Note that the 60-to-1 isn't a "rule" but an approximation which works given how sloppy people navigate. It's really the 57.2958-to-1 rule.
Glideslope Intercept
- Thread starter drjcustis
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I simply do not read it anywhere near with the tightly focused-on-the-individual-tree glasses you do.
Actually not even one of those "other references" support what you say unless you choose to spin it based on your preconceived slant. Let's take a look.
- "Awareness of this altitude when intercepting the glideslope can ensure the flight crew that a “false glideslope” or other erroneous indication is not inadvertently followed." Of course that's true. No one has argued that one should blindly follow the GS through the PFAF without using the altitude crosscheck published on the chart. Plus, we've already established that the TERPS requirements from IF to FAF preclude any chance of a false glideslope. And of course, reading the guidances as a whole, one realizes immediately that they are not with a false glideslope; they are concerned busting altitude following the real one.
- Yep, "The final approach segment for an approach with vertical guidance or a precision approach begins where the glideslope/glidepath intercepts the minimum glideslope/ glidepath intercept altitude." Definitely. Again no one has said anything to remotely suggest a different definition. Whether you reach it as you cross through on glideslope or while motoring along a lower altitude for a few miles in advance, you have not reached the final approach segment until you reach the PFAF .
- "If ATC authorizes a lower intercept altitude..." Of course, if ATC says, "maintain XXX until established..." while vectoring us to the FAC, that's what we do. But what that has to do with when that instruction is not received is beyond me.
BTW, to others, especially CFIIs. I have heard of other DPEs with the same viewpoint - they prefer dive and dive to early stabilization, although AFAIK, none of them specify the supposedly "proper" descent rate or how far from the PFAF you "must" be at the intercept altitude. But its a fair bet it cannot be at 450 FPM at 90 KTS since the DPE might think you are following the glideslope!
You might consider teaching this is the same way as some other tasks: "here's what the DPE wants to see, but here's how to do it in the real world."
Ryan F.
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I can't find any middle ground here - it almost seems you are reading/interpreting something totally different than I am.
I am not aware of any interpretations which support anything other than a literal reading of everything which has been presented. I am simply at a loss as to how you can arrive at any different conclusion.
Real world application, that's a different matter and outside the realm of the discussion. The language is what the language is, so that's that.
You are, of course, free to believe and teach what you wish.
Best of luck,
Ryan F.
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The issue we're having here, Mark, is that you're simply not reading the guidance word for word.
Intercepting the glideslope. That means arriving at glideslope intercept at the published (or assigned) glideslope intercept altitude.
The language is quite specific. All references indicate this manner of intercept. They do not suggest arriving at the PFAF already on the glideslope. Every single reference refers to intercepting the glideslope. If you coordinate the note in the AIM with every other piece of guidance presented, it is quite clear that the intention is for the user to intercept the glideslope at the published (or assigned) glideslope intercept altitude.
Is it really possible you can read this any other way? How? I'm genuinely at a loss trying to understand how you might support your position on this.
Intercepting the glideslope. That means arriving at glideslope intercept at the published (or assigned) glideslope intercept altitude.
The language is quite specific. All references indicate this manner of intercept. They do not suggest arriving at the PFAF already on the glideslope. Every single reference refers to intercepting the glideslope. If you coordinate the note in the AIM with every other piece of guidance presented, it is quite clear that the intention is for the user to intercept the glideslope at the published (or assigned) glideslope intercept altitude.
Is it really possible you can read this any other way? How? I'm genuinely at a loss trying to understand how you might support your position on this.
Pressures changes should have no bearing on the altitude at which you intercept the glideslope as we correct for pressure changes by using the pressure setting for the field.
As to temperature changes, it is true that temperature can cause significant error in the intercept point of the glideslope. The typical altimeter however does show some error relative to temperature and is permitted up to +/-75ft of error primarily for this reason. The actual error of the altimeter in varying temperatures varies from altimeter to altimeter and is not a precise variation (that is in most instances, applying the correction value indicated for the temperature to my indicated altitude on the ground will not yield for me the field elevation but it generally gets pretty close) so for our purposes right now we'll assume up to 50ft of this error is temperature related (50ft higher in warmer weather and 50ft lower in colder weather).
Legally speaking the FAA requires us to correct for cold weather once we are below 0C (and 15C from standard) by increasing the published altitudes due to the fact your true altitude is significantly lower than indicated. The end result is that the indicated altitude at PFAF is much higher than normal but true altitude remains the same.
Going the other direction the FAA does not require nor provide temperature correction information for warm weather however, it does require us to cross the FAF at the appropriate indicated altitude (even though we are higher than indicated in warm weather). We can use the temperature correction formulas to find the correction is 50ft or less up to a temperature of about 25C so at 25C our indicated altitude should be about accurate considering altimeter error. Above 25C, you'd have to get to 30C to have a further 25 ft of error and 35C to get to 50ft error. These errors are not insignificant but they are within usual tolerances for an approach, especially for altitudes prior to beginning the final approach segment. Its not until you reach temperatures in the 40+C range that your errors become large enough to exceed the ACS standard of +/-100ft for altitudes restrictions on a precision approach prior to the final approach segment.
Oh and all those correction values are for 1700ft above an airport that is at 700ft. The temperature corrections get smaller as the altitude above the airport is reduced.
So does temperature factor in? Yes it does but the amount of error you will see at that altitude and temperatures up to 45C is going to be a maximum of 150ft and likely at least 50ft less due to the effects of temperature on altimeter error. This amount of error is likely to be a 1 or 2 dot deflection of the glideslope indicator.
I'm not saying you should completely disregard the effects of temperature or deviate below the appropriate indicated altitude but in a majority of instances temperature is likely having a much smaller impact on your ILS than you would think except in extreme colds (for which there is a published procedure to increase minimums)
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Easily. I dont read it word for word applying whatever a definition of a given word I deem appropriate. I read it just as I would read anything else looking at the entire text for contextual clues about which definition to apply and how. Especially when interpreting the AIM which is written in descriptive paragraph form.
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aterpster
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aterpster
In the absence of stepdown fixes between the IF and the PFAF, as in the example IAP, what possible airspace violations or other pilot deviations do you foresee it I elected to remain at 4,000 until intercepting the GS? By maintaining 4,000 until GS interception my defense would be that I am conducting best safety practices by starting a constant descent angle in the intermediate segment where there may be obstacles as little as 500 feet below the 2,400 intermediate segment alitude.
luvflyin
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I haven't been following the thread in detail for awhile but I think I get the gist of the arguments going on now. What exactly do you mean by "glideslope intercept" in the sentence "That means arriving at glideslope intercept at the published (or assigned) glideslope intercept altitude."? If it's the location indicated by the 'lightning bolt' I can think of no easier way to do that then by being already on the Glideslope. If you are saying you just flat cannot 'intercept' the Glideslope until then, you are wrong. You can always intercept the Glidesope before then unless that is the altitude you were assigned as an 'at' altitude if having been vectored to final. Sometimes not to soon before then if there is a fix before there that has an altitude you must comply with that the Glideslope will take you below due to hot temperature. If that happens you will have to be above the Glideslope for a bit and then get back down after passing that fix. But to say you must then go back down through the Glideslope to the Minimum Glideslope intercept altitude and then intercept it again from below is ludicrous. Maybe i got the gist wrong.
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Ryan F.
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Practically speaking, I agree with you.
I hope it's been clear that I'm not advocating any particular method or technique here -- just discussing the AIM and InFO notes as it pertains to Precision Instrument Approach Procedures. The AIM's guidance is clear, even if it would seem to be superfluous in the case of the example being discussed.
One could also argue that from a "best practices" standpoint, a standardized methodology could reduce the number of deviations on the TEB ILS runway 6 approach, for example (mandatory 1500' altitude at DANDY prior to intercepting the glideslope at 1300'.) Pilots who become accustomed to intercepting the glideslope at a location other than the published glideslope intercept altitude may be at greater risk of a pilot deviation on such approaches.
However, just to be clear: the bottom line from a regulatory and airman certification standpoint is, so long as the airman remains above/at any published minimum/mandatory altitudes on the approach, he or she may feel free to use any of the techniques discussed in this thread. The AIM's guidance is contrary to those techniques, but they're available.
I think I'm just about "talked out" on this subject now. I don't think I can type "published glideslope intercept altitude" one more time.
dtuuri
Final Approach
How's that?
@300'/NM times 6NM you'd lose 1800' (1884.9549' for flyingron) and cross 200' high (115.046' high for flyingron). Or wouldn't you?EDIT: Never mind. I forgot you aren't on the GS @ IRRON. The GS intercept there would be 10287' (not for flyingron—he can figr it oot himself
).
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My math skills suck, but I started with the PFAF at 6000 and worked backward from there. It's 8.9 nm from the PFAF back to TOOME. 8.9 X 318 is 2,830. Add that to the 6000 and I get the GS crossing TOOME at 8,830.How's that?
dtuuri
Final Approach
I apologize for not seeing my mistake before you replied.
You did it better than me, working back from PFAF. I added all the distances to the threshold from IRRON. This pin-dance of a thread fogged my mind. My 2¢ is: If in doubt whether the GS indication is reliable, fly the minimum segment altitude instead. Otherwise, fly the GS but not below the minimum altitude published for the segment, i.e., monitor the progress and call out the fixes stating the new minimum as you go. Over and out.
100% agree.I apologize for not seeing my mistake before you replied.
Funny thing about this thread. One might not think so but 90% of the time I "drive down" to the minimums and don't "stabilize early." I think stabilize early is a better operational method, but I was originally taught drive down (as the way to ensure no false glideslope) and didn't even come across stabilize early until LPV where there is no false glideslope issue at all. The 10% where I do stabilize early requires a lot of extra thought to go against habit.
luvflyin
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More thoughts on the subject.
NOTE 2. of 5-4-5 b. Notes are informative, not directive. That Note also goes on to explain "...If the pilot chooses to track the glide slope prior to the glide slope interception altitude, they remain responsible for complying with published altitudes for any preceding stepdown fixes encountered during the subsequent descent..." They condone, so to speak, intercepting the Glideslope beyond that point. Provided of course that you don't follow it below a published minimum altitude. Now pilots should take AIM 1-1-9 d. into consideration before deciding how far out they may want to 'choose' to start following the Glideslope.
The Published Glideslope Intercept Altitude is rarely a hard altitude. You will find a few where that altitude is both underscored and overscored. If so, then yes, you must be at that altitude and not on the Glideslope until that point.
NOTE 2. of 5-4-5 b. Notes are informative, not directive. That Note also goes on to explain "...If the pilot chooses to track the glide slope prior to the glide slope interception altitude, they remain responsible for complying with published altitudes for any preceding stepdown fixes encountered during the subsequent descent..." They condone, so to speak, intercepting the Glideslope beyond that point. Provided of course that you don't follow it below a published minimum altitude. Now pilots should take AIM 1-1-9 d. into consideration before deciding how far out they may want to 'choose' to start following the Glideslope.
The Published Glideslope Intercept Altitude is rarely a hard altitude. You will find a few where that altitude is both underscored and overscored. If so, then yes, you must be at that altitude and not on the Glideslope until that point.
No fair. You read all the words.
Ryan F.
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It's not a directive, it's a recommendation. My issue all along is to ensure it's clear what the guidance says. You may intercept the glideslope wherever you like so long as you remain above/at minimum/mandatory altitudes. But the AIM makes it clear that the intention is for the user to intercept the glideslope at the published glideslope altitude. There's no way to pull that out of black and white and make it grey. (By the way, the "underscored and overscored" altitudes are called mandatory altitudes.)
And all sorts of things are found in "Notes..." Be careful trying to define what counts and what doesn't because notes "seem" unofficial to you. It's the AIM, so it's not "regulatory," yet there is a huge body of expanded information on instrument flying which is found within the various volumes. And a great deal of that is found within "notes."
Best of luck,
There are several definitions for the word intended but the hang up between you and I seems to be between the 2 definitions of the verb form:
1) plan that (something) function in a particular way.
"a series of questions intended as a checklist"
2) design or destine (someone or something) for a particular purpose or end.
"pigs intended for human consumption"
Contextually, the paragraph reads to me as using definition 2. The glide slope is designed for the purpose of providing vertical guidance, specifically only from the PFAF onward. The ILS is intended to be used by IFR pilots to help them find the runway; that doesn’t mean the ILS can’t be used by IFR pilots for other purposes (fix identification, location verification, etc) or by VFR pilots in the same manner.
On the other hand, you seem to prefer definition 1 which I can certainly see a conflict between #1 and #2 in the context of our conversation since we are talking about how to fly the glide slope but to me it doesn’t contextually fit with the surrounding text in the AIM. The glide slope is planned to function (be flown) in a particular way.
This confusion and mixing of the definition applies to other points too, not just the PFAF. The glideslope is intended to be flown all the way to MAP or landing but once I have and can maintain a visual of the runway environment, I am free to deviate from the glideslope as I see fit to facilitate a landing. This deviation may even be required on short runways where the glideslope touchdown point is too far down the runway for proper flare and ground roll such that it becomes necessary to go below glideslope to flare earlier and touchdown at or before the point where the glideslope meets the runway.
These may be subtle differences overall but it explains how something so “black and white” as you put it can be made grey.
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aterpster
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aterpster
The AIM is written by committee. Each section has its own "office of responsibility." There are historical instances of AIM passages deemed inadequate or misleading, with subsequent changes. You are hung up on language that was written to try to prevent altitude busts, such as happened at LAX, SEA, and ORD. The vast majority of the ILS and LPV approaches in the U.S. do not have intermediate segment step-down fixes. A competent pilot should always be aware of the specifics of a particular IAP before he leaves the en route environment. In the LAX case, the altitude busts occurred in the initial approach segment of four very complex ILS approaches (which have extended service volume on the four localizers from the east).
After the LAX busts kept happening:
1. FAA redesigned the step-downs to mitigate the issue.
2. The airlines issued a bulletin that advised crews to use Baro VNAV for descent from the east at LAX until the PFAF becomes the active waypoint.
LAX was my home base, and before RNAV or VNAV. We would always fly the GS from 10,000. But, we knew enough that the stepdown fixes were controlling prior to the GS intercept point (Jepp shows it differently than FAA charting). It was a rare approach where we had to ease above the GS to comply with the step-down fixes out in the KONT area (hot summer day).
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Ryan F.
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Thanks, aterpster.
I'm not hung up on anything. I'm quoting the AIM. Obviously some view it differently, despite the clear language contained within. I'm drawing a hard line on what the guidance means, not what users need to do out in the field. 'Nuff said on that. I'm not repeating the AIM's guidance again.
I agree that since the LAX approaches were redesigned, this became less of an issue. I view the ILS runway 6 into TEB as a similar "problem" approach despite the mandatory altitude at DANDY being quite obvious in the procedure. It's easy to say, "we'll just fly the glideslope" and forget the mandatory crossing altitude at DANDY. We are creatures of habit; we tend to revert to habit even when the procedure is clear. Another reason why the guidance still contains merit.
I've flown the LAX and TEB approaches more times than I can count in my career. When this was a hot topic 'round 2010-2011, I was seeing the LAX runway 25L appear in my sim profiles. I had one current type which let me fly the stepdowns with VNAV, and another single-pilot jet type which forced me to use vertical speed for the stepdowns. The training industry treated this as a real issue. It has faded away in recent years, but the guidance remains.
Thanks for an interesting discussion, despite everyone not seeing eye to eye.
I'm not hung up on anything. I'm quoting the AIM. Obviously some view it differently, despite the clear language contained within. I'm drawing a hard line on what the guidance means, not what users need to do out in the field. 'Nuff said on that. I'm not repeating the AIM's guidance again.
I agree that since the LAX approaches were redesigned, this became less of an issue. I view the ILS runway 6 into TEB as a similar "problem" approach despite the mandatory altitude at DANDY being quite obvious in the procedure. It's easy to say, "we'll just fly the glideslope" and forget the mandatory crossing altitude at DANDY. We are creatures of habit; we tend to revert to habit even when the procedure is clear. Another reason why the guidance still contains merit.
I've flown the LAX and TEB approaches more times than I can count in my career. When this was a hot topic 'round 2010-2011, I was seeing the LAX runway 25L appear in my sim profiles. I had one current type which let me fly the stepdowns with VNAV, and another single-pilot jet type which forced me to use vertical speed for the stepdowns. The training industry treated this as a real issue. It has faded away in recent years, but the guidance remains.
Thanks for an interesting discussion, despite everyone not seeing eye to eye.
aterpster
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aterpster
Lot of changes have been made to the AIM over the years 1992-present because of the input of pilot groups (AOPA, ALPA, NBAA, Allied Pilots, USAF) to the Aeronautical Charting Forum (slightly different name now). Some language was changed because it was wrong, some was changed because it was misleading or incomplete.
"Landmark" accidents have also resulted in both regulatory and AIM changes.
1. TWA/UAL Grand Canyon mid-air 1956.
2. UAL/F-100 mid-air over Las Vegas 1957.
3. TWA/UAL mid-air over Brooklyn, NY 1960.
4. TWA DC-9 Beechcraft mid-air near Columbus, OH 1967.
5. TWA 514 CFIT west of IAD, 1974.
6. AAL CFIT in Colombia, 1995.
"Landmark" accidents have also resulted in both regulatory and AIM changes.
1. TWA/UAL Grand Canyon mid-air 1956.
2. UAL/F-100 mid-air over Las Vegas 1957.
3. TWA/UAL mid-air over Brooklyn, NY 1960.
4. TWA DC-9 Beechcraft mid-air near Columbus, OH 1967.
5. TWA 514 CFIT west of IAD, 1974.
6. AAL CFIT in Colombia, 1995.
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