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Author Topic: ILS / LOC Approaches  (Read 25966 times)
KSYR-pjr
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« Reply #15 on: April 01, 2008, 04:02:36 PM »

From a pilot's standpoint, it's difficult to know how far out a particular localizer/GS is flight checked to.  But most localizer courses with GS are good for at least a dozen miles, many even more than that.  Wouldn't be able to make a string of pearls on final if everyone was turning on "at or very near the FAF."

I knew after rereading my post that someone would misinterpret it.  I was referring to glideslope intercept, not localizer intercept.  I said nothing about being turned onto the approach right at the marker, but I certainly will admit my wording was nebulous.  A better wording would have been: Controllers are descending aircraft below the glideslope well before the FAF so by the time they reach the FAF they intercept.  Better?
« Last Edit: April 01, 2008, 04:04:29 PM by KSYR-pjr » Logged

Regards, Peter
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« Reply #16 on: April 01, 2008, 04:13:29 PM »

Fair enough with the wording,

However, if you look at my example at DEN, you'll see the FAF is at DYMON, a mere 6.8 DME south (closer to 5 miles to the landing threshold really).  If one is shooting a triple simo app though, those planes are going to be dead on the needles, both loc and GS, by the time they hit CRUPP, and probably before that.

Aircraft will be up at right about 11k as well when they start their let down on the glide (gotta maintain vertical sep with the parallel runway landers until everyone is established on the Loc/GS for their respective runway).  Been to the TRACON many a time, watched it happen with mine own two eyes grin

Just sayin... the ATC situation is a very fluid one, and glide slopes can go out there a long ways as well with their paired localizer.

~Nate
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Greg01
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« Reply #17 on: April 01, 2008, 04:34:54 PM »

Jason has the jist of what I was trying to find. Unfortunately, I'm having a hard time trying to relocate my source. If any of the controllers on here could give an explanation, it would be greatly appreciated.

However, getting back to the main point: it doesn't matter where you join the GS, just that the charted GS intercept on an ILS approach is the FAF.

Thanks,
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Jason
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« Reply #18 on: April 01, 2008, 04:46:15 PM »

Jason has the jist of what I was trying to find. Unfortunately, I'm having a hard time trying to relocate my source. If any of the controllers on here could give an explanation, it would be greatly appreciated.

However, getting back to the main point: it doesn't matter where you join the GS, just that the charted GS intercept on an ILS approach is the FAF.

Thanks,


I had a tough time finding sources as well, Greg.  I couldn't find anything in the TERPS manual, just a guess off the top of my head.

I personally think of the glideslope intercept as shown by the lightning bolt symbol as the last possible opportunity to become established on the approach (both laterally and vertically) since ATC can clear you for the approach further out on many procedures.  If you don't intercept the glideslope by that point, you should really go missed and try it again (though there are some exceptions, wake turbulence is a good example).  If you're not properly established on the approach (which includes heading deviations of less than 2º inside the FAF) by the FAF, it's a good idea to go missed.  No sense in trying to salvage what you aren't already ahead of.  Of course, varying winds aloft make this difficult, but usually they will cooperate to allow a solid WCA to be maintained on the FAC prior to the FAF.
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tyketto
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« Reply #19 on: April 01, 2008, 04:51:49 PM »

And I think Nate has it nailed, especially with it being very fluid.

In the case of ILS 25L at LAX, the CIVET5 and RIIVR1 are profiled descents that bring you down to the IAF for the approach at FUELR, so you'll still be on the STAR until being given 'after FUELR, cleared ILS runway 25L approach. So while on the profiled descent of the STAR, you'll already be on the LOC for the ILS approach. you'd stay on the STAR until you pass FUELR, and after that you should have both the LOC and GS for your descent down. It just may be something fluid that is done that it's hard to pinpoint where one ends and the other begins, but the GS is definitely available further out than 10nm.

This was one of the biggest FAQs that was brought up when the old SocalTracon.com forum was up and ran by a controller at SCT.

EDIT: Unless they follow the chart down until HUNDA, which could be possible...

BL.
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KSYR-pjr
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« Reply #20 on: April 01, 2008, 05:02:24 PM »

However, if you look at my example at DEN, you'll see the FAF is at DYMON, a mere 6.8 DME south (closer to 5 miles to the landing threshold really).  If one is shooting a triple simo app though, those planes are going to be dead on the needles, both loc and GS, by the time they hit CRUPP, and probably before that.

Ok, just looked.  Just out of curiosity, are you typing from a controller's perspective or a big iron pilot's perspective?  I am questioning the idea that in this example pilots are capturing the glideslope that far out but I am not saying it's not possible - just curious:  Notice that the minimum altitude at CRUPP and others have a note that reads "Or as assigned by ATC" which seems to imply that assigned altitude could be lower.  Note also that the glideslope intercept on the chart also has a note indicating that ATC could assign lower.   

Thus, without knowing what the normal ATC practice is there (does ATC routinely descend aircraft to the lower intercept altitude or keep them up at 11,000 at CRUPP before clearing for the ILS approach?) I am not yet convinced that aircraft are intercepting the GS that far back.

Of course, if you are a United 777 pilot then you definitely know that you are intercepting that far back.  From the controller's scope? Eh, do you really?  Smiley Smiley

BTW, I am only a Bonanza pilot but I do fly IFR at least twice to three times every week in the Northeast US for business and Angel Flight.  Been doing that since 2004.  The biggest airports I have been to are BWI and Boston and I do these once every few months.  I almost went to JFK once but was fortunately talked out of it.  Hey, let's face it:  There really is no need for us little ones to clog up the movement at those monster class B airports with so many suitable satellite airports.  I have been to Denver in the Bonanza twice, though, to visit my brother there.  Landed one year at Platte Valley and the next at Erie Muni. 

edit: removed incomplete thought.
« Last Edit: April 01, 2008, 05:04:46 PM by KSYR-pjr » Logged

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KSYR-pjr
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« Reply #21 on: April 01, 2008, 06:54:59 PM »

And I think Nate has it nailed, especially with it being very fluid.

What does it mean to be fluid?   I seek some clarification on how that word applies in this case, since my understanding of the word is "always changing."
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« Reply #22 on: April 01, 2008, 07:18:57 PM »

Peter,

Give me time to dig up the appropriate references, I will get back to you later tonight.

~Nate
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tyketto
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« Reply #23 on: April 01, 2008, 07:21:29 PM »

And I think Nate has it nailed, especially with it being very fluid.

What does it mean to be fluid?   I seek some clarification on how that word applies in this case, since my understanding of the word is "always changing."


I believe what he was alluding to was that if the GS intercept is indeed only 10nm out, you're pretty much in no-man's land with the ILS approach, and are only following the descent as indicated on the chart until you have the GS. So if it is available further out, you're not just going from STAR - descent-per-chart - GS intercept, where it's choppy. the GS may be available further out than just 10nm to where it's a fluid even progression from end-of-STAR to GS.

BL.
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Greg01
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« Reply #24 on: April 01, 2008, 08:46:47 PM »

Tyketto, forget the STAR. Just take the STAR out of the picture completely. Let's say ATC has you direct FUELR and tells you to "Maintain 7000 until established on a published segment of the approach, cleared ILS 25L approach." After passing FUELR, just follow the minimum altitudes until you reach the GS intercept and your golden.

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KSYR-pjr
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« Reply #25 on: April 01, 2008, 09:43:36 PM »

I believe what he was alluding to was that if the GS intercept is indeed only 10nm out, you're pretty much in no-man's land with the ILS approach, and are only following the descent as indicated on the chart until you have the GS.

No man's land?  Hmmmm... not really.   The approach procedure contains very specific information about heading and altitude.

Once cleared for an ILS approach (regardless of where cleared), a pilot is authorized to descend to the minimum altitude for that segment of the approach, that is unless given a crossing restriction.  Hardly a no-man's land, which suggests a chaotic, free-for-all.  Smiley

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tyketto
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« Reply #26 on: April 02, 2008, 01:32:36 PM »

I believe what he was alluding to was that if the GS intercept is indeed only 10nm out, you're pretty much in no-man's land with the ILS approach, and are only following the descent as indicated on the chart until you have the GS.

No man's land?  Hmmmm... not really.   The approach procedure contains very specific information about heading and altitude.

Once cleared for an ILS approach (regardless of where cleared), a pilot is authorized to descend to the minimum altitude for that segment of the approach, that is unless given a crossing restriction.  Hardly a no-man's land, which suggests a chaotic, free-for-all.  Smiley



you're right. I was meaning that as a figure of speech. There is the approach segments as depicted on the chart. But what I was getting at is that if the GS is available further out than the 10nm intercept, you wouldn't only have the individual segments of the approach to use, but also the GS as well. Either one should suffice.

And I also  need to correct myself. As far as west ops are concerned and ILS approaches, PTAC would be given to TEC routes from the west (say, PSP, ONT, RAL, etc.). They'll be kept out of the CIVET/RIIVR stream until closer to the field (LAHAB) then either given the visual or ILS approach.

BL.
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KSYR-pjr
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« Reply #27 on: April 02, 2008, 02:25:25 PM »

But what I was getting at is that if the GS is available further out than the 10nm intercept, you wouldn't only have the individual segments of the approach to use, but also the GS as well. Either one should suffice.

I was hoping that one of the airline pilot's who frequent here would have jumped in by now to offer their practice regarding capturing the GS so far back (meaning, is it acceptable or is there some type of airline operating policy that sets a limit as to how far back to do so). 

In the meantime, I can only offer my perspective as a little blip:  If I were not already descended to an intercept altitude that permitted an intercept within about 10 miles or so and I was not given any type of interim descent limit, I would "dive and drive" to an altitude permitted by the approach when cleared for the approach, rather than capture that far back.

Or, now that my aircraft is equipped with WAAS I would come down the GPS glideslope on an LPV approach, since that signal can be used way out.  Smiley  Smiley
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« Reply #28 on: April 02, 2008, 09:35:17 PM »


Technically, the lightning bolt in the profile view is the glideslope intercept altitude (GSIA).  It's the altitude you have to be at near where you're supposed to be at where you're guaranteed to capture the real glideslope.  Above the glideslope, there are false glideslopes at angles of roughly 6 degrees (upside down), 9 degrees (rightside up), 12 degrees (upside down), etc...

Before you get to the GSIA point, you're not supposed to use the glideslope for vertical guidance.  Most of us in bugsmashers without VNAV will do the "dive and drive" to each segment altitude.  Airliners with FMS will have the FMS calculate a smooth descent profile that keeps them above the min segment altitudes.

GSIA usually occurs somewhere near the Non Precision FAF.

Oh, and ATC is not supposed to vector you to the FAC above the GS, (due to the false glideslopes up there), and on a vectors to final, the intercept point has to be outside the approach gate, which is either 5 miles away from the airport, or 1 mile outside the FAF/GSIA, whichever is farther.

--Carlos V.

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« Reply #29 on: April 02, 2008, 09:37:50 PM »


Or, now that my aircraft is equipped with WAAS I would come down the GPS glideslope on an LPV approach, since that signal can be used way out.  Smiley  Smiley

True, but according to the WAAS TSO, the box won't annunciate LPV/LNAV/LNAV-VNAV/ LNAV+V and generate the synthetic glideslope until you're within 3 miles of the FAF and going in the right direction.

--Carlos V.
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