ILS GS intercept

[genna]

So,

I had a discussion with my instructor about how to properly fly this(and probably most) ILS approach when it comes to intercepting the glideslope

http://skyvector.com/files/tpp/1505/pdf/05089IL23.PDF

Assuming flying the full procedure from Westminster VOR as the IAF and being cleared for the approach before intercepting the localizer. Once I intercept the localizer, do I:
1. Descend to and maintain 1700 to intercept the glideslope or
2. Stay at 2800 until GS intercept and then do a GS descend to DA

I'm of the #1 opinion, but my instructor is of the #2.

From what I remember from IFR Written, 1700 is the GS intercept altitude.

ps when you intercept the localizer, you are under the GS @2800, but not very far under.

 

[Checkout_my_Six]

what does the plate say?.....and do that.

definitely don't descend before the plate says.

 

[Palmpilot]

I think it's purely a matter of personal preference on that approach.

The only situation I have heard of where you shouldn't intercept the glideslope early is if it's an approach that has stepdown fixes farther out on the localizer. In that case, being on the glideslope can sometimes cause you to be below the stepdown altitude.

 

[nosehair]

It is your choice. It is easier to intercept the GS at 2800 and make one descent configureration change and be well established on GS as you cross faf which is where you get the freq change to tower .
You could descend immediately to 1700 at completion of PT if u wanted to.
For instance if the reported ceiling is 2000 and you want to break out and continue on a visual.

 

[aterpster]

I think it's purely a matter of personal preference on that approach.

The only situation I have heard of where you shouldn't intercept the glideslope early is if it's an approach that has stepdown fixes farther out on the localizer. In that case, being on the glideslope can sometimes cause you to be below the stepdown altitude.

Spot on.

 

[Gucci Pilot]

You can intercept the glideslope from further out than the "Glide slope intercept" point(RICKE). Glide slope service area is usually out to 10 nm. Doing it that way makes for a more stable approach and less of the stair stepping

 

[Checkout_my_Six]

I fly this at 2,800 until established. I see no benefit going lower early.

 

[genna]

I fly this at 2,800 until established. I see no benefit going lower early.

I've seen one benefit. Autopilot at least once had missed the GS intercept. I guess it happened because it came very quickly after the turn and it had not quite locked the localizer course yet. That's more of a guess though and may be completely unrelated.

 

[luvflyin]

i'd just pickup the glide slope out there by NUMBE and check that I was close to 1700 at RICKE to make sure I hadn't been following a false glide slope down. On any approach you have to comply with any minimum, maximum or mandatory altitudes for any step down fixes outside the final approach segment. Sometimes this may require you to be above the glide slope out there. Not an issue on this approach. There were problems with pilots following the glide slope down from to far out and busting altitudes on step down fixes. Usually a problem when it's cold out. While the cold doesn't affect the glide slope it does affect the altimeter. The problems were happening where those step down altitudes were used to separate airplanes from each other mostly with simultaneous ILS Approaches where planes are close to each other. The plane following the glideslope down and getting under the minimum altitude for that segment was getting to close to the plane for the parallel localizer who was at an assigned altitude during vector to final

 

[genna]

....There were problems with pilots following the glide slope down from to far out and busting altitudes on step down fixes. Usually a problem when it's cold out. While the cold doesn't affect the glide slope it does affect the altimeter. The problems were happening where those step down altitudes were used to separate airplanes from each other mostly with simultaneous ILS Approaches where planes are close to each other. The plane following the glideslope down and getting under the minimum altitude for that segment was getting to close to the plane for the parallel localizer who was at an assigned altitude during vector to final

That's interesting, I had not even thought about it. If it's very hot out, RICKE and GS stay where they are, but the altimeter will show lower altitude @GS @ RICKE. If I'm flying perfect GS from far back, I will bust 1700 on the altimeter(I'm ok in reality) a little before RICKE.

 

[kjwalker01]

You could descend immediately to 1700 at completion of PT if u wanted to.

PT? With Westminster as the IAF? I don't think so. The Procedure Turn is for using Ricke as the IAF.

 

[aterpster]

PT? With Westminster as the IAF? I don't think so. The Procedure Turn is for using Ricke as the IAF.

If you were using Westminster as the IAF, you wouldn't be doing the procedure turn. If you do the procedure turn from over RICKE you can elect to immediately go down to 1,700 intercepting the localizer upon completion of the procedure turn.

 

[Unit74]

Based on that plate, I'd intercept the GS at 2800', get set up and stabilized farther out. Trying to get trimmed up at Ricke you only have 4.2 miles and in my opinion, your making the approach more stressful. Or in other words, your messing around trying to get
Stabilized when you could be talking about your missed approach procedure.

 

[flyingron]

Eh? If you are trimmed up in level flight in your approach configuration, changing to the glideslope descent configuration should be minor and typically doesn't involve changing too much. In my plane all I have to do is drop the gear and 10 degrees of flaps. Four miles in landing configuration is a long time in most small aircraft.

 

[aterpster]

Based on that plate, I'd intercept the GS at 2800', get set up and stabilized farther out. Trying to get trimmed up at Ricke you only have 4.2 miles and in my opinion, your making the approach more stressful. Or in other words, your messing around trying to get
Stabilized when you could be talking about your missed approach procedure.

I'd do the same. But, a pilot has the option to descend to 1,700 then intercept the G/S.

 

[luvflyin]

That's interesting, I had not even thought about it. If it's very hot out, RICKE and GS stay where they are, but the altimeter will show lower altitude @GS @ RICKE. If I'm flying perfect GS from far back, I will bust 1700 on the altimeter(I'm ok in reality) a little before RICKE.

Oops. Right, when it's hot out, not cold like I first said. You are OK in the reality of being separated from the rocks but may not be in the reality of being separated from other airplanes. Read AIM 5-4-5 b. Don't forget the notes. The glideslope is intended to be intercepted at the glideslope intercept altitude. I think that's probably the point your instructor was making.

After NUMBE you gotta start down. You gotta decide at what rate to do it. You can do the math (ok, I got this far to lose this much altitude I that much time but don,t forget the wind and ground speed versus airspeed etc etc). Just using the Glideslope out there as my aid in descending along that segment is how I'd do it. Just remember that beyond that point where the Glideslope Intercept lightning bolt is, the altitudes on the plate for that segment have priority over the needle.

 

[taters]

1700 is officialy the official altitude to intercept.....so on a checkride I would decend to 1700..in real world ops I would normally intercept from my last altitude assuming the GS signal jives...

 

[SCCutler]

I see nothing on that plate which authorizes descent below 2800' other than when you are on the Localizer. NB: If you are flying the PT, the 2800' minimum applies until you are aligned (229* inbound); the No PT, starting at the Westminster VOR, has you intercepting the Localizer 6.1 NM prior to the FAF, so you would not expect to intercept the Localizer until around 3.5 NM outside RICKE (the FAF); hence, plenty of time on the LOC before GS intercept.

 

[luvflyin]

1700 is officialy the official altitude to intercept.....so on a checkride I would decend to 1700..in real world ops I would normally intercept from my last altitude assuming the GS signal jives...

I'd officially intercept at 1700 to. And it would be a real easy, stabilized intercept. I'd already be there after having used the glideslope out there as an aid in the descent. I'm sure his instructor knows the examiners in the area and what they are looking for. Maybe it's chop, drop, level off, intercept. Not very in keeping with the concept of stabilized approaches thought. I'd say that during the oral portion of the checkride is the time to find out if someone understands the charts and knows the rules. As long as someone doesn't come away from the whole experience thinking that they have to always chop, drop, level off, intercept I guess it's all good.

 

[SCCutler]

Am I just nuts here? 1700' is not the Glideslope intercept altitude; it is a cross-check altitude at the FAF, and you should descend no lower than 1700' until you pass RICKE.

You should maintain the altitudes depicted in the procedure, *until* Glideslope intercept, then follow the GS down. Why would you do otherwise?

 

[frfly172]

Intercept 2800 at numbe,start down when established , cross ricke at 1700.

 

[MAKG1]

Am I just nuts here? 1700' is not the Glideslope intercept altitude; it is a cross-check altitude at the FAF, and you should descend no lower than 1700' until you pass RICKE.

You should maintain the altitudes depicted in the procedure, *until* Glideslope intercept, then follow the GS down. Why would you do otherwise?

You're missing the 1700 MSL stepdown prior to RICKE. Once you have intercepted the localizer, not the glideslope, your minimum altitude drops. There is a hold above RICKE and the missed approach goes there at 2800 so you being at a higher altitude a few miles ahead might be inconvenient for someone else who just went missed in IMC or who is using RICKE as IAF.

As for a stabilized approach, sure that's true, but you're still outside the FAF, and more than 1500 AGL.

 

[John Collins]

Am I just nuts here? 1700' is not the Glideslope intercept altitude; it is a cross-check altitude at the FAF, and you should descend no lower than 1700' until you pass RICKE.

You should maintain the altitudes depicted in the procedure, *until* Glideslope intercept, then follow the GS down. Why would you do otherwise?

1700 is the GS intercept altitude. It is also a minimum altitude for the segment. You may be higher, but not lower. On a "localizer only" approach, you must cross the FAF at the minimum of 1700 MSL. On a full ILS approach, once the GS is intercepted on the segment that contains the GS intercept, the 1700 minimum no longer applies, the GS rules, so dependent on temperature, you may cross above or below RICKE at 1700 MSL.

I am lazy and would intercept the GS at 2800 feet. Passing NUMBE intersection, the nominal GS is at 3733 feet or 933 feet above the 2800 crossing minimum. I would not expect to intercept the GS for roughly another 3 NM or 90 seconds assuming a ground speed of 120 Kts. Crossing RICKE, I would cross check my altitude to be 1700+/- 150 feet. On a 30 degree C day (86 F) at the airport, with a perfect altimeter that is set properly and all equipment working, dead on the GS, the altimeter would read 1631 feet. If it was a blistering 40 C (104 F) at the airport, then the altimeter would read 1594 feet.

 

[flyingron]

One problem with this approach compared to other approaches is there are multiple things going on at 1700 over RICKE that are somewhat "coincidental."

First the Maltese Cross indicates that RICKE is the FAF for the non-precision approach.

The UNDERLINED 1700 indicates that you have to be at or above 1700 on that side of RICKE (when not on the gs).

The lightning bolt from 1700 to the glideslope indicates that 1700 is the published glide slope intercept altitude which is by definition the FAF for the precision approach.

The small 1700 above the maltese cross (which really in my mind should be closer to the cross rather than where it is currently drawn) is the altitude that the glide slope crosses RICKE.

Below is a profile view from an approach where things aren't all lined up like that:

Note here, the published glide slope intercept (and hence precision FAF) is 3000. The non precision FAF is at TWITY and the glideslope crosses there at 2489 even though the non-precision minimum altitude is 2500 until that point.

Then it gets really fun when the approach designers designate multiple glide slope intercept altitudes.

 

[John Collins]

Then it gets really fun when the approach designers designate multiple glide slope intercept altitudes.

I thought all of these have been removed?

 

[aterpster]

I thought all of these have been removed?

The ones I am familiar with have been corrected.

 

[taters]

I thought all of these have been removed?

I think in DTW there are still some of those published...

 

[Palmpilot]

One problem with this approach compared to other approaches is there are multiple things going on at 1700 over RICKE that are somewhat "coincidental."

First the Maltese Cross indicates that RICKE is the FAF for the non-precision approach.

The UNDERLINED 1700 indicates that you have to be at or above 1700 on that side of RICKE (when not on the gs).

The lightning bolt from 1700 to the glideslope indicates that 1700 is the published glide slope intercept altitude which is by definition the FAF for the precision approach.

The small 1700 above the maltese cross (which really in my mind should be closer to the cross rather than where it is currently drawn) is the altitude that the glide slope crosses RICKE.

Below is a profile view from an approach where things aren't all lined up like that:

Note here, the published glide slope intercept (and hence precision FAF) is 3000. The non precision FAF is at TWITY and the glideslope crosses there at 2489 even though the non-precision minimum altitude is 2500 until that point.

Then it gets really fun when the approach designers designate multiple glide slope intercept altitudes.

One thing that's interesting about the minimum altitudes on approach plates is that the Instrument Rating PTS treats some of them as if they were not minimum altitudes; on the ones prior to the final approach segment, it only requires the applicant to maintain altitude +/- 100 feet, not +100/-0.

 

[genna]

One problem with this approach compared to other approaches is there are multiple things going on at 1700 over RICKE that are somewhat "coincidental."

First the Maltese Cross indicates that RICKE is the FAF for the non-precision approach.

The UNDERLINED 1700 indicates that you have to be at or above 1700 on that side of RICKE (when not on the gs).

The lightning bolt from 1700 to the glideslope indicates that 1700 is the published glide slope intercept altitude which is by definition the FAF for the precision approach.

The small 1700 above the maltese cross (which really in my mind should be closer to the cross rather than where it is currently drawn) is the altitude that the glide slope crosses RICKE.

Below is a profile view from an approach where things aren't all lined up like that:

Note here, the published glide slope intercept (and hence precision FAF) is 3000. The non precision FAF is at TWITY and the glideslope crosses there at 2489 even though the non-precision minimum altitude is 2500 until that point.

Then it gets really fun when the approach designers designate multiple glide slope intercept altitudes.

Yes. It's very clear on your example. In my case, looking at profile, there is a descent from 2800 to 1700 shown from NUMBE to RICKE. For all I know, GS can be unreliable that far out

I understand the reasons why it may be beneficial to stay at 2800 to intercept, but that's not what the plate says.

In any case. I guess it's my choice since I know this approach . As long as Either is ok to do.

 

[Palmpilot]

I understand the reasons why it may be beneficial to stay at 2800 to intercept, but that's not what the plate says.

Note however that the plate does not rule out staying at 2800 to intercept, because it says to fly at or above 1700. If it were a mandatory altitude, there would be lines both above and below the 1700.

 

[Unit74]

Eh? If you are trimmed up in level flight in your approach configuration, changing to the glideslope descent configuration should be minor and typically doesn't involve changing too much. In my plane all I have to do is drop the gear and 10 degrees of flaps. Four miles in landing configuration is a long time in most small aircraft.

I'm not that good. I'll take the extra time.

 

[flyingron]

I'm not that good. I'll take the extra time.

You should read Peter Dogan's book. He divides the instrument flight into a half a dozen regimes including things like "approach level", "non-precision descent" and "precision descent". Once you intercept the localizer on the PT here you'd do the non-precision descent (about 800 fpm) down to 1700 and then go back to the approach level. Once then needles come to the donut, you do the precision descent. Only slight tweaks are needed after that to keep the needle centered.

 

[John Collins]

Yes. It's very clear on your example. In my case, looking at profile, there is a descent from 2800 to 1700 shown from NUMBE to RICKE. For all I know, GS can be unreliable that far out

I understand the reasons why it may be beneficial to stay at 2800 to intercept, but that's not what the plate says.

In any case. I guess it's my choice since I know this approach . As long as Either is ok to do.

One should consider the standard service volume of the GS, which is 10 NM. By the time you intercept the GS, you will be inside the service volume and approximately 7 NM. the total length of the leg is 10.3 NM, but by the time you are centered on the localizer, you are inside the service volume of the GS.

 

[aterpster]

One should consider the standard service volume of the GS, which is 10 NM. By the time you intercept the GS, you will be inside the service volume and approximately 7 NM. the total length of the leg is 10.3 NM, but by the time you are centered on the localizer, you are inside the service volume of the GS.

If you have a G/S OFF flag, then your only option is make a barometric descent to 1,700.

 

[poadeleted20]

I had a discussion with my instructor about how to properly fly this(and probably most) ILS approach when it comes to intercepting the glideslope

http://skyvector.com/files/tpp/1505/pdf/05089IL23.PDF

Assuming flying the full procedure from Westminster VOR as the IAF and being cleared for the approach before intercepting the localizer. Once I intercept the localizer, do I:
1. Descend to and maintain 1700 to intercept the glideslope or
2. Stay at 2800 until GS intercept and then do a GS descend to DA

Since there's no maximum altitude (overline) indication, it's your choice.

I'm of the #1 opinion, but my instructor is of the #2.

You're both right, and neither of you is wrong. Personally, I prefer #2 because it's easier just to drive to the GS and start down than to leave 2800, level off at 1700, and then drive to the GS and descend. However, that's a question of technique, not procedure.

From what I remember from IFR Written, 1700 is the GS intercept altitude.

That's the textbook answer for the written, but it's not a mandatory procedure.

ps when you intercept the localizer, you are under the GS @2800, but not very far under.

You should be about 600 below the GS when you roll out on the localizer inside NUMBE, and that's not what I'd call "not very far under", but that's a very subjective issue either way.

 

[poadeleted20]

I've seen one benefit. Autopilot at least once had missed the GS intercept. I guess it happened because it came very quickly after the turn and it had not quite locked the localizer course yet. That's more of a guess though and may be completely unrelated.

More likely you were late hitting the APPROACH button on the autopilot, but I'd need to know exactly what avionics were involved and what your buttonology was to be more certain.

 

[azure]

Am I just nuts here? 1700' is not the Glideslope intercept altitude; it is a cross-check altitude at the FAF, and you should descend no lower than 1700' until you pass RICKE.

The profile view only shows the descent to 1700 after turning inbound from the PT, but on the plan view, the segment from NUMBE to RICKE is charted at 1700, so if already established inbound, you can descend from 2800 after crossing NUMBE -- *if* cleared to do so, of course.

 

[aterpster]

The profile view only shows the descent to 1700 after turning inbound from the PT, but on the plan view, the segment from NUMBE to RICKE is charted at 1700, so if already established inbound, you can descend from 2800 after crossing NUMBE -- *if* cleared to do so, of course.

If you weren't free to do it either way, then ATC would have to issue a restriction with the approach clearance, which is not likely at this location.

 

[poadeleted20]

The profile view only shows the descent to 1700 after turning inbound from the PT, but on the plan view, the segment from NUMBE to RICKE is charted at 1700, so if already established inbound, you can descend from 2800 after crossing NUMBE -- *if* cleared to do so, of course.

As is normal, the profile view shows only the altitudes for the course reversal route. You have to look at the planform view for the altitudes to fly on a feeder route entry. So, if cleared for the approach from EMI (e.g., "Cessna 123 is 5 miles from Westminster, maintain [altitude] until established, cleared ILS 23 approach"), you already have your clearance to fly to EMI, then from EMI to NUMBE at 2800, and then descend to 1700 once established on the localizer inside NUMBE without any further word from the controller.

 

[genna]

More likely you were late hitting the APPROACH button on the autopilot, but I'd need to know exactly what avionics were involved and what your buttonology was to be more certain.

KAP 140. I did not hit it late, but I was flying heading bug and forgot to switch to ROL before hitting apch btn. That turned the plane left to do 45 intercept. By the time it captured loc, the GS was already at middle, but AP never captured it