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Author Topic: ILS / LOC Approaches  (Read 24027 times)
Greg01
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« on: March 31, 2008, 04:42:05 PM »

Not to nit-pick, but the FAF on an ILS is the glideslope intercept. GS intercept is usually at or near the marker, but it isn't always.

Greg

[MOD] This thread was split from, and refers to "JetBlue wants to play games" [/MOD]
« Last Edit: April 01, 2008, 07:22:53 AM by Jason » Logged
tyketto
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« Reply #1 on: March 31, 2008, 08:33:42 PM »

Not to nit-pick, but the FAF on an ILS is the glideslope intercept. GS intercept is usually at or near the marker, but it isn't always.

Greg

I don't think this is entirely true.

Case in point, ILS 25L at KLAX and ILS 25L at KLAS. For LAX, the IAF is at FUELR, which is 26nm from the field. The outer marker for LAX is LIMMA, which is 7nm out. I can guarantee you'll intercept the glideslope before LIMMA.

Same would suffice for Las Vegas, where PRINO is the IAF for 25L, and that's 21nm out. You'll have both the localizer and glideslope prior to even getting to that fix.

I'll agree it isn't always true, because there may not be an outer, middle, or inner marker for a given ILS approach, such as Vegas. But I'm definitely positive you'll have both LOC and GS before the FAF.

BL.
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Jason
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« Reply #2 on: March 31, 2008, 08:52:31 PM »

Not to nit-pick, but the FAF on an ILS is the glideslope intercept. GS intercept is usually at or near the marker, but it isn't always.

Greg

I don't think this is entirely true.

Case in point, ILS 25L at KLAX and ILS 25L at KLAS. For LAX, the IAF is at FUELR, which is 26nm from the field. The outer marker for LAX is LIMMA, which is 7nm out. I can guarantee you'll intercept the glideslope before LIMMA.

Same would suffice for Las Vegas, where PRINO is the IAF for 25L, and that's 21nm out. You'll have both the localizer and glideslope prior to even getting to that fix.

I'll agree it isn't always true, because there may not be an outer, middle, or inner marker for a given ILS approach, such as Vegas. But I'm definitely positive you'll have both LOC and GS before the FAF.

BL.


LIMMA isn't an outer marker though, it's the non-precision (localizer) FAF defined by DME off of the localizer antenna (or SLI R-297 and the localizer course).  Regarding the ILS 25L at Las Vegas, the precision approach FAF is just about at RELIN intersection as noted by the lightning bolt symbol on the profile view.  You can still be vectored way outside of RELIN, but that is still the legal glideslope intercept (as charted).  You can intercept and follow the GS prior to this point, but you must be established on the GS by this point (hence, GS intercept).

I have to agree with Greg on this one.  Most of the precision FAFs (glide slope intercept) occur at or near the outer marker if one exists on the procedure.
« Last Edit: March 31, 2008, 08:57:32 PM by Jason » Logged
Greg01
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« Reply #3 on: March 31, 2008, 08:53:48 PM »

Tyketto,

The ILS 25L into LAX does not have marker beacon system. LIMMA is the FAF for the LOCALIZER 25L approach, not the ILS, hence the maltese cross in the profile view.

The FAF for the ILS is the GS intercept. Now, if you fly the approach as charted (basically ATC gets you established at or inside of HUNDA at 3200, you will capture the GS as charted. However, if they authorize 1900 between HUNDA and LIMMA, then you will pick up the GS at LIMMA. It just so happens with this approach that GS intercept will occur at LIMMA (again, if ATC authorizes 1900).

Again, not so for the LAS approaches. The explanation above for the LAX approach applies to the LAS approach. FAF for the ILS 25L into LAS is the GS intercept (the lightning bolt arrow on the profile view).

Now, I can explain why the LAX approach says: ILS or LOC 25L and the LAS approach only says: ILS 25L yet in still includes LOC only minimums...but it'll have to be tomorrow (have to hit the hay).

Respectfully,
Greg
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Greg01
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« Reply #4 on: March 31, 2008, 08:54:37 PM »

Jason, looks like we posted at about the same time.

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Jason
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« Reply #5 on: March 31, 2008, 09:25:39 PM »

Now, I can explain why the LAX approach says: ILS or LOC 25L and the LAS approach only says: ILS 25L yet in still includes LOC only minimums...but it'll have to be tomorrow (have to hit the hay).

This question made me think a little, too.  I honestly don't know the official answer, but my guess would be that it would allow the controller to issue a clearance for the localizer approach (ie, "cleared localizer runway 25L approach") rather than a clearance for the ILS with a GS unusable advisory (ie, "cleared ILS runway 25L, glide slope unusable").  I can't think of any TERPS requirements that would reflect a change in the title, but there certainly could be.
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KSYR-pjr
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« Reply #6 on: March 31, 2008, 10:16:29 PM »

I have to agree with Greg on this one.  Most of the precision FAFs (glide slope intercept) occur at or near the outer marker if one exists on the procedure.

I'll third this.  For us little retractable gear aircraft pilots, the FAF/glideslope intercept on an ILS is where we drop the gear and transition from the straight and level glideslope intercept altitude to a descent down the glideslope.  Dropping the gear on my Bonanza slows the aircraft from 153 (max gear down speed, or Vle) to 120 knots and, assuming proper power setting, naturally starts a 500 foot a minute descent with the glideslope due to the drag of the gear. 

My understanding is that the now old-fashioned outer marker is tied to the FAF on an ILS because it serves as the pilot's audio cue as to the intercept point.  As pointed out previously, though, most of the outer markers are being decommissioned across the US due primarily to (I believe) the cost savings of not having to maintain them.
« Last Edit: March 31, 2008, 10:18:05 PM by KSYR-pjr » Logged

Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
tyketto
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« Reply #7 on: April 01, 2008, 01:17:32 AM »

Tyketto,

The ILS 25L into LAX does not have marker beacon system. LIMMA is the FAF for the LOCALIZER 25L approach, not the ILS, hence the maltese cross in the profile view.

Are you sure about that?

http://www.airnav.com/airport/LAX/ils/25L

Quote
Outer marker information
                  Type: OUTER MARKER BEACON ONLY
                  Name: LIMMA
              Location: 33-56-53.500N / 118-16-32.200W
                        5.4 nm (32720 ft.) from the approach end of runway 25L

Quote
Again, not so for the LAS approaches. The explanation above for the LAX approach applies to the LAS approach. FAF for the ILS 25L into LAS is the GS intercept (the lightning bolt arrow on the profile view).

I'll agree on that, but what I was getting at is that you'll get the GS intercept much further out than that, not just only at the FAF, which is what I think you may have been alluding to before. I've had it pick up out by PRINO and CROWE, which are at least 20DME from the field.

BL.
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Jason
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« Reply #8 on: April 01, 2008, 06:32:48 AM »

Are you sure about that?

http://www.airnav.com/airport/LAX/ils/25L

Quote
Outer marker information
                  Type: OUTER MARKER BEACON ONLY
                  Name: LIMMA
              Location: 33-56-53.500N / 118-16-32.200W
                        5.4 nm (32720 ft.) from the approach end of runway 25L

The AirNav data is old, it still has the outer marker designation for most of these fixes even though the system no longer exists.  Even if the antenna exists and the system is operational, but unmonitored, legally, it can't be used on the approach because the marker beacon is neither monitored or charted.

Quote
Again, not so for the LAS approaches. The explanation above for the LAX approach applies to the LAS approach. FAF for the ILS 25L into LAS is the GS intercept (the lightning bolt arrow on the profile view).

I'll agree on that, but what I was getting at is that you'll get the GS intercept much further out than that, not just only at the FAF, which is what I think you may have been alluding to before. I've had it pick up out by PRINO and CROWE, which are at least 20DME from the field.

BL.


I don't think we're talking about actual GS intercept, we're talking about the ILS (precision approach) FAF, which is the glideslope intercept, as indicated by the location of the lightning bolt on the profile view of the procedure.
« Last Edit: April 01, 2008, 07:25:20 AM by Jason » Logged
Jason
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« Reply #9 on: April 01, 2008, 07:25:43 AM »

I've split this thread from the original, since it doesn't necessarily apply to that discussion.
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KSYR-pjr
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« Reply #10 on: April 01, 2008, 07:39:48 AM »

I'll agree on that, but what I was getting at is that you'll get the GS intercept much further out than that, not just only at the FAF, which is what I think you may have been alluding to before. I've had it pick up out by PRINO and CROWE, which are at least 20DME from the field.

When a controller is vectoring an aircraft to an ILS they are descending and vectoring so that the aircraft intercepts the glideslope at or very near the FAF, not some point 20 miles out.  I would need to look it up, but I am not even sure a glideslope indication could be trusted that far out.
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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
KSYR-pjr
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« Reply #11 on: April 01, 2008, 08:52:18 AM »

Found the information about glideslope usability from the US AIM:

http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/Chap1/aim0101.html
Quote
3. The glide path projection angle is normally adjusted to 3 degrees above horizontal so that it intersects the MM at about 200 feet and the OM at about 1,400 feet above the runway elevation. The glide slope is normally usable to the distance of 10 NM. However, at some locations, the glide slope has been certified for an extended service volume which exceeds 10 NM.

Personally I don't know what markings there are on a chart that indicate a GS is usable beyond 10NM since I have never required it.  I would be curious what scenario is in place that requires a GS to be usable at a range of 20nm.
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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
tyketto
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« Reply #12 on: April 01, 2008, 01:47:30 PM »

Found the information about glideslope usability from the US AIM:

http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/Chap1/aim0101.html
Quote
3. The glide path projection angle is normally adjusted to 3 degrees above horizontal so that it intersects the MM at about 200 feet and the OM at about 1,400 feet above the runway elevation. The glide slope is normally usable to the distance of 10 NM. However, at some locations, the glide slope has been certified for an extended service volume which exceeds 10 NM.

Personally I don't know what markings there are on a chart that indicate a GS is usable beyond 10NM since I have never required it.  I would be curious what scenario is in place that requires a GS to be usable at a range of 20nm.

Try looking at the CIVET5 or RIIVR1 arrivals into LAX. The localizer (from what I've asked of pilots) goes out that far, but they have said that they capture the glideslope at FUELR or PALAC, which both are about 25DME from the field. This is why the controlers at SoCal give the call 'After FUELR (PALAC), Cleared ILS runway 25L (24R) approach.' No true TAC required for the approach clearance. By the time they hit FUELR, they should have both and descend by it, as the STARs end at the IAF for the ILS approach.

theoretically, you could wash/rinse/repeat for KEPEC2/SUNST2/TYSSN2 into LAS, as those arrivals drop you off at the IAF for ILS 25L as well. So by then, you'd have to have the GS active, otherwise, you wouldn't descend any lower than what you're given in PTAC until roughly 10NM out, right?

BL.
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KSYR-pjr
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« Reply #13 on: April 01, 2008, 02:23:57 PM »

This is why the controlers at SoCal give the call 'After FUELR (PALAC), Cleared ILS runway 25L (24R) approach.'

Don't have time right now to really study the specific chart (will do soon) but in general, controllers clearing an aircraft for an approach does not demonstrate that the aircraft has captured the glideslope (which I believe is what this discussion is about). 

Rather, controllers clear aircraft for the ILS approach when they become established on the localizer, and that does have a much further usable range than the glideslope.  Once cleared for the approach, the pilot is free to descend to the minimum altitude(s) detailed on the chart for that segment of the approach, if not given a crossing restriction, that is.

Also, from what I understand (not being a pilot who flies into the major airports via STARs I am forced to extrapolate) an approach clearance trumps a STAR procedure.  In other words, once the pilot is cleared for the approach he/she would adhere to altitudes, headings, etc, using the approach plate, not the STAR.

Do aircraft really capture the glideslope 25nm out for LAX?  I am not so sure about that.  Take a look at the profile section of 25L into LAX:



I would have expected to see the glideslope drawn out to FUELR had the approach designers intended the GS be captured there.  I could be wrong but that is my interpretation of the chart.

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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
DairyCreamer
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« Reply #14 on: April 01, 2008, 03:52:42 PM »

When a controller is vectoring an aircraft to an ILS they are descending and vectoring so that the aircraft intercepts the glideslope at or very near the FAF, not some point 20 miles out.  I would need to look it up, but I am not even sure a glideslope indication could be trusted that far out.

I'm afraid you don't seem terribly familiar with major international airports during busy rushes then.

Look over at DEN and their Triple Simo ILSs.  Look at ILS Runway 35L.  Find CRUUP.  19.8 DME south of the runway... and ATC must issue instructions for aircraft to be established on the localizer outside of that point by at least one mile.  During a busy rush in poor weather, people might well be joining that localizer up to 30 NM out.  And I guarantee those pilots are recieving the glideslope info by the time they hit CRUPP, probably much earlier.  It's a requirement to run simos.

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."

~Nate
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