B as in your question) and you descend to 2060 for the Circling MDA, but swing out wide into the C or D area (where the MDA is also 2060), then yes, you still have at least the same obstacle clearance you did in the Cat A or B area. How would it be less?

However, if you swing out wide, then you also should make sure you have enough visibility to keep the airport environment in sight.

Now, if the Circling MDAs increase as the Category increases, the story is obviously different. Take Prescott, AZ, KPRC, VOR RWY 12 as another random example:

https://skyvector.com/files/tpp/1612/pdf/00546V12.PDF

If you're Cat B with 5580 for the MDA, and you go out into the Cat D area with 5940 MDA (but stay at 5580), chances are good that not only won't you have enough obstacle clearance but will actually be below the obstacles (mountains, antennas) at that altitude. Not good!

Stay within the established radius. There should be no reason not to, especially with the new, increased circling radii for the higher Categories. And if you can't due to some unusual reason, maybe the best move is to go missed approach and try again.
 
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John777 said:
Yeah, I am going to look up FAA order 8260.3B for that.
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It 8260.3C now. The new circling criteria radii increase with the elevation of the airport. There is a nice table in pilot-speak in the FAA legend for approach charts.
 
Interesting fact I found out from the Order was, We can still go missed at MDA before hitting MAP but no turns...
Is there any other reference other than the FAA Order?
 
John777 said:
Interesting fact I found out from the Order was, We can still go missed at MDA before hitting MAP but no turns...
Is there any other reference other than the FAA Order?
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You could always do that, couldn't you?

How many references do you need?
 
Greg Bockelman said:
You could always do that, couldn't you?

How many references do you need?
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But when I was doing my training, I was taught to hold MDA until MAP and go missed. I mean, there still can be a chance to break out of thr clouds and see the runway and land, but you do not want to get close to runway when you are still 500-700ft above.
 
John777 said:
But when I was doing my training, I was taught to hold MDA until MAP and go missed. I mean, there still can be a chance to break out of thr clouds and see the runway and land, but you do not want to get close to runway when you are still 500-700ft above.
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Yeah, that is kind of old school. The better way of doing that is to compute a visual descent point from which a normal descent and landing can be made. Once you pass that point, you know a landing really isn't possible so start the climb at that point knowing you have to continue to the MAP before making a turn.
 
In other words, yeah, you might see the runway when you get closer, but if you are not in a position to make a normal descent and landing, a missed approach is required.
 
Greg Bockelman said:
In other words, yeah, you might see the runway when you get closer, but if you are not in a position to make a normal descent and landing, a missed approach is required.
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My another question is, when ATC gives the heading to fly after takeoff, I usually start turning at 400ft because the obstacle clearance starts at 2nm beyond the end of the runway, is there any regulation regarding this?
 
John777 said:
My another question is, when ATC gives the heading to fly after takeoff, I usually start turning at 400ft because the obstacle clearance starts at 2nm beyond the end of the runway, is there any regulation regarding this?
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Where's your CFII for all of these questions? I'm honestly getting curious. If you're just a sim pilot just say it, there's no harm and we won't look down on you.
 
Ryanb said:
Where's your CFII for all of these questions? I'm honestly getting curious. If you're just a sim pilot just say it, there's no harm and we won't look down on you.
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I've previously been of the opinion that we've been duped into doing some kid's homework, or he's a troll having fun, or a sim guy, etc etc. Even if the answers to the questions are interesting at times, it's hard to for me to put forth the effort for someone that's not also interested in putting something back into the PoA community. This guy is a one way valve.

But you just got me thinking...John777 mentioned his academy and SOPs. Now I don't have experience at a pilot mill like that, but perhaps the students don't get the kind of direct relationship with their instructor that we take for granted at a more traditional flight school. Combine that with a bunch of instructors that are presumably there to get their 1500 and get out, then maybe John777 is in a situation where he genuinely wants to learn this stuff, but is stuck in a learning environment where he's told to focus only on what he needs for the ride and nothing more.

I just wish he'd tell us.
 
kayoh190 said:
I've previously been of the opinion that we've been duped into doing some kid's homework, or he's a troll having fun, or a sim guy, etc etc. Even if the answers to the questions are interesting at times, it's hard to for me to put forth the effort for someone that's not also interested in putting something back into the PoA community. This guy is a one way valve.

But you just got me thinking...John777 mentioned his academy and SOPs. Now I don't have experience at a pilot mill like that, but perhaps the students don't get the kind of direct relationship with their instructor that we take for granted at a more traditional flight school. Combine that with a bunch of instructors that are presumably there to get their 1500 and get out, then maybe John777 is in a situation where he genuinely wants to learn this stuff, but is stuck in a learning environment where he's told to focus only on what he needs for the ride and nothing more.

I just wish he'd tell us.
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My thoughts exactly. I've been thinking this for quite some time. There is rarely ever a response when you try to ask him a question other than what his thread pertains to. It's hard for me to imagine that he has an instructor who is so absentminded to not give him adequate knowledge. POA doesn't serve as a CFI(I) replacement it's just a supplement. I'd love to hear more about his situation.
 
I'm not convinced he's even a Private Pilot based upon his non-IFR related questions.
 
John777 said:
May be my academy wanted us to get closer to the runway in a hope to see the runway... But I got to follow our SOPs here ecorrect?
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I don't know what the school's reason is for not wanting you to start a climb before the MAP, but while you're at that school it's probably easiest to do things the way they want them done (as long as it's legal and not putting you in danger). However it's important to realize that once you get to a point where it's no longer possible to land "at a normal rate of descent using normal maneuvers," then 14 CFR 91.175(c)(1) prohibits you from descending below DA/DH or MDA. (And by the way, even if you do start the climb early, for a missed approach that requires a turn, don't start the turn early.)
 
RussR said:
...However, if you swing out wide, then you also should make sure you have enough visibility to keep the airport environment in sight....
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Yes. Even though the MDAs are the same on that chart, the visibility minimums are higher for the higher categories.
 
John777 said:
Interesting fact I found out from the Order was, We can still go missed at MDA before hitting MAP but no turns...
Is there any other reference other than the FAA Order?
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A reference that applies to pilots is 14 CFR 91.175(a), which says, among other things, that "Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97 of this chapter for that airport."

The approach procedure is depicted on the chart, and it specifies the courses and altitudes to fly. As long as the altitude is depicted as a minimum altitude, then you are allowed to fly higher than that (because that's what "minimum" means). However if you deviate from the depicted course, then you're no longer using the approach procedure, which puts you in violation of the regulation above (unless you are doing so in response to an ATC instruction).
 
Palmpilot said:
A reference that applies to pilots is 14 CFR 91.175(a), which says, among other things, that "Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97 of this chapter for that airport."

The approach procedure is depicted on the chart, and it specifies the courses and altitudes to fly. As long as the altitude is depicted as a minimum altitude, then you are allowed to fly higher than that (because that's what "minimum" means). However if you deviate from the depicted course, then you're no longer using the approach procedure, which puts you in violation of the regulation above (unless you are doing so in response to an ATC instruction).
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While it's not common to have maximum altitudes on instrument approaches, they do exist. All of the northwest approaches into Oakland top out at 1800 at the FAFs, for instance. The reason is San Francisco's approaches to the 19s, which are just above that.

An early climb on those approaches might be problematic, at least above 1800. Note that some of those approaches have maximum altitudes charted on the missed (at 1600, not 1800), but the VOR 10R doesn't. So, what do you do if you decide to go missed just past the FAF?
 
MAKG1 said:
While it's not common to have maximum altitudes on instrument approaches, they do exist. All of the northwest approaches into Oakland top out at 1800 at the FAFs, for instance. The reason is San Francisco's approaches to the 19s, which are just above that.

An early climb on those approaches might be problematic, at least above 1800. Note that some of those approaches have maximum altitudes charted on the missed (at 1600, not 1800), but the VOR 10R doesn't. So, what do you do if you decide to go missed just past the FAF?
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That's why I was careful to write "As long as the altitude is depicted as a minimum altitude..." When either a mandatory altitude or a maximum altitude is depicted, then you have to comply with those.
 
Palmpilot said:
That's why I was careful to write "As long as the altitude is depicted as a minimum altitude..." When either a mandatory altitude or a maximum altitude is depicted, then you have to comply with those.
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There is still a question, particularly for the VOR 10R approach, as to what the maximum is between the FAF and MAP. As charted, it suggests 1800 at the FAF and FL600 afterward. Given the SFO 19R/19L approaches overhead have minimums of 2800, that seems wrong, and any climb above 1800 past the FAF would be problematic, resulting in TCAS RAs. For the other approaches, like the ILS 12, a DESCENT to 1600 is called for if one decides to go missed right after the FAF.
 
MAKG1 said:
There is still a question, particularly for the VOR 10R approach, as to what the maximum is between the FAF and MAP. As charted, it suggests 1800 at the FAF and FL600 afterward. Given the SFO 19R/19L approaches overhead have minimums of 2800, that seems wrong, and any climb above 1800 past the FAF would be problematic, resulting in TCAS RAs.
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I don't think it's wrong in the sense of violating any rule. If starting a missed approach climb after the FAF caused a conflict, ATC would have to manage the situation, but in the interest of safety, staying at or below 1800 until reaching the MAP might be the wisest action. :dunno:

For the other approaches, like the ILS 12, a DESCENT to 1600 is called for if one decides to go missed right after the FAF.
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Yeah, it does look that way, all right.
 
CAT B mins are 1.7 for approach procedures surveyed under the late-2012 circling radii revisions. The radii for CAT B and other categories actually increase depending on the MSL altitude of the MDA. This is all highlighted in AIM Figure 5-4-27 and 5-4-28.
 
aterpster said:
It 8260.3C now. The new circling criteria radii increase with the elevation of the airport. There is a nice table in pilot-speak in the FAA legend for approach charts.
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This is a small technicality, but the radii increase with the MSL altitude of the circling minima. This distinction is important at airports like Santa Monica (SMO) which have circling mins at over 1,000' AGL.
 
Harold Rutila said:
This is a small technicality, but the radii increase with the MSL altitude of the circling minima. This distinction is important at airports like Santa Monica (SMO) which have circling mins at over 1,000' AGL.
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The obstacle evaluation uses the true airspeed 1,000 feet above the airport elevation. That doesn't mean the circling MDA will be 1,000 feet above the airport elevation. It's an TAS approximation. TAS varies with temperature in the real world. These criteria are a whole lot better than what we had previously. The maneuvering area the specialist evaluates will be predicated on that true airspeed. On one extreme if no significant obstacles are found, 300 feet will be added to whatever is found, and the standard circle to land MDAs will be used. (8260.3C, Table 3-2-1) On the other extreme, the circle to land MDA could be much greater than 1,000 feet Height Above Airport.
 
aterpster said:
The obstacle evaluation uses the true airspeed 1,000 feet above the airport elevation. That doesn't mean the circling MDA will be 1,000 feet above the airport elevation. It's an TAS approximation. TAS varies with temperature in the real world. These criteria are a whole lot better than what we had previously. The maneuvering area the specialist evaluates will be predicated on that true airspeed. On one extreme if no significant obstacles are found, 300 feet will be added to whatever is found, and the standard circle to land MDAs will be used. (8260.3C, Table 3-2-1) On the other extreme, the circle to land MDA could be much greater than 1,000 feet Height Above Airport.
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Very interesting. Thanks for the explanation.
 
Harold Rutila said:
Very interesting. Thanks for the explanation.
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Thanks.
by the way, which section of the AIM states that Category A minimums does not count for obstacle clearance for other categories?
 
John777 said:
Thanks.
by the way, which section of the AIM states that Category A minimums does not count for obstacle clearance for other categories?
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It may not have occurred to the authors of the AIM that anyone would think that Category A minimums would apply to anything other than Category A aircraft. You might be tempted to say that they should count if the higher category aircraft stays within the category A circling distance, but that probably would require excessive bank angles, because a faster aircraft is going to have a wider turning radius for a given bank angle.
 
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By the way, I could be wrong, but my understanding is that even if you're flying an aircraft that would normally be flown faster, if you fly the circling maneuver within the category A speed limitation and remain within the category A circling radius (and are able to do so safely), then you can use category A minimums.
 
Palmpilot said:
By the way, I could be wrong, but my understanding is that even if you're flying an aircraft that would normally be flown faster, if you fly the circling maneuver within the category A speed limitation and remain within the category A circling radius (and are able to do so safely), then you can use category A minimums.
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Abnormally slow approach or circling speeds is a rather unsafe way to perform an already dangerous maneuver.
 
MAKG1 said:
Abnormally slow approach or circling speeds is a rather unsafe way to perform an already dangerous maneuver.
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Dangerous! :eek: Gheesh you're sounding like that Iceman character!

Not if you know what you're doing and are competent. Done it with turbo props and jets, as well as GA planes. YMMV
 
mscard88 said:
Dangerous! :eek: Gheesh you're sounding like that Iceman character!

Not if you know what you're doing and are competent. Done it with turbo props and jets, as well as GA planes. YMMV
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Statistics have shown the "classic" CTL can be quite hazardous, particularly at night and/or in rain or snow. The FAA decided many years ago to prohibit Part 121 CTL unless specific training was provided. It was a lot easier in a DC-6B than in a 707. American Airlines demonstrated that at KCVG.

When TWA operated out of KMKC, CTL was legal and required to land on Runway 36. I rode the jump seat of a 707-300 that did it. Not very comfortable.
 
Palmpilot said:
By the way, I could be wrong, but my understanding is that even if you're flying an aircraft that would normally be flown faster, if you fly the circling maneuver within the category A speed limitation and remain within the category A circling radius (and are able to do so safely), then you can use category A minimums.
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No, you cannot select a lower category, only a higher category.
 
MAKG1 said:
Abnormally slow approach or circling speeds is a rather unsafe way to perform an already dangerous maneuver.
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It's a question of degree. A 182 can be flown safely in either category A or category B speed ranges, for example. There's no way a 747 could. That's why I included the condition "and are able to do so safely."
 
Palmpilot said:
It's a question of degree. A 182 can be flown safely in either category A or category B speed ranges, for example. There's no way a 747 could. That's why I included the condition "and are able to do so safely."
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But category A is a "normal" speed for a 182. The category is based on 1.3*Vs0 (or Vref if available) at max gross, which is less than 90 knots for a 182 in all configurations.
 
aterpster said:
No, you cannot select a lower category, only a higher category.
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I thought the category was determined by the speed being flown during the circling maneuver. If not, what speed is used to make the determination?
 
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