Intercepting ILS final approach course, do I have to descend right away?

[rookie1255]

Say I'm turning to intercept the final approach course that has me descend from 3000 to 2000 where the GS intercept is. Is it recommended/required that I descend down to 2000 "chop and drop" style like a non precision approach, or can I just hold 3000 until the GS comes in and then follow it down? Would choosing one method or another cause me to fail an instrument checkride?

 

[Cricket1]

Hold 3,000 until the glideslope comes in, then follow it down. Easy peasy. Obviously at 3K the GS is going to be further out from the outer marker than it will at 2,000, so if you are already past it at 3K, and do nothing you won't ever intercept it.

 

[asicer]

Whatever you do, make sure the altimeter agrees when you are at the GS intercept point or you could be in for a really bad day. And be aware of the presence of false glideslopes and how they occur.

 

[Palmpilot]

One instructor that I started an IPC with claimed that the FAA "wanted" pilots to intercept the glideslope at the charted intercept altitude. Whether there's anything in print from the FAA to support that, I don't know. Previous instructors I had flown with recommended not descending until intercepting the glideslope.

One caveat, however, is that if you do that before the last stepdown prior to the charted glideslope intercept, it can cause you to bust stepdown altitudes, depending on the barometric pressure. Some airline pilots reportedly got busted for that on approach to LAX. [Edit: Based on later posts, this depends on temperature, not barometric pressure.]

 

[bobmrg]

My practice was to hold altitude until the glideslope came down.Never had ATC question it. If the profile showed a stepdown, though, I followed it as charted. You never know why procedures designers do things the way they do, but they must have a reason, and I would rather not find out why the hard way.

Bob

 

[Let'sgoflying!]

ATC will say, “N1234 4 miles from ABCDE; maintain X000’ until established, cleared approach rwy XY.”

 

[AggieMike88]

ATC will say, “N1234 4 miles from ABCDE; maintain X000’ until established, cleared approach rwy XY.”

I have had this as well as “... at or above xx00 until established....”

 

[Bill]

ATC will say, “N1234 4 miles from ABCDE; maintain X000’ until established, cleared approach rwy XY.”

Exactly, they always give me an altitude with the vector to join the localizer.

 

[PaulS]

I have had this as well as “... at or above xx00 until established....”

Just want to be clear, "at or above until established" refers to intercepting the localizer in this case or the final approach course for gps. It's not talking about intercepting the glide slope, once you are on the localizer you can descend as charted.

I would be nervous intercepting a glide slope 1,000 feet above if a stepdown is there. For rnav with vertical guidance, I generally will just wait to intercept then make sure I don't bust any stepdowns if it's vertical guidance versus lpv.

 

[RussR]

Almost every altitude on every procedure is an "at or above altitude". The cases where there is an "at" altitude or even a "below" altitude exist, and require special attention, but for most procedures at most airports, "at or above" is the rule. If ATC needs something different they will have to tell you.

If they clear you to "maintain 4000 until established", then yes, you have to be at 4000, not above 4000, but once you're established, then all of the subsequent altitudes are "at or above". So, stay at 4000 if you like, or descend to the published altitude, or something in between.

Altitudes at fixes on the intermediate segment (between the IF and the FAF) "should" all be below glideslope, that's the TERPS standard. There are a few exceptions, and sometimes the errors in barometric altimetry will cause you grief, and you do need to pay attention, but in general that's true.

 

[Groundpounder]

You are 1 mile from VINGS at 2000, and you’re cleared for the approach. Tell me what you’ll do

 

[jordane93]

You are 1 mile from VINGS at 2000, and you’re cleared for the approach. Tell me what you’ll do

Never flown it but I hear if you follow the GS down from VINGS you’ll bust the mandatory altitude at DANDY

 

[Groundpounder]

Never flown it but I hear if you follow the GS down from VINGS you’ll bust the mandatory altitude at DANDY

Did you look at the chart?

 

[jordane93]

Did you look at the chart?

Yes

 

[Groundpounder]

Sorry didn't mean to be snarky. There is a mandatory altitude at DANDY. If you you stay at 2000 and intercept the GS, you'll be high at the mandatory, and possibly cause issues with EWR traffic.

There is an approach into LAX that has the same issue, but not sure which one it is.

So anyway, to the OP, it's a bad habit to get into, if you're not careful, it will bite you someday.

 

[PaulS]

Fly to vings at 2000 since you are already there, intercept the localizer, descend to 1,500, make sure you cross Dandy at 1500, then I would descend to 1,300 and capture the GS.

 

[luvflyin]

Fly to vings at 2000 since you are already there, intercept the localizer, descend to 1,500, make sure you cross Dandy at 1500, then I would descend to 1,300 and capture the GS.

Why not just intercept the Glideslope at 1500? Just 2.2 miles and 200 feet seems like a small space to do a 'dive and drive.'

 

[PaulS]

Why not just intercept the Glideslope at 1500? Just 2.2 miles and 200 feet seems like a small space to do a 'dive and drive.'

Rnav, no problem, ils, I'd rather be at the altitude they want. At 500 fpm 200 feet should take about 30 seconds, or about a mile for what I'm flying. Shouldn't be a problem. Still refining this stuff though, so what would probably happen is as I'm waiting to get ready to dive the 200 feet, I'd intercept.

 

[Palmpilot]

Why not just intercept the Glideslope at 1500? Just 2.2 miles and 200 feet seems like a small space to do a 'dive and drive.'

Agreed. The way I've heard it, once you're inside the last stepdown, you're free to maintain altitude until you intercept the glideslope.

 

[Palmpilot]

Rnav, no problem, ils, I'd rather be at the altitude they want. At 500 fpm 200 feet should take about 30 seconds, or about a mile for what I'm flying. Shouldn't be a problem. Still refining this stuff though, so what would probably happen is as I'm waiting to get ready to dive the 200 feet, I'd intercept.

The requirement as I understand it is to be at the glideslope intercept altitude by the time you reach the glideslope-intercept point. The rate of descent used to get to that altitude is up to the pilot. Why not just follow the glideslope down to that altitude? If you're at or near the previous stepdown altitude when you reach the last stepdown point, have you seen any published approaches where that would put you high enough to be in danger of intercepting a false glideslope?

 

[hindsight2020]

Reads the TEB plate, laughs in Category E.

 

[PaulS]

The requirement as I understand it is to be at the glideslope intercept altitude by the time you reach the glideslope-intercept point. The rate of descent used to get to that altitude is up to the pilot. Why not just follow the glideslope down to that altitude? If you're at or near the previous stepdown altitude when you reach the last stepdown point, have you seen any published approaches where that would put you high enough to be in danger of intercepting a false glideslope?

Actually no, I haven't, nor have a figured out how high I'd have to be to have a potential problem. So because I haven't really thought about it other than to know there can be a problem, I pretty much just fly the profile. But that's the extent of it. So if you are comfortable with intercepting above the final step down, I don't see any problem with doing that.

 

[smv]

The requirement as I understand it is to be at the glideslope intercept altitude by the time you reach the glideslope-intercept point. The rate of descent used to get to that altitude is up to the pilot. Why not just follow the glideslope down to that altitude? If you're at or near the previous stepdown altitude when you reach the last stepdown point, have you seen any published approaches where that would put you high enough to be in danger of intercepting a false glideslope?

Actually no, I haven't, nor have a figured out how high I'd have to be to have a potential problem. So because I haven't really thought about it other than to know there can be a problem, I pretty much just fly the profile. But that's the extent of it. So if you are comfortable with intercepting above the final step down, I don't see any problem with doing that.

Took a student on a quasi-ILS approach (very early in his training and I had him mostly just practicing using the localizer for LNAV). I kept him at about 4000AGL as we honed in on the localizer and flew right through the GS. Watching the ILS come and go several times after that transition was very enlightening. The last time we were "On Slope" with the GS needle centered there would have been no way to make a descent and still touch tarmac. We were nearly to the approach end of the runway.

Although I have never attempted to capture a GS from above, it sure made a believer out of me of ensuring I always capture from below.

 

[Palmpilot]

Actually no, I haven't, nor have a figured out how high I'd have to be to have a potential problem. So because I haven't really thought about it other than to know there can be a problem, I pretty much just fly the profile. But that's the extent of it. So if you are comfortable with intercepting above the final step down, I don't see any problem with doing that.

The first false null of the glideslope occurs at twice the angle of the true glideslope, or six degrees, but that has reverse sensing and will show a flag, according to this Web page:

https://encyclopedia2.thefreedictionary.com/false+glide-slope

Taking the example of the TEB ILS linked above, by my calculations that null would occur at about 4000 feet at DANDY, which is 2500 feet above the mandatory altitude at that fix. The first "usable" false glideslope, at six degrees, would be at about 6000 feet at DANDY. Even if there were not a mandatory altitude at DANDY, I'm not talking about crossing the last stepdown significantly above the altitude depicted prior to that stepdown, and I would be surprised to see an ILS where the minimum altitude before the last stepdown was high enough for intercepting a false glideslope to be a possibility. Even if there were such an approach, it seems to me that the flag at the six-degree null together with the reverse sensing, or having to use three times the normal descent rate on the nine-degree false glideslope, together with being at two or three times the specified height at the LOM, would be enough to alert the pilot to the fact that something was seriously wrong in either case.

 

[luvflyin]

Almost every altitude on every procedure is an "at or above altitude". The cases where there is an "at" altitude or even a "below" altitude exist, and require special attention, but for most procedures at most airports, "at or above" is the rule. If ATC needs something different they will have to tell you.

If they clear you to "maintain 4000 until established", then yes, you have to be at 4000, not above 4000, but once you're established, then all of the subsequent altitudes are "at or above". So, stay at 4000 if you like, or descend to the published altitude, or something in between.

Altitudes at fixes on the intermediate segment (between the IF and the FAF) "should" all be below glideslope, that's the TERPS standard. There are a few exceptions, and sometimes the errors in barometric altimetry will cause you grief, and you do need to pay attention, but in general that's true.

Yeah. But not so sure you really have to be at 4000 in your example. If you were at a higher altitude when ATC sprung the “maintain 4000 until established” and it required an excessive, maybe unsafe, rate of descent to do so it would not be good. This could happen if they held you at a higher altitude on the ‘base’ vector and sprung it on you just a few miles from the Final Approach Course with the ‘dogleg turn’ and Approach Clearance. When I was working, in this situation where the plane needed to be held high for traffic, but also needed to start down when the Clearance was given I would say “descend now, join the Localizer at or above...” If put in this situation by a controller I might recommend something like “out of five for four thousand, I’ll do my best to be there by intercept” in your read back.

 

[luvflyin]

Rnav, no problem, ils, I'd rather be at the altitude they want. At 500 fpm 200 feet should take about 30 seconds, or about a mile for what I'm flying. Shouldn't be a problem. Still refining this stuff though, so what would probably happen is as I'm waiting to get ready to dive the 200 feet, I'd intercept.

Yeah. It kinda boils down to how you ‘arrived’ at DANDY. It’s likely you would be level at 1500 when you did. If so, staying there and joining the Glideslope is the logical thing to do. No extra series of power and configuration changes while ‘diving and driving’ down to 1300. If you are able to cross DANDY at exactly 1500 while in a constant descent because you are are really good or your RNAV ‘gadgets’ allow you to, then it’s a matter of what that ‘angle of descent’ was during your descent to DANDY. If steeper than 3 degrees, you’re going to have to ‘arrest’ that angle of descent until intercepting the Glideslope. If shallower, holding that angle until intercepting is the easy way to go.

 

[midlifeflyer]

Actually no, I haven't, nor have a figured out how high I'd have to be to have a potential problem. So because I haven't really thought about it other than to know there can be a problem, I pretty much just fly the profile. But that's the extent of it. So if you are comfortable with intercepting above the final step down, I don't see any problem with doing that.

I hate angular math, so... The simplest rule of thumb is twice the AGL height. Using Ft Lauderdale as an example (because it is pretty much at sea level), you would have to cross the PFAF at 4000" to get a false glideslope. The further back, the higher, but so far, I haven't seen any lead-in altitude even close to twice the height of the PFAF.

Actually, it took me a while to change the habit of diving unnecessarily to the intercept altitude. Did it on GPS APV approaches too. Old habits die hard and produce some discomfort (which can be a very good thing too) even if one understands intellectually.

 

[Kenny Phillips]

You are 1 mile from VINGS at 2000, and you’re cleared for the approach. Tell me what you’ll do

Set the A/P for the approach and cross my arms.

 

[PaulS]

Set the A/P for the approach and cross my arms.

don't forget the VNAV button.

 

[kayoh190]

Set the A/P for the approach and cross my arms.

That's Groundpounder's point - if you have your A/P follow the ILS you'll bust the DANDY restriction.

 

[PaulS]

That's Groundpounder's point - if you have your A/P follow the ILS you'll bust the DANDY restriction.

Some autopilots are smarter than others, but you are correct, they all need to be watched.

 

[Sluggo63]

Sorry didn't mean to be snarky. There is a mandatory altitude at DANDY. If you you stay at 2000 and intercept the GS, you'll be high at the mandatory, and possibly cause issues with EWR traffic.

There is an approach into LAX that has the same issue, but not sure which one it is.

So anyway, to the OP, it's a bad habit to get into, if you're not careful, it will bite you someday.

It's a few of them, but here's an example for 25R.


If you intercept the LOC outside of GAATE and decide to capture the GS and ride it down, you'll bust the altitudes at GAATE and HUNDA.

 

[kayoh190]

Some autopilots are smarter than others, but you are correct, they all need to be watched.

I'd argue that autopilots are only as smart as the guidance they're working from. That's why it's important to actually look at the approach and use (or not use!) the automation accordingly. The TEB example is a common way to end up violated even in the most advanced flight decks. LAX 25L/24R is the common example for us airline types.

 

[Clip4]

Say I'm turning to intercept the final approach course that has me descend from 3000 to 2000 where the GS intercept is. Is it recommended/required that I descend down to 2000 "chop and drop" style like a non precision approach, or can I just hold 3000 until the GS comes in and then follow it down? Would choosing one method or another cause me to fail an instrument checkride?

From the instrument ACS,

Precision Approach

Maintain altitude ±100 feet, selected heading ±10°, airspeed ±10 knots, and accurately track radials, courses, and bearings, prior to beginning the final approach segment.

Adjust the published DA/DH and visibility criteria for the aircraft approach category, as appropriate, to account for NOTAMs, Inoperative airplane or navigation equipment, or inoperative visual aids associated with the landing environment.

Establish a predetermined rate of descent at the point where vertical guidance begins, which approximates that required for the airplane to follow the vertical guidance.

Maintain a stabilized final approach from the Final Approach Fix (FAF) to DA/DH allowing no more than 3⁄4-scale deflection of either the vertical or lateral guidance indications and maintain the desired airspeed ±10 knots.

Those that want to argue that means hold 3000 until intercept have at it.

 

[Clip4]

It's a few of them, but here's an example for 25R.
View attachment 86801

If you intercept the LOC outside of GAATE and decide to capture the GS and ride it down, you'll bust the altitudes at GAATE and HUNDA.

not to mention an LOC has 18 nm service volume.

 

[Sluggo63]

From the instrument ACS,

Precision Approach

Maintain altitude ±100 feet, selected heading ±10°, airspeed ±10 knots, and accurately track radials, courses, and bearings, prior to beginning the final approach segment.

Adjust the published DA/DH and visibility criteria for the aircraft approach category, as appropriate, to account for NOTAMs, Inoperative airplane or navigation equipment, or inoperative visual aids associated with the landing environment.

Establish a predetermined rate of descent at the point where vertical guidance begins, which approximates that required for the airplane to follow the vertical guidance.

Maintain a stabilized final approach from the Final Approach Fix (FAF) to DA/DH allowing no more than 3⁄4-scale deflection of either the vertical or lateral guidance indications and maintain the desired airspeed ±10 knots.

Those that want to argue that means hold 3000 until intercept have at it.

I don't see anything above that would prohibit staying at 3000' and intercepting the glidepath. How are you interpreting it where you think that you have to descend quickly to the FAF altitude to capture the glidepath?

 

[Sluggo63]

not to mention an LOC has 18 nm service volume.

It does, with some caveats. If ATC tells you to intercept the localizer and you're outside of the 18 NM service volume (and you're in radar contact), it is assumed that they are watching you and will give you any course corrections. The same goes if you request to follow the LOC and they approve it. They are responsible for you and letting you know if you stray significantly from the path.

In the LAX example, when the controller says "maintain at or above 5000 to GAATE, cleared the ILS runway 25R," you're good to follow the LOC even though you're outside the 18 NM service volume.

 

[aterpster]

There is an approach into LAX that has the same issue, but not sure which one it is.

It was all four ILS IAPs from the east 25L/R and 24L/R. On hot summer days following the GS out in the Ontario area resulted in more than a few altitude busts with Ontario traffic below being worked by a different sector of SoCal Approach Control. The step-down fixes were redesigned to abate the issue. None the less, prior to the official GP intercept point (lightning bolt on FAA charts) the step-down fixes govern minimum altitudes, not the GS. The airlines have become smarter about this at LAX by using Baro-VNAV outside the PFAF. The Baro-VNAV path "floats" with temperature, assuring compliance with the step-down fixes on hot days.

 

[Palmpilot]

It's a few of them, but here's an example for 25R.
View attachment 86801

If you intercept the LOC outside of GAATE and decide to capture the GS and ride it down, you'll bust the altitudes at GAATE and HUNDA.

I'm not seeing those fixes on the 25R chart. That looks like it's from the 25L chart.

 

[Palmpilot]

From the instrument ACS,

Precision Approach

Maintain altitude ±100 feet, selected heading ±10°, airspeed ±10 knots, and accurately track radials, courses, and bearings, prior to beginning the final approach segment.

One thing I've never understood is why +/-100 feet would apply to an altitude that is depicted as a minimum altitude on government charts. Shouldn't it be +100/-0?

...Those that want to argue that means hold 3000 until intercept have at it.

Has anyone ever been busted for doing that after the final stepdown fix?