Maintain altitude until glide slope intercept or step down?

ClearedToThe said:
I can't believe this thread is 3 pages long already...

If ATC say's "maintain X,000ft until established" and you are not at X,000 ft, then you descend to X,000 ft and join the localizer. Once on the localizer descend as appropriate...

AIM
5-5-4. Instrument Approach
a. Pilot.
3. Upon receipt of an approach clearance while on an unpublished route or being radar vectored:
(b) Maintains the last assigned altitude until established on a segment of a published route or IAP, at which time published altitudes apply.

These PUBLISHED ALTITUDES can either be a MINIMUM altitude (as 99% of them are), or they can be a MANDATORY altitude. If it is a MINMUM altitude, you do not have to descend down to it because it is a...MINIMUM...not a mandatory altitude. Step down "manually" if you want to do more work than necessary, or stay at the last assigned altitude and ride the GS down and monitor your altitude to ensure you don't descend below the...minimum...altitudes along the localizer.
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I agree. I said that on page two.
 
Re: Maintain altitude until glide slope intercept or step do

To those of you who above believe this discussion is somehow invalid, I politely beg to differ. We are also talking about aircraft specific techniques, and I think that discussion has merit as well. Let's minimize the condescension, shall we?

In relation to the initial question, I have seen techniques taught by some 121 instructors who chastise their students for complying with the "maintain 3000 until established" clearance while on a vector, if 3000 is lower than the charted minimum safe/sector altitude or minimum vector altitude. This comes, in large part, due to a distrust of foreign ATC. As most of us know, in the US at least you should in fact descend to 3000 as soon as the controller tells you to. You can generally trust FAA ATC not to fly you into terrain. Elsewhere, it may in fact be wise to delay descent until on a published approach segment if your cleared altitude does not meet or exceed the aforementioned charted altitudes.

In addition, under certain atmospheric conditions you can and will bust altitudes on some approaches by following the glideslope alone. Here is an excerpt from a recent publication:

On ILS approaches, stepdown fixes are established for obstacle or traffic separation. Crewmembers are required to comply with all altitude restrictions (i.e., stepdown altitudes) prior to the final approach segment when cleared for an ILS approach.
Atmospheric temperature and pressure have no effect on the glide slope; it remains stationary. However, stepdown fixes are published for a pilot to fly using indicated altitude, which varies with temperature and pressure. Therefore, the proximity of stepdown fixes in reference to the glide slope, changes with the weather.

What this means to pilots is that on some approaches, outside the final approach segment, on a cool day, you might be able to follow the glide slope and all the published stepdown altitudes may pass below your aircraft. The next day, after a warm front passes, you could follow the same glide slope and (because the temperature is higher) those same stepdown altitudes now protrude into the glide slope; this requires pilot action to ensure compliance with the published minimum altitudes (stepdown fixes). On both days your flight path on the glide slope was the same, but on the warmer day, the stepdown altitude crept up into your glide path. High barometric pressure produces the same effect as high temperature.
Regardless of cause, pilots are cautioned to adhere to published step-down fixes located outside the final approach segment on an ILS approach. If pilots elect to follow the glide slope while outside the final approach segment they should be fully aware that this technique needs to be closely monitored and, if necessary, action taken to meet all stepdown altitudes. Examples of airports where multiple altitude deviations have occurred include, but are not limited to; LAX, ORD, ATL, and SLC.

All crewmembers must ensure that aircraft under their control, when cleared for approach, do not descend below published step-down altitudes while outside the final approach segment.
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The moral of the story is that you either need to be ready to intervene with another vertical mode if you see that the glideslope is going to take you below a restriction, or possibly use VNAV until the final approach segment.
 
Re: Maintain altitude until glide slope intercept or step do

Alchemy said:
To those of you who above believe this discussion is somehow invalid, I politely beg to differ. We are also talking about aircraft specific techniques, and I think that discussion has merit as well. Let's minimize the condescension, shall we?

In relation to the initial question, I have seen techniques taught by some 121 instructors who chastise their students for complying with the "maintain 3000 until established" clearance while on a vector, if 3000 is lower than the charted minimum safe/sector altitude or minimum vector altitude. This comes, in large part, due to a distrust of foreign ATC. As most of us know, in the US at least you should in fact descend to 3000 as soon as the controller tells you to. You can generally trust FAA ATC not to fly you into terrain. Elsewhere, it may in fact be wise to delay descent until on a published approach segment if your cleared altitude does not meet or exceed the aforementioned charted altitudes.
Click to expand...

Controllers could have a minimum vectoring altitude that could be lower than anything depicted on you charts, including the minimum safe altitude.

A weirder circumstance is being told to "decend and maintain" an altitude lower than the glide slope intercept altitude and then being told to "join.... cleared for the approach" prior to reaching the final approach fix. This situation as happened to me several times.
 
Re: Maintain altitude until glide slope intercept or step do

Its kind of dumb if you think about it. If the glideslope doesn't hit anything during one type of weather, its not going to hit anything during any other type.
 
Re: Maintain altitude until glide slope intercept or step do

ppragman said:
Its kind of dumb if you think about it. If the glideslope doesn't hit anything during one type of weather, its not going to hit anything during any other type.
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Only if the step down is a result of a ground obstruction. In many cases it is the result of departing traffic, so that if the weather is such that the actual glideslope will take you below the stepdown you may hit another airplane, or at least get closer than you would like to be to one.
 
Re: Maintain altitude until glide slope intercept or step do

KLB said:
Controllers could have a minimum vectoring altitude that could be lower than anything depicted on you charts, including the minimum safe altitude.

A weirder circumstance is being told to "decend and maintain" an altitude lower than the glide slope intercept altitude and then being told to "join.... cleared for the approach" prior to reaching the final approach fix. This situation as happened to me several times.
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I don't know if you've seen them but for some international destinations Jepp publishes a "minimum vector altitude" chart on something like a 10-1B page. It gives you the lowest altitudes that ATC is supposed to vector you to. In the US, yeah, you can generally trust the controllers. In Mexico, however, someitmes they give you a "descend to 3000 clearance cleared for the VOR/DME-2 approach" but what they really mean is "descend to 3000 AFTER you're established on the appropriate segement of the approach to go that low". As a result I always consulted the charted altitudes and made sure the clearance wasn't sending me below them. Why they do it that way, I don't know, but they do. If you descend to 3000 (or whatever altitude) right when they say, you can be in for a bad day.

So yeah, there's one way to operate in the US and another, more cautious, way to operate overseas. That could've be the frame of mind the DE in the original post was operating in.
 
Re: Maintain altitude until glide slope intercept or step do

Alchemy said:
I don't know if you've seen them but for some international destinations Jepp publishes a "minimum vector altitude" chart on something like a 10-1B page. It gives you the lowest altitudes that ATC is supposed to vector you to. In the US, yeah, you can generally trust the controllers. In Mexico, however, someitmes they give you a "descend to 3000 clearance cleared for the VOR/DME-2 approach" but what they really mean is "descend to 3000 AFTER you're established on the appropriate segement of the approach to go that low". As a result I always consulted the charted altitudes and made sure the clearance wasn't sending me below them. Why they do it that way, I don't know, but they do. If you descend to 3000 (or whatever altitude) right when they say, you can be in for a bad day.

So yeah, there's one way to operate in the US and another, more cautious, way to operate overseas. That could've be the frame of mind the DE in the original post was operating in.
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Yup, those MVA charts were a necessity going into Mexico. I've counted four instances of controllers down there clearing us below minimum IFR altitudes without even thinking twice. GPWS event waiting to happen (if you're lucky).

Actually, I got ribbed quite a bit when I told people most of my international experience was going into Mexico. They told me it wasn't "real" international flying. Well, I've been doing "real" international flying for a little while now and Mexico still takes the cake for me as the most hazardous.
 
Re: Maintain altitude until glide slope intercept or step do

I've flown into Mexico quite a bit, but I haven't flown into areas with mountanous terrain. I've dealt with some wacky clearances like the one I've described above with being cleared to an altitude below the glide slope intercept altitude to intercept the ILS .
 
Re: Maintain altitude until glide slope intercept or step do

Trip7 said:
Long range, short range? Are you talking about switching from white to green needles?
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A few days late, but yes.

Different aircraft use different colored needles for different things so saying white to green (CRJ) to an ERJ or Boeing guy might not make sense. Ground based = short range and sat (or inertial) = long range. And then try telling an Airbus guy anything about ground based nav and they will just roll their eyes at you.
 
Re: Maintain altitude until glide slope intercept or step do

dasleben said:
Actually, I got ribbed quite a bit when I told people most of my international experience was going into Mexico. They told me it wasn't "real" international flying. Well, I've been doing "real" international flying for a little while now and Mexico still takes the cake for me as the most hazardous.
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Maybe their perception are the "big 3" Mexican airports....MEX/GDL/MTY...Those from an ATC perspective offer the niceties of fairly good English, radar etc...The other 20 or so smaller airports we go to, not so much.
 
Re: Maintain altitude until glide slope intercept or step do

Baronman said:
Maybe their perception are the "big 3" Mexican airports....MEX/GDL/MTY...Those from an ATC perspective offer the niceties of fairly good English, radar etc...The other 20 or so smaller airports we go to, not so much.
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Precisely. Interior of Mexico is quite a bit different.
 
Re: Maintain altitude until glide slope intercept or step do

ClearedToThe said:
Your argument would hold if not every ILS freq at ATL has a PRM approach associated with it. If you can't bust an altitude while flying a PRM, you're not going to bust it flying a standard ILS approach to the same runway...
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I'm not making an "argument"; I'm just stating a fact.

But to ensure your position is clear, are you saying that when the FAA wrote that there were multiple altitude deviations there that they were just pulling our leg or what?
 
Re: Maintain altitude until glide slope intercept or step do

Guy said:
I'm not making an "argument"; I'm just stating a fact.

But to ensure your position is clear, are you saying that when the FAA wrote that there were multiple altitude deviations there that they were just pulling our leg or what?
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I was just making the observation that both of them (the FAA letter and the note on the PRM page) can not both be correct.

Maybe the altitude busts the FAA is talking about had nothing to do with riding the GS down to the runway, but instead were caused by something else.

Either way, "We're from the FAA and we're here to help!" :insane:
 
Re: Maintain altitude until glide slope intercept or step do

B767 said:
I may be stepping out of my bounds here...

If I recall, there are actually 2 "glide slopes" on an ILS. One is correct, and the other is much higher (altitude) signal and requires a steeper descent to the runway. Based on that, and me being me, I'd rather step down and intercept at the appropriate, i.e. published, intercept altitude. I worry that I might intercept the false glide slope from the higher altitude.
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Actually there can be many more than even 2 glideslopes, which is why there's a tiny number printed on your Jepp chart at the final minimum GS intercept point. (fly all the way up about 10 miles of any localizer and watch how many times the GS passes through!) It usually reads: GS-####, this is an MSL number for you to check that you are indeed on the correct glideslope..more than 75 feet off, (max altimeter error) and the correct baro on the dial, level off..etc...etc...etc..

I maintain my last altitude, above the minimum stated by ATC until on glideslope, then follow all the way down, one nice descent, not really passenger comfort, but for my workload...and when I was still with a regional, never had a captain or a fed poo poo me for it either.
 
Re: Maintain altitude until glide slope intercept or step do

This thread has been a great learning experience for ne, especially as an ATL based pilot. Ive always just intercepted the glideslope and relaxed. Based on this thread ive tried white needles/long nav, dive and drive, and simply just montering raw data gs descent. By far the least workload is raw data descent monitering. In the CrJ if you put the crossing restriction into the altitude alerter the 'banana bar' will show you if you will bust your crossing restriction.
 
Re: Maintain altitude until glide slope intercept or step do

B767 said:
I may be stepping out of my bounds here...

If I recall, there are actually 2 "glide slopes" on an ILS. One is correct, and the other is much higher (altitude) signal and requires a steeper descent to the runway. Based on that, and me being me, I'd rather step down and intercept at the appropriate, i.e. published, intercept altitude. I worry that I might intercept the false glide slope from the higher altitude.
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Are you talking side lobes, or two modulated signals?? loc and glide slope work on a depth of modulation of two reference sigs modulated at different hertz rates... Side lobes are what gives you false glide slopes and are totally unreliable, not set at a higher approach angle.

You always want to intercept the GS from below, on a published segment inside the service volume.
 
The ATL FSDO is aware of this, and will be adding more guidance soon. Until then operate as normal, and file an ASAP if necessary. There have been several ASAPs on this at ASA due to FAA investigations.

Stepping down while inbound on an ILS carries more risk than just staying on glideslope, so I'm hoping some relief for specific airports comes out.
 
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