ILS Procedure question

[coflyer]

About the following ILS approach. My procedure to fly it would be PT outbound to 7000, PT inbound to 6600, then intercepting the GS.

My CFII's procedure is PT outbound to 7000, and keeping 7000 when PT inbound. Intercept the GS at 7000, and verify altitude (6533) at BUFFS LOM. It is shown as red line in the profile view.

My CFII's method makes sense as it only requires one throttle reduction instead of two after PT inbound.

However, I'm not sure if this is a regular method that is used by other pilots, or it meets FAA regulations. Could anyone comment? Thank you

 

[John Collins]

The 6600 altitude is depicted as the GS intercept altitude by the lightning bolt with the arrow head, but is shown as a minimum altitude that guarantees the aircraft will intercept the glidepath from below the GS. The normal GS service volume is within 10 NM of the threshold, although longer service volumes may be certified. Intercepting the GS at 7,000 feet MSL will occur nominally at 7.26 NM from the threshold, so it is not unreasonable to intercept the GS at this distance and altitude.

 

[LearDriver]

I would remain at 7000 and descend on glideslope once captured. Confirm the GS altitude at the fix to confirm you are on the proper glideslope. I find it easier to do it this way. It gives you more time to confirm your information and re-brief your DA(H) and missed approach procedure.

 

[midlifeflyer]

However, I'm not sure if this is a regular method that is used by other pilots, or it meets FAA regulations. Could anyone comment? Thank you

Unless the 6600 is a mandatory altitude (which would be shown by lines both above and below the number), you can remain as high as you want.

I don't see a particularly significant benefit or detriment to either method. And you'd want to verify your GS intercept altitude in either case.

 

[gismo]

I would remain at 7000 and descend on glideslope once captured. Confirm the GS altitude at the fix to confirm you are on the proper glideslope. I find it easier to do it this way. It gives you more time to confirm your information and re-brief your DA(H) and missed approach procedure.

Ditto. As depicted, 6600 would be safe and legal once established inbound but unless it were mandatory (lines above and below the numbers) a higher altitude can be flown. As John pointed out, flying much higher could have you above the glideslope depending on how far you went out on the PT and that won't work for glideslope capture on some autopilots but it would still be legal to do so (capture from above manually).

 

[John Collins]

The comparison of the altitude at the FAF is a good idea, but the altitude can easily vary by a few hundred feet and is just a crude cross check to detect errors that are way out of bounds. Temperature alone will account for a reading at ISA+/-20C of -/+ 121 feet. Add to this altimeter errors of +/- 50 feet, non standard pressure lapse rates, position errors of +/- .1 NM, allowable GS indication errors, and how close you are following the glideslope. These can add up. I am not suggesting not to do the comparison, but just because the altimeter and the GS differ by a 100 feet doesn't mean much. On a hot day, expect the cross check to show the altimeter too low and on a cold day, too high.

 

[Palmpilot]

One caviat is that if there are any stepdowns between the indicated glideslope intercept altitude and your actual glideslope intercept altitude, you are still responsible for making sure you stay at or above the stepdown altitudes, which is not guaranteed by being on the glide slope.

 

[matthammer]

The comparison of the altitude at the FAF is a good idea, but the altitude can easily vary by a few hundred feet and is just a crude cross check to detect errors that are way out of bounds. Temperature alone will account for a reading at ISA+/-20C of -/+ 121 feet. Add to this altimeter errors of +/- 50 feet, non standard pressure lapse rates, position errors of +/- .1 NM, allowable GS indication errors, and how close you are following the glideslope. These can add up. I am not suggesting not to do the comparison, but just because the altimeter and the GS differ by a 100 feet doesn't mean much. On a hot day, expect the cross check to show the altimeter too low and on a cold day, too high.

That sounds like an excellent reason to check the altitude at your FAF. If I'm on GS at the FAF, and my altimeter is showing 121' higher than it should on an ISA-20C day, I'm going to adjust my DA accordingly. Wouldn't want to unknowingly fly to a 79' DA without the runway environment in sight... :wink2:

 

[HPNPilot1200]

In this particular case, I would prefer to remain at 7,000 ft until intercepting the glideslope. I don't see any real benefit in descending 400 feet just to intercept the glideslope I would have intercepted already if I had just remained at 7,000 feet. It also gives you more time to set up for a stabilized approach and minimizes power changes.

One caviat is that if there are any stepdowns between the indicated glideslope intercept altitude and your actual glideslope intercept altitude, you are still responsible for making sure you stay at or above the stepdown altitudes, which is not guaranteed by being on the glide slope.

The FAA issued a bulletin (#11009) regarding just that earlier this year. Apparently folks were intercepting well outside the final approach segment and not complying with published step-down fixes while established on the glideslope (particularly in warm/hot weather). It's important to remember that you are still responsible for complying with published step-down fixes prior to the final approach segment on an ILS.

 

[somorris]

Hi Coflyer. I would fly the approach the same way you described you would (or prefer -- i.e. to 6600 inbound PT). I guess to each his own, but to me that is what is charted so that is what I would fly.

 

[jesse]

I'd go down to the 6600 and intercept there. Why? Because I'd rather just operate with consistency by flying what the chart says. Going down a little earlier might just cause me to break out earlier which I'm fine with too.

Yes in this case you can stay at 7,000 then intercept and follow down. But you won't be able to do this in all cases. You need to really look at the plate to determine if you can/can't do that. That consumes some of the available brain bandwidth.

I teach instrument students to be consistent and to keep it simple and avoid tricks. It's funny - nearly every student I get at some point will start to do something that requires a little more brain power then is needed and they get away with it. Something about it might seem "easier" to them. The moment always comes though where they regret going down that road. They get loaded up and they screw up because of their "trick".

So to sum this all up:
Be careful about doing things that aren't consistent with how you operate. If you generally always descend as the chart indicates - and you start to make exceptions to that - you may regret that someday. The moment you get too comfortable is the moment before everything falls apart.

 

[poadeleted20]

Yes in this case you can stay at 7,000 then intercept and follow down. But you won't be able to do this in all cases. You need to really look at the plate to determine if you can/can't do that.

Let's remember that the GS is, unless otherwise marked, only reliable out to 10 miles. If you try to intercept outside 10nm and follow it down when the lightning bolt symbol doesn't direct such, you could be following an unreliable signal even if you have a good needle and the flag is out of sight. OTOH, hitting the altitudes on the chart guarantees not only good guidance but also both obstruction and procedural clearance all the way.

And keep in mind that there are some approaches with a "not above" (line over the top) as opposed to a "hard" altitude (lines above and below) in order to keep you below an overlying crossing procedure. The usually have you below the electonic GS outside the lightning bolt point, and following the GS outside that point may put you above that "not above" altitude in conflict with overlying traffic. You may also see "block" altitudes looking something like this:
____
4000
3300

Stay between those two altitudes even if that puts you off the GS!

 

[dell30rb]

On that approach, if you are coming from the GILL vor, you hit the IAF at 7000 feet and then proceed outbound on the localizer course. Must you wait until you hit the WELDS IF to initiate the procedure turn?

Also, the WELDS and BUFFS are labeled with a distance fix and RADAR yet I do not see DME or RADAR or ADF required listed on the plate. Do you still have to identify the fix by one of these methods?

 

[poadeleted20]

On that approach, if you are coming from the GILL vor, you hit the IAF at 7000 feet and then proceed outbound on the localizer course. Must you wait until you hit the WELDS IF to initiate the procedure turn?

No. The PT is based on BUFFS, not WELDS, and when doing the PT, the IF is effectively interception of the LOC inbound. WELDS is only an IF if arriving from WAVDI on the GLL 17.5 DME arc or getting vectors to final and joining the LOC outside WELDS.

And if flying this via the arc from WAVDI, y'all be careful to switch your DME from GLL VOR to I-DCI LOC when joining the LOC, because the WELDS and BUFFS DME fixes are based on DME off I-DCI, not GLL.

Also, the WELDS and BUFFS are labeled with a distance fix and RADAR yet I do not see DME or RADAR or ADF required listed on the plate. Do you still have to identify the fix by one of these methods?

No. If you don't have radar monitoring, DME, or ADF, you can use your marker beacon receiver on the OM to fix your passage of BUFFS outbound, and WELDS is only an issue for the DME arc from WAVDI (which means you'd have to have DME) or vectors to final joining outside WELDS (in which case ATC can call it).

 

[dell30rb]

Thanks

 

[hanklehrer]

While I have not been an active CFII for many years, if you leave 7000 after the PT and before intercepting the GS, this would require a pitch/power change. If you decide to do so and reach 6600 and have not intercepted the GS, another change in configuration would be needed. Then when the GS is finally intercepted, you would have another change to begin your stabilized configuration for the continuation of the approach.

It seems to me that too much work will be required. Configure just once and then fine tune. A lot of times on retractables, you can just drop the gear on GS intercept and the airplane minds pretty well.

HRL
ATP, CFII, CE500

 

[poadeleted20]

While I have not been an active CFII for many years, if you leave 7000 after the PT and before intercepting the GS, this would require a pitch/power change. If you decide to do so and reach 6600 and have not intercepted the GS, another change in configuration would be needed. Then when the GS is finally intercepted, you would have another change to begin your stabilized configuration for the continuation of the approach.

It seems to me that too much work will be required. Configure just once and then fine tune. A lot of times on retractables, you can just drop the gear on GS intercept and the airplane minds pretty well.

In general, I agree with Hank for exactly the reasons he stated. However, as mentioned above, if you do that, you must check that you'll be within the GS service volume and that you won't bust any altitude restrictions.

 

[jesse]

In general, I agree with Hank for exactly the reasons he stated. However, as mentioned above, if you do that, you must check that you'll be within the GS service volume and that you won't bust any altitude restrictions.

Which is why I don't teach people to do it. I've found that someone's abilities to understand those "gotchas" aren't nearly as great as they often think they are.

I can explain the technical details of what you can and can't do on an approach plate and that person that explain that back to me understanding it in full detail. Ten minutes later in the airplane they screw it up.

Which is why I teach the pilot to be consistent and to base that consistency on procedures and technique that require the least amount of "if statements".

I've seen people that are very good at handling if statements and I let them operate that way. But I've also seen that bite them in the ass and then they start to have more faith in my keep it simple routine.

 

[tonycondon]

dang i learn something new every day. i've always just done one descent instead of breaking it up into pieces. but i always cross check the altitude on GS at FAF.

 

[poadeleted20]

Which is why I don't teach people to do it. I've found that someone's abilities to understand those "gotchas" aren't nearly as great as they often think they are.

I can explain the technical details of what you can and can't do on an approach plate and that person that explain that back to me understanding it in full detail. Ten minutes later in the airplane they screw it up.

Which is why I teach the pilot to be consistent and to base that consistency on procedures and technique that require the least amount of "if statements".

I've seen people that are very good at handling if statements and I let them operate that way. But I've also seen that bite them in the ass and then they start to have more faith in my keep it simple routine.

I guess it depends on whether the trainee is studying instrument procedures at the BS or PhD level. Follow the procedures as printed until you learn enough to know when it's OK to fliddle with them.

 

[Palmpilot]

In general, I agree with Hank for exactly the reasons he stated. However, as mentioned above, if you do that, you must check that you'll be within the GS service volume and that you won't bust any altitude restrictions.

Since the OP's scenario involved a PT, does anyone know of PTs that have intermediate stepdowns between them and the depicted glide slope interception point, or PTs that are outside the GS service volume?

I'm the one who brought up the stepdown issue in this thread, but now I'm wondering if it is really applicable to the OP's scenario.

 

[dell30rb]

I guess it depends on whether the trainee is studying instrument procedures at the BS or PhD level. Follow the procedures as printed until you learn enough to know when it's OK to fliddle with them.

As an instrument student, I definitely agree with that. Flying the plane is the easy part. I've been doing that for awhile. Learning to decipher a whole new set of rules / procedures is what is really taking my focus now.

 

[COFlyBoy]

Here's what I found in the Instrument Procedure Handbook:

"Another important altitude that should be briefed

during an IAP briefing is the FAF altitude, designated
by the cross on a nonprecision approach, and the lightning
bolt symbol designating the glide slope intercept
altitude on a precision approach. Adherence to and
crosscheck of this altitude can have a direct effect on​

the success of an approach.
...
The glide slope intercept altitude of a precision

approach should also be included in the IAP briefing.
Awareness of this altitude when intercepting the glide
slope can ensure the flight crew that a “false glide
slope” or other erroneous indication is not inadvertently
followed. Many air carriers include a standard
callout when the aircraft passes over the FAF of the
nonprecision approach underlying the ILS. The pilot
monitoring (PM) states the name of the fix and the
charted glide slope altitude, thus allowing both pilots to
crosscheck their respective altimeters and verify the​

correct indications."

This doesn't really explain the 2 altitudes that are listed on the chart at the FAF though.

 

[midlifeflyer]

This doesn't really explain the 2 altitudes that are listed on the chart at the FAF though.

What "2 altitudes"? Are you talking about the 6600 and the 6533?

6600 is the lowest altitude to which you may descend outside of BUFFS until intercepting the glideslope. The 6533 is not a mandatory procedure altitude but an equipment cross-check - it's the altitude that your altimeter should read in standard conditions when crossing BUFFS with the GS needle centered.

 

[COFlyBoy]

What "2 altitudes"? Are you talking about the 6600 and the 6533?

6600 is the lowest altitude to which you may descend outside of BUFFS until intercepting the glideslope. The 6533 is not a mandatory procedure altitude but an equipment cross-check - it's the altitude that your altimeter should read in standard conditions when crossing BUFFS with the GS needle centered.

Yes, those are the ones I was referring to. The IPH doesn't describe the difference. That crosscheck is very coarse at best. I pick up the OM for about 10 seconds which renders any altitude estimate pretty much useless. Well, maybe it would tell you if your altimeter setting is off by 1 inch. So far this has only happened to me once.

I've flown the ILS at GXY umpteen times and I can't remember whether I flew it at 7000 or 6600.

 

[gismo]

That sounds like an excellent reason to check the altitude at your FAF. If I'm on GS at the FAF, and my altimeter is showing 121' higher than it should on an ISA-20C day, I'm going to adjust my DA accordingly. Wouldn't want to unknowingly fly to a 79' DA without the runway environment in sight... :wink2:

The altimeter error decreases as you get closer to the elevation of the reporting station you got that altimeter setting from. If you're altimeter is off by 121 ft at 2000 AGL due to non-standard temps, it would only be off 12 ft at 200 AGL assuming you got the altimeter setting from a sensor on the field.

 

[poadeleted20]

Since the OP's scenario involved a PT, does anyone know of PTs that have intermediate stepdowns between them and the depicted glide slope interception point, or PTs that are outside the GS service volume?

This one, for starters -- you're beyond 10nm from the GS antenna if you reintercept the LOC more than 4 miles outside the PT reference point (BUFFS) and there's nothing to indicate an extended service GS volume.

 

[poadeleted20]

Addendum...

If you fly the PT on this approach at the depicted 7000, you will intercept the GS inside 10nm from the GS antenna (about 7.3 miles, I calculate). However, 7000 is a minimum, not a hard altitude. If you fly the PT higher (as is permitted, absent any ATC-given restriction), you may intercept the GS outside 10nm. And there are probably others where staying at the PT altitude will result in intercept outside 10.

 

[COFlyBoy]

Addendum...

If you fly the PT on this approach at the depicted 7000, you will intercept the GS inside 10nm from the GS antenna (about 7.3 miles, I calculate). However, 7000 is a minimum, not a hard altitude. If you fly the PT higher (as is permitted, absent any ATC-given restriction), you may intercept the GS outside 10nm. And there are probably others where staying at the PT altitude will result in intercept outside 10.

Ah, so then the question becomes is it unsafe, illegal, or otherwise bad to intercept the GS outside of the service volume?

Those reference altitudes do provide protection against capturing the false glideslope, but there is no depicted maximum altitude for the intercept.

Also, on that plate I noted that is says "remain within 10 nm", but it isn't explicit about what you are to reference that to. I would assume it is referenced to the BUFFS OM (the IAF). So one could stay within 10nm for the PT, and then try to intercept the GS while outside of its service volume.

 

[dell30rb]

Ah, so then the question becomes is it unsafe, illegal, or otherwise bad to intercept the GS outside of the service volume?

Those reference altitudes do provide protection against capturing the false glideslope, but there is no depicted maximum altitude for the intercept.

Also, on that plate I noted that is says "remain within 10 nm", but it isn't explicit about what you are to reference that to. I would assume it is referenced to the BUFFS OM (the IAF). So one could stay within 10nm for the PT, and then try to intercept the GS while outside of its service volume.

I'm sure we'll get a better answer from some of the instructors - but I think its no problem to intercept the glide slope outside the service volume. Just don't descend below the (minimum in this case - 6600) glide slope intercept altitude unless you are within 10nm of BUFFS

I think that "remain within 10nm" of BUFFS (and at or above the altitude) is done to ensure you stay within the service volume of the GS. And clear of obstacles / other traffic

 

[COFlyBoy]

I think that "remain within 10nm" (and at or above the altitude) is done to ensure you stay within the service volume of the GS.

I think the "stay within ..." is referenced to the IAF not the DME for the ILS. In which case you could be within 10nm of BUFFS, but well outside of the GS service volume.

 

[dell30rb]

Some glide slopes can be certified for longer distances than 10nm but now I think you are right - I think the 10nm of buffs is only for obstacle clearance

I suppose you could get screwed (with no dme) if you intercepted within 10nm of buffs but outside the service volume and started down on a false glideslope reading. But the crosscheck OM is near the minimum 6600 feet so if you didn't see the outer marker shortly after descending below that altitude you should know something is up.

 

[poadeleted20]

Ah, so then the question becomes is it unsafe, illegal, or otherwise bad to intercept the GS outside of the service volume?

I'm not going to debate semantics. Let's just say it's an improper procedure. If you want to do it properly, complete the PT within 10nm of BUFFS at or above 7000, establish yourself on the LOC inbound, descend to 6600, and intercept the GS.

Those reference altitudes do provide protection against capturing the false glideslope, but there is no depicted maximum altitude for the intercept.

It's actually the reverse -- false glideslopes will always be above, not below, the real one. That's a flight check requirement, and why you want to be sure you intercept from below inside the service volume.

Also, on that plate I noted that is says "remain within 10 nm", but it isn't explicit about what you are to reference that to.

That's always e anchor point of the PT, in this case BUFFS.

I would assume it is referenced to the BUFFS OM (the IAF). So one could stay within 10nm for the PT, and then try to intercept the GS while outside of its service volume.

One could, but that would not be the proper procedure.

 

[Palmpilot]

I'm not going to debate semantics. Let's just say it's an improper procedure. If you want to do it properly, complete the PT within 10nm of BUFFS at or above 7000, establish yourself on the LOC inbound, descend to 6600, and intercept the GS.

How is it an improper procedure? If you descend on the glideslope, aren't you descending to 6600? What difference does it make how you get to 6600, as long as you are above the depicted minimum altitude?

And once you get to 6600 on the glideslope, you are at the depicted intercept point, at which the depicted minimum altitude no longer applies.

 

[Palmpilot]

I suppose you could get screwed (with no dme) if you intercepted within 10nm of buffs but outside the service volume and started down on a false glideslope reading. But the crosscheck OM is near the minimum 6600 feet so if you didn't see the outer marker shortly after descending below that altitude you should know something is up.

According to this source, the first false glide slope is at twice the intended descent angle, so when you turned inbound from the procedure turn, your height above the airport would have to be more than twice that of the depicted glide slope interception point to hit one. You would then have to maintain twice the expected descent rate to hold it, which should be pretty obvious, I would think.

 

[gismo]

How is it an improper procedure? If you descend on the glideslope, aren't you descending to 6600? What difference does it make how you get to 6600, as long as you are above the depicted minimum altitude?

And once you get to 6600 on the glideslope, you are at the depicted intercept point, at which the depicted minimum altitude no longer applies.

I wouldn't call it an "improper" procedure either as long as you comply with the altitude restrictions. Services volumes are there to "guarantee" (sans malfunction) a usable signal at the stated distance from the ground station. Nothing I've ever seen dictates that you cannot follow any nav signal outside the appropriate SV just because you're outside that SV. That said, false GS signals do exist and any time you consider capturing one from above you should take steps to insure you've got the right (lowest) one. And FWIW, tracking a false GS won't lead you into the ground prematurely, the worst that can happen is the signal flags part way down, and/or is rough, and you might have to go missed on an approach that should have worked. Probably the most "interesting" false GS is the one that may exist at around twice the true GS, e.g. at 6°. Not only is the center of this GS pretty steep, the sensing is reversed (needle will go up if you're above and vice versa).

 

[COFlyBoy]

Right, by my calculations the first false GS would cross BUFFS at 8401 MSL. Seems like capturing the false GS is pretty unlikely for us NA bugsmashers. People with turbos or turbines may have a different experience.

I understand the comments about flying exactly what is on the plate. However, I'd prefer not to put a fast descent right before the GS intercept. In my novice experience, that will just result in a rather spectacular failure to capture the GS.

Also, I'd venture that the intermediate altitude is primarily for the LOC approach and is not required for the ILS. Similar to some of the RNAV approaches where there is an intermediate altitude that only applies to LNAV. Maybe one of our TERPS guys can shed some light.

 

[John Collins]

Also, I'd venture that the intermediate altitude is primarily for the LOC approach and is not required for the ILS. Similar to some of the RNAV approaches where there is an intermediate altitude that only applies to LNAV. Maybe one of our TERPS guys can shed some light.

Step downs outside the PFAF(FAF) must be complied with for both LPV and LNAV. Step downs between the FAF and the MAP onl need to be complied with on an LNAV approach. The same is true for an ILS or Localizer approach.

 

[poadeleted20]

I wouldn't call it an "improper" procedure either as long as you comply with the altitude restrictions.

The PTS would disagree, as it tells the examiner to fail you if you don't maintain the published altitude +/-100 feet outside the FAF on a SIAP. The published altitude after the PT is 6600. I believe there's a similar reference in the IPH, but I'm too tired to look it up right now.

 

[Jeanie]

What causes a false glide slope signal?