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Author Topic: ILS / LOC Approaches  (Read 36352 times)
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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« 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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« Reply #30 on: April 02, 2008, 09:46:35 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.


Drat, I need to go look for my references, but another board had a similar discussion, and that could get you in trouble.  I need to look myself since it involves math it might take a while. Some approaches had the GS dip below the intermediate segment min altitudes.  I think LAX was one of them.  One should always not fly the GS until you capture it at the GSIA.

Edit to add: Yup, it was LAX.  Both 25s ILSes put you 400ish feet too low at at least one fix.  25L at 3 degrees puts you at 4590 feet at GAATE (which is 15.2 miles out), which has a min altitude of 5000.  25R puts you at 4560 at FALLT (15.3 miles) who's min is 5000.

--Carlos V.
« Last Edit: April 02, 2008, 09:53:45 PM by Unbeliever » Logged
tyketto
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« Reply #31 on: April 03, 2008, 01:18:46 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.


Drat, I need to go look for my references, but another board had a similar discussion, and that could get you in trouble.  I need to look myself since it involves math it might take a while. Some approaches had the GS dip below the intermediate segment min altitudes.  I think LAX was one of them.  One should always not fly the GS until you capture it at the GSIA.

Edit to add: Yup, it was LAX.  Both 25s ILSes put you 400ish feet too low at at least one fix.  25L at 3 degrees puts you at 4590 feet at GAATE (which is 15.2 miles out), which has a min altitude of 5000.  25R puts you at 4560 at FALLT (15.3 miles) who's min is 5000.

--Carlos V.

Could you compare that to the 24s? I'm wondering if it is because those coming in from the south or the west via the LEENA2 arrival going to the 24s may be vectored behind and above the 25 stream to keep the separation there through the gates.

This is good stuff all around! Smiley

BL.
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keith
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« Reply #32 on: April 03, 2008, 02:47:53 PM »

There are folks here with much more flying experience than me, but as an instrument student, I've been taught (and have read) that the glideslope should be ignored until reaching the lightning bolt. Prior to that, you should use the minimum altitude published for each approach segment.

The fact that the glideslope might be received prior to the GSIA is irrelevant, and should be ignored (due to the false slopes that might exist, or due to published intermediate stepdown fixes along the way).

Here's a question I've had for a long time, and this seems like the best place to ask it...

Listening to the KSNA feed, the PTACs for the ILS 19R are usually done with reference to LEMON.  "4 from LEMON, fly hdg 160, maintain [MVA] until established, cleared ILS RWY 19R approach."  Given that the FAF for a precision approach IS the GS intercept point (SNAKE, in this case), and that the aircraft should join the localizer prior to the gate (which is outside SNAKE), why are they referencing LEMON instead of SNAKE?

The chart's here for anyone who wants to review it: http://204.108.4.16/d-tpp/0803/00377I19R.PDF

So, that's the question, why vector with reference to LEMON?

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Jason
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« Reply #33 on: April 03, 2008, 04:01:01 PM »

So, that's the question, why vector with reference to LEMON?

Many controllers reference the outer marker on the procedure (if one exists) in the PTAC, but it varies by facility.  I don't exactly know why, but I've heard this done all over the country in many different places.  If you ever listen to JFK Final, you can hear them doing it often as well.  I would imagine its for situational awareness since the outer marker and co-located intersection are more easily noted on the chart than another random fix on the approach, but you do bring up a good point that the lightning bolt is very close to/in reference of SNAKE intersection.

Also note that if ATC directs a lower-than-published glideslope/path intercept altitude, the resultant actual point of the glideslope/path intercept at the altitude authorized to maintain until established becomes the precision FAF.
« Last Edit: April 03, 2008, 04:07:49 PM by Jason » Logged
mk
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« Reply #34 on: April 03, 2008, 04:40:25 PM »

i'm gonna paraphrase the 7110.65 the ATC manual b/c i'm out of town for a few days but the FAA's 7110.65 definition of the FAF on an ILS is "the point the aircraft intercepts the glideslope".  most of the time the controller will give the lowest altitude restriction he can depending on his minimum vectoring altitude in the area.  He can clear you at the IAF if he wants as long as you are at or below the GS crossing altitude at that point.  at bwi, we clear anywhere from 4000' to 2000' on rwy 33L, but you'll notice that the altitude at RUETT is 1500'...we can only go to 2000' due to the MVA.  So, right there adds another mile out from the runway, plus a mile for the gate, plus 2 more miles to meet the 7110.65 requirements and you're now 8 miles from the runway...now if i clear you at 3000' for the ILS 33L, add 3.3 more miles to that...

as far as the question of whether or not a localizer or glideslope goes out  25 miles or whatever, just look at the chart...the IAF is most likely as far as the TERPS folks feels the GS is reliable. 
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« Reply #35 on: April 03, 2008, 04:52:45 PM »

Jason,

I didn't ask the question very clearly. A distance from the marker is indeed very good for situational awareness. That's not my concern.  The issue is having the plane join the localizer inside the bolt...however, if the controller is allowed to throw away the lightning bolt, then I guess it works out Smiley
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« Reply #36 on: April 03, 2008, 05:19:01 PM »

The full published procedure is for approaches without RADAR assistance, it keeps you at a safe altitude prior to intercept.  (I should say Terminal radar assistance.)

When radar vectors are provided, we TRACONs can vector to intercept below the GS but not below the MVA.  If you get a close turn on (say at the gate) you will NOT have to chase the descent while achieving course guidance.  We (ATC) aren't ignoring the published procedure, it doesn't apply when ATC is involved (kind of an ATC shortcut).  But then you must be working with a TRACON.

For example, Enroute controllers who assume approach control airspace for part-time facilities normally do not have radar coverage to provided detail approach guidance below most altitudes, in my airspace sometimes traffic is not visible below 5000' for a sea level airport.  Their radar doesn't update as quickly, they cannot use mode C for separation etc, so they usually vector to an IAF or transition, Terminal controllers will vector (pending on the weather) closer and lower.
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« Reply #37 on: April 03, 2008, 05:34:58 PM »

  most of the time the controller will give the lowest altitude restriction he can depending on his minimum vectoring altitude in the area.  He can clear you at the IAF if he wants as long as you are at or below the GS crossing altitude at that point. 

Practically, as a pilot, if I'm getting vectors, and I become established and receive a "cleared for the approach" I will fly the lowest of 1) Assigned altitude or 2) min segment altitude.  I.e. assigned 3000, you vector me onto a segment that says 4000, the next segment is 2000, I will fly 3000 when cleared for the approach until I hit the 2000 segment.

Quote
as far as the question of whether or not a localizer or glideslope goes out  25 miles or whatever, just look at the chart...the IAF is most likely as far as the TERPS folks feels the GS is reliable. 

IAF? You mean precision FAF right?  The IAF can be anywhere and be based on navaids other than the localizer.

--Carlos V.
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« Reply #38 on: April 03, 2008, 05:41:24 PM »


Could you compare that to the 24s?


Both Glideslopes appear to be above all previous min segment altitudes.  They're above JULLI and MERCE by 300 feet.

FYI: a 3% glideslope is 318 feet per nautical mile.  The rule of thumb for simplified cockpit calculations is 300 feet/nm.

--Carlos V.
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Jason
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« Reply #39 on: April 03, 2008, 05:48:24 PM »

Jason,

I didn't ask the question very clearly. A distance from the marker is indeed very good for situational awareness. That's not my concern.  The issue is having the plane join the localizer inside the bolt...however, if the controller is allowed to throw away the lightning bolt, then I guess it works out Smiley

I suppose I didn't answer it too clearly either.  As Natasha alluded to, the charted lightning bolt in practicality, is to be used if you've been cleared for the full approach (no VTF) outside of radar coverage.  Since ATC can change the intercept altitude to whatever they want (though it must be below the GS and above the MVA) the resultant point of the altitude assigned and the glideslope/glidepath intercept becomes the new precision FAF, and thus, the charted lightning bolt does not apply.
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« Reply #40 on: April 03, 2008, 06:03:00 PM »

  As Natasha alluded to, the charted lightning bolt in practicality, is to be used if you've been cleared for the full approach (no VTF) outside of radar coverage.

Incorrect.  Even with VTF, the pilot should descend to the GSIA before following the glideslope.

For example, CNO ILS 26R that I got tons and tons of time in training.  SoCal usually gives us vectors to final at 3000 outside LINDN.  By coincidence, the GS intersects at LINDN right at 3000, and when I'm flying the needle does come down to center at that point.  HOWEVER, once I hit LINDN, I don't follow the GS down, but do a non-precision descent to 2100, and begin following the GS once it re-centers at DEWYE.  TERPS chose that point for a reason, and we as pilots don't know it.  The GS is not guaranteed out beyond the normal GSIA point so we have to fly it as charted.

Of course, if I'm below the GSIA when I am established on the FAC I'll start down at whatever point I intercept, but in practicality, I should never receive that since ATC is supposed to vector us at least a mile farther out from that point.  I have a copy of .65 at home that I'll look up for reference.

--Carlos V.
« Last Edit: April 03, 2008, 06:04:33 PM by Unbeliever » Logged
Jason
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« Reply #41 on: April 03, 2008, 07:12:01 PM »

Incorrect.  Even with VTF, the pilot should descend to the GSIA before following the glideslope.

There is nothing that requires a pilot to descend to the GSIA before using the glideslope signal.  If ATC clears you for the approach 10 or 15 miles out, maintaining 1,000 feet above the GSIA (which is still below the glideslope), you have two options.  You can either maintain 3,000 feet until you intercept the glideslope, or you could descend down to the GSIA and intercept down there.  The only thing you can't do is descend below the minimum altitude for the prescribed route segment on the approach.  If you use Jepps, you'll notice the second method is depicted much more clearly than on the NACO charts (shown as stepdowns), but most commercial pilots (airline, corporate, fractional, etc) opt to remain at the altitude assigned by ATC until GS intercept since it provides a much smoother descent.

As long as ATC assigns an altitude below the glideslope and above the GSIA, you're cleared to remain at that altitude until you capture the glideslope.

Quote from: 7110.65S §5-9-1
b. For a precision approach, at an altitude not
above the glideslope/glidepath or below the
minimum glideslope intercept altitude
specified on
the approach procedure chart.
« Last Edit: April 03, 2008, 07:15:00 PM by Jason » Logged
mk
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« Reply #42 on: April 04, 2008, 11:26:51 AM »

no, carlos, i meant the IAF...it's my understanding along with numerous controllers i work with that the IAF is placed at it's location on each approach by the TERPS folks basically saying that this fix is as far out as the GS can be 100% trusted.
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« Reply #43 on: April 04, 2008, 05:19:45 PM »

no, carlos, i meant the IAF...it's my understanding along with numerous controllers i work with that the IAF is placed at it's location on each approach by the TERPS folks basically saying that this fix is as far out as the GS can be 100% trusted.

Drat, the on-line version of TERPS is missing so many chapters I have to go to anecdotes instead of refrences.

To that point I present RAL ILS 9 as a counter-example.  SLI is an IAF and is 30 miles away, way off angle, roughly 35-40 degrees, and on the other side of a mountain (Pleasant's peak).  I doubt you can get either the localizer OR the glideslope from over SLI.  What SLI does have is a route segment that tells you how to get to the LOC.  From SLI is not a feeder route, it is a full blown IAF and intermediate segment of the approach.

And I can't provide a reference to intercepting at GSIA since both TERPS and whole chunks of Part 97 are not on line.  But to nitpick, 7110.65 5-9-1 is an instruction to controllers on where to put pilots on a VTF, not what the pilot is cleared to do.

The header to 5-9-1

Except as provided in para 7−4−2, Vectors for Visual
Approach, vector arriving aircraft to intercept the
final approach course:


And thanks, 5-9-1 (b) provided a reference to my statement that ATC isn't supposed to put you below GSIA either.

--Carlos V.
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Jason
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« Reply #44 on: April 04, 2008, 06:01:10 PM »

Drat, the on-line version of TERPS is missing so many chapters I have to go to anecdotes instead of refrences.

To that point I present RAL ILS 9 as a counter-example.  SLI is an IAF and is 30 miles away, way off angle, roughly 35-40 degrees, and on the other side of a mountain (Pleasant's peak).  I doubt you can get either the localizer OR the glideslope from over SLI.  What SLI does have is a route segment that tells you how to get to the LOC.  From SLI is not a feeder route, it is a full blown IAF and intermediate segment of the approach.

And I can't provide a reference to intercepting at GSIA since both TERPS and whole chunks of Part 97 are not on line.  But to nitpick, 7110.65 5-9-1 is an instruction to controllers on where to put pilots on a VTF, not what the pilot is cleared to do.

The header to 5-9-1

Except as provided in para 7−4−2, Vectors for Visual
Approach, vector arriving aircraft to intercept the
final approach course:


And thanks, 5-9-1 (b) provided a reference to my statement that ATC isn't supposed to put you below GSIA either.

--Carlos V.

There is no requirement of any sort in the federal aviation regulations that a pilot must descend to a minimum altitude on an instrument approach unless a mandatory altitude is published.  Of course, what I posted above also applies as well (a pilot may not descend below the minimum altitude for the prescribed route segment on the approach).  Rod Mochado also gave the same answer to a pilot whose friend's instrument student failed an instrument checkride for not descending to the GSIA on an ILS approach.

Since you brought it up, JO 7110.65S §5-9-1 absolutely does concern what altitude ATC may assign an aircraft when vectoring ato intercept the final approach course.  As I referenced in my last post, sub-para (b) of this section makes that distinction.  ATC may not vector an aircraft to intercept the FAC below the GSIA, or above the glideslope/glidepath at the point of interception.  If the altitude assigned meets this criteria, then the pilot may fly that altitude to capture the glideslope.
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« Reply #45 on: April 04, 2008, 06:59:30 PM »


Since you brought it up, JO 7110.65S §5-9-1 absolutely does concern what altitude ATC may assign an aircraft when vectoring ato intercept the final approach course

By the way, we've been violently agreeing on .65 and ATC's requirements. I was just nit-picking about using .65 to justify Pilot behavior.  I'm just spending my time looking through Government sources on what the Pilot should do.  This weekend I'm probably hitting the ACs.

In praticality, unless you're a good math whiz in the cockpit while flying, and know the surrounding terrain/airspace.  It's best to follow the profile as charted.  The aforementioned LAX ILS 25s have produced many violations for pilots following the GS too far out.  Especially on hot days where true altitude is higher than indicated altitude.  The GS doesn't move, but Ontario's traffic was closer to the GS as their true altitude was higher on a hot day and caused separation issues. (which was the LAX traffic's fault, not the Ontario traffic's fault)

I'm of the opinion that if I make a statement, I've got to back it up.... which is why I'm still looking. *grin*


--Carlos V.
« Last Edit: April 04, 2008, 07:02:19 PM by Unbeliever » Logged
mk
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« Reply #46 on: April 06, 2008, 10:51:00 PM »

unbeliever,

The IAF doesn't need to be located on the LOC.  we have one at BWI ILS 10...it's offset at least 20 degs.  still, you will get the clearence to cross DATED at or above 2500', cleared ils 10 app.  it's the pilot's perogative to track inbound to COLUM and join the LOC.  I don't see how this relates to the original topic of FAFs...because regardless of where the IAF is or where you join an approach, the FAF on an ILS is the point at where the aircraft intercepts the glideslope.   on the ILS10 at BWI if you were cleared over DATED, you would intercept the GS at COLUM at 2500'.  if i vector you to final you will get a descent to 2000' and then the FAF would be between COLUM and JEANS. 
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KSYR-pjr
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« Reply #47 on: April 07, 2008, 11:27:55 AM »

I'm of the opinion that if I make a statement, I've got to back it up.... which is why I'm still looking. *grin*

Carlos, any more information on this?  I am curious what official source states that one must descend before intercepting the GSIA at the published point, too, since I don't recall ever running across this throughout training or in the real IFR world. 

As stated, I do this now but I don't recall a published regulation/Instrument manual requirement to do so.
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« Reply #48 on: April 07, 2008, 12:05:59 PM »

Haven't found it amongst government publications, just amongst training manuals.  Though I haven't spent as much time on it as I wanted.

I'm thinking of putting the question on AOPA's board.  I'm sure Capt. Ron would have an opinion and a source. *grin*

--Carlos V.
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« Reply #49 on: April 07, 2008, 01:31:43 PM »

Still looking for something stronger.  91.175 (a) says you must use a SIAP, and the chart itself is a graphical description of the SIAP, which is part of Part 97, itself regulatory.  The chart says "This is where you intercept the glideslope"

Other than common sense, I'm still looking for a stronger statement of "don't fly the GS until the charted  point."

--Carlos V.

ETA: Hmmm. a blow to me.  AC120-29A uses the phrase "published minimum GSIA" which suggests by inference contrary to my position.  Still looking.
« Last Edit: April 07, 2008, 01:42:38 PM by Unbeliever » Logged
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