Re: Bad example Jerry! (Greetings from the new guy.)

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Hello all,

By way of greeting, I’m a CSI (also CFI/CFII/MEI in airplanes and CFI/CFII in helicopters) at Air Orlando in Central Florida. I have lurked through the forums for some time but haven’t joined the public forums until just now. I am not a COPA member, although our flight school does maintain a COPA membership. Since that name is under our marketing director, Gary Hillyer, I will post under my own name, and only in the public forums for now. Anyway - hello! Good group ya’ll have here.

I wanted to interject my own comments with regards to the discussion between Scott Dennstaedt and Jerrold Seckler about glideslope intercept altitude and acceptable procedures for intercepting the glideslope.

I think there may be a small element of communication breakdown between Jerrold and Scott. Scott’s pretty much got it right when it comes to GSIA and the appropriate (mandatory) GSIA, but what has been completely neglected (unless maybe I missed it!) by both parties is the fact that ATC authorization is required to intercept the glideslope at ANY altitude other than that published on the IAP.

Scott has correctly noted that on some instrument approach procedures, glideslope intercept may occur at altitudes other than the GSIA. However, this requires ATC authorization. To independently choose to intercept the glideslope at any other altitude would be a pilot deviation from an ATC instruction.

In a message dated 6/10 Jerrold stated:

“In each case ATC will turn you on the localizer below the glideslope at that point and give you a minimum altitude until established, or a mandatory crossing altitude. You can hold that altitude until GS interception and fly it down.”

I disagree with this statement. First, there is absolutely no requirement for ATC to vector or route an aircraft onto the final segment of an approach at an altitude below GSIA. A review of the NACO terminal procedures will show a significant number of approaches which feature initial and intermediate segments at altitudes above the published GSIA. ATC’s MVA (minimum vectoring altitude) may also be above GSIA. The minimum altitude until established means exactly that - maintain the assigned altitude until established on the localizer. In fact, the exact verbiage ATC uses is, “Maintain XXXX until established on the localizer/final approach course.” Normally, no mention of glideslope intercept or GSIA is made. If no authorization is given by ATC for intercepting the glideslope at any aItitude other than that published on the IAP, the pilot must intercept the glideslope at that altitude.

Thus, if the aircraft becomes established at an altitude above glideslope intercept, it is incumbent upon the pilot to descend to the published (or assigned) GSIA prior to intercepting the glideslope. The reason for this, among others, is to avoid intercepting the glideslope from above (especially important when flying coupled approaches.)

The AIM provides some guidance on this topic in 1-1-9:

"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.

  1. Pilots must be alert when approaching the glidepath interception. False courses and reverse sensing will occur at angles considerably greater than the published path."

In other words, there’s no way for the pilot to know exactly how far out on the approach the glideslope signal may be used - all that the AIM tells us is that the glideslope is “normally usable” up to 10nm distance from the transmitter, and may be certified for an extended service volume at certain locations. So don’t count on the glideslope indication above GSIA being reliable, folks.

The subsequent advisory is also of interest. Clearly the angle at which the aircraft intercepts the glideslope is of importance; “False courses and reverse sensing will occur at angles considerably greater than the published path.” Intercept at level altitude - at your published or assigned glide slope intercept altitude.

Procedure turns and airline procedures have no real bearing on this discussion. We all follow the same rules. Keep in mind that the approaches the airlines fly are often Cat II or IIIa approaches - completely separate published procedures from what the majority of GA use.

Hope this input is regarded as helpful.

Best,

-Ryan

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In reply to:

First, there is absolutely no requirement for ATC to vector or route an aircraft onto the final segment of an approach at an altitude below GSIA.

Welcome Ryan.

You stated this correctly, but just let me add a bit of clarification here since this always tends to add a bit of confusion. ATC does have a requirement to vector you at an altitude “below the GS” but not necessarily below the GSIA.

From FAA Order 7110.65N:

5-9-1 Vectors to Final Approach Course
Except as provided in paragraph 7-4-2, Vectors For Visual Approach, vector arriving aircraft to intercept the final approach course:

a. At least 2 miles outside the approach gate unless one of the following exists:

	1. When the reported ceiling is at least 500 feet above the MVA/MIA and the visibility is at least 3 miles (report may be a PIREP if no weather is reported for the airport), aircraft may be vectored to intercept the final approach course closer than 2 miles outside the approach gate but no closer than the approach gate.

	2. If specifically requested by the pilot, aircraft may be vectored to intercept the final approach course inside the approach gate but no closer than the final approach fix.

b. For a precision approach, at an altitude not above the glideslope/glidepath or below the minimum glideslope intercept altitude specified on the approach procedure chart.

c. For a nonprecision approach, at an altitude which will allow descent in accordance with the published procedure.
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Ryan,
Thank you for the post.
I was going to quote the controller’s manual regarding vectoring altitudes for a precision approach but Scott beat me to it.
There is NO argument that if you are above the glideslope when cleared for the approach (an unusual situation) you should NOT try to capture the GS from that position. Rather you need to descend to the GSIA and then when you intercept the GS commence tracking it.
The initial question concerned an approach that you were being vectored for, wer turned on the LOC and told to maintain 1700 until established, cleared for the approach. The GSIA is 1300 feet. The question was can you maintain 1700 until GS interception or must you go farther below the GS to intercept it at 1300 feet? I maintain that assuming when you are established at 1700 and have a fly up indication on the GS there is NO regulation to prohibit you from maintaining 1700, flying into the GS and then following it down. I do not see how that violates any FAR or ATC instruction. I also do not see how it is unsafe. As a practical matter it is very common to be turned on a localizer a few miles from the marker at an altitude below the GS and be given a clearance that says something like "three from XYZ, maintain x thousand until established, cleared ILS runway xx approach.
The GSIA is defined at the minimum altitude you can intercept the GS. That implies you can intercept at a higher altitude.
Welcome to the forums. I really enjoyed your excellend first contribution.
By the way, Scott and I like to spar over these things for mutual amusement.

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In reply to:

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I disagree with this statement. First, there is absolutely no requirement for ATC to vector or route an aircraft onto the final segment of an approach at an altitude below GSIA. A review of the NACO terminal procedures will show a significant number of approaches which feature initial and intermediate segments at altitudes above the published GSIA. ATC’s MVA (minimum vectoring altitude) may also be above GSIA.

Ryan,

Just fly in and out of New York (EWR, LGA and JFK) for a few days and you will see that what you disagree with above happens all the time. Furthermore the MVA’s are not shown to pilots so in my opinion is if no concern to me. Since the FED’s are not going to give me that info I have no use for it.

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In reply to:

c. For a nonprecision approach, at an altitude which will allow descent in accordance with the published procedure.

This brings up somewhat of a question. I had to do the GPS 9 into the attached airport yesterday. Four miles out (from the IAF), I still hadn’t receive my clearance. I called ATC, received my clearance to cross EJIVU at or above 3000 ft. I couldn’t quite figure out the reason for this but complied none the less. Broke out a 2000’ msl.

Any ideas?

Mike
1-93843-8a7_ndb_or_gps_rwy_09.pdf (22.1 KB)

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Good reference Scott. Concur…

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Jerry,

Thanks for your reply.

In reply to:

I was going to quote the controller’s manual regarding vectoring altitudes for a precision approach but Scott beat me to it.

Yes, there is nothing in Scott’s reference to the 7110.65 that I disagree with.

In reply to:

There is NO argument that if you are above the glideslope when cleared for the approach (an unusual situation) you should NOT try to capture the GS from that position. Rather you need to descend to the GSIA and then when you intercept the GS commence tracking it.

Agreed on both counts (yes, it is unusual, and if it occurs, you should descend below the glideslope and interecept from below.)

In reply to:

The initial question concerned an approach that you were being vectored for, wer turned on the LOC and told to maintain 1700 until established, cleared for the approach. The GSIA is 1300 feet. The question was can you maintain 1700 until GS interception or must you go farther below the GS to intercept it at 1300 feet?

You maintain 1700 until established… “on the localizer” or “final approach course”, and then descend to 1300 feet, assuming you’re within 10nm (or whatever distance is depicted on the procedure) to intercept the glideslope. This is how the procedure is publshed and how it must be flown, unless instructed otherwise.

In reply to:

I maintain that assuming when you are established at 1700 and have a fly up indication on the GS there is NO regulation to prohibit you from maintaining 1700, flying into the GS and then following it down. I do not see how that violates any FAR or ATC instruction. I also do not see how it is unsafe.

As to whether or not it’s unsafe, it’s beyond my capabilities as a pilot flying a given approach, which I did not design, to know how or why the terps designers chose the glide slope intercept altitude on the plate. It’d simply be a guess.

Could one be violated for intercepting the glideslope at an altitude other than that authorized by the IAP or ATC? I doubt that would occur under normal circumstances, simply because ATC doesn’t have much of a reason to care or be concerned unless the aircraft is involved in an incident or accident. But it is definitely a deviation from an ATC instruction - if you choose to fly the procedure as you’ve described, you’re flying a self-modified approach.

In reply to:

As a practical matter it is very common to be turned on a localizer a few miles from the marker at an altitude below the GS and be given a clearance that says something like "three from XYZ, maintain x thousand until established, cleared ILS runway xx approach.
The GSIA is defined at the minimum altitude you can intercept the GS. That implies you can intercept at a higher altitude.

The only thing it implies is that ATC authorization may grant you the option to intercept the glideslope at a higher altitude; but this is not a choice which the pilot may make independently.

In reply to:

Welcome to the forums. I really enjoyed your excellend first contribution.
By the way, Scott and I like to spar over these things for mutual amusement.

Thank you, Jerry. I look forward to future discussions.

-Ryan

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Mike - I’ve had similar situations. I always figured they kept me a little high to keep me in radar contact when there was other IFR traffic involved. Some separation rule or something. Just speculating, but that might explain the “late” clearance, too.

Tom

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In reply to:

This brings up somewhat of a question. I had to do the GPS 9 into the attached airport yesterday. Four miles out (from the IAF), I still hadn’t receive my clearance. I called ATC, received my clearance to cross EJIVU at or above 3000 ft. I couldn’t quite figure out the reason for this but complied none the less. Broke out a 2000’ msl.
Any ideas?
Mike

Other traffic would be my #1 bet. #2 would be that the controller didn’t know or bother to look up the altitude for the GPS approach.

Do you know what the minimum vectoring altitude is in that sector?

Jerry

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Mike,
I can’t tell you why you didn’t get the approach clearance sooner but this is a typical clearance for a non precision approach. I also don’t know how good Greensboro Approach Radar is in that area.
The key to understanding your clearance is found in the MSA of 4100 feet. That tells me there is terrain in that area. The controller has a minimum altitude he can give you (if you are being vectored it is called the Minimum Vectoring Altitude). If you are not being vectored you must go to an IAF and comply with the altitude from there (for example 3300 feet from GSO VOR to DVZ). I presume you were in radar contact and the MVA was 3000 feet in your area.
Once you get to DVZ or EJIUV and go outbound you can begin your descent to the PT altitude. But you MUST be established on the approach to do that. The 3000 foot restriction is then simply a way to keep you at a safe altitude until you are able to descend on the charted approach.
If you were being VECTORED to the final approach course it would seem you were being kept higher than necessary since according to the profile you certainly could be lower than 3000 when crossing EJIUV (actually you could be at the MDA at that point if you were doing the full published approach). Traffic is probably not a consideration since at a non towered field like this only one IFR operation is allowed at any time.
Were you being vectored to final or doing the full approach?

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Michael,

My guess is that you got a bum approach clearance. I suspect the clearance should have been “cross DVZ at or above 3000” not EJIVU. 3000 was probably the MVA, but once you are established on the approach after DVZ you can descend down to 2,500.

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Jerry,

Thanks for the reply.

In reply to:

The 3000 foot restriction is then simply a way to keep you at a safe altitude until you are able to descend on the charted approach.

I suspect you are right on this. I was approaching from the east. There is a tower (1815’) in that direction. While I would normally expect to be able to start my decent to 2500’ after crossing DVZ, the controller may have been trying to keep me up until he was sure I was clear of the tower, but when I ask for my clearance I announced my GPS distance from the airport and should have been past this tower.

Another possibility, last Friday another controller at this same facility would come on the radio and correct or clarify an instruction, like the primary controller was in training.

This particular approach was changed not terribly long ago. EJIVU was added. Not sure why or for what purpose.

At any rate, it seems of no real matter. Just questioned why.

Mike

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Michael,
The fix EJIVU is a “sensor fix” that is inserted in an overlay approach. If you were flying the approach as an NDB (whatever that is - ask Scott) it has no meaning.
This is what Jeppesen says about a sensor fix:

Definition: A Sensor FAF is a final approach waypoint created and added to the database sequence of waypoints to support GPS navigation of a published, no FAF, non-precision approach. The Sensor FAF is included in Jeppesen’s NavData waypoint sequence and included in the plan and profile views of no FAF non-precision approach charts. In some cases, a step down fix, recognized by a charted database identifier, may serve as the Sensor FAF.

That said I must confess I don’t really know its operational significance. With this procedure you descend to the MDA and if you reach the MAP without seeing the airport you miss.

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Actually Scott we don’t disagree too much on this one.
I understand the use of the MSA but the MSA of 4100 feet means that there clearly are some obstructions in the area that will certainly impact the MVAs. I really didn’t know whether the approach was vectored or given as a direct to …
It may have been that the controller simply screwed up, but to know how badly one needs to know if the approach was by vector or whether it was via DVZ and the full approach. Either way however an altitude restriction was there to ensure obstacle clearance until established on a published segment of the approach.

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In reply to:

That said I must confess I don’t really know its operational significance.

Jerry,

The database needs to know when to kick into approach mode so a fix has to be chosen. Don’t be shy Jerry, you have a few NDB approaches under your belt than you probably want to admit to.

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Scott,
I understand the fix is there to tell the unit to go to the higher sensitivity but I don’t know why it needs to be charted and named.

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Hello William,

Thanks for your reply. What exactly is it that occurs all the time? Aircraft being vectored in at, below, or above GSIA? Of course, all three of those scenarios will occur on a regular basis. (?) I don’t think I insinuated anything to the contrary, but if it was interpreted that way, my apologies.

As I recall it was one of Wally Roberts’ passions to find a way to disseminate ATC MVA data to pilots - I remember a sample plot he ran on his terps.com site for public consumption for a time. The data is not available in a graphical format, but there’s nothing precluding a pilot from simply asking what the MVA might be at his present position. And that data is most certainly pertinent on many occasions. This is a question I ask when trying to determine if I can slide under the clouds and get a visual or contact approach, based on the weather reported at the field.

Thanks,

Ryan

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In reply to:

As I recall it was one of Wally Roberts’ passions to find a way to disseminate ATC MVA data to pilots - I remember a sample plot he ran on his terps.com site for public consumption for a time.

Concur, and I believe one of the reasons he’d like it published is he’s found a number of dangerous errors in it, and he believes public availability would create greater scrutiny. Terrain avoidance is job #1!

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Jerry:

quote] I maintain that assuming when you are established at 1700 and have a fly up indication on the GS there is NO regulation to prohibit you from maintaining 1700, flying into the GS and then following it down. I do not see how that violates any FAR or ATC instruction. I also do not see how it is unsafe.
[/quote]

Ryan:

In reply to:

As to whether or not it’s unsafe, it’s beyond my capabilities as a pilot flying a given approach, which I did not design, to know how or why the terps designers chose the glide slope intercept altitude on the plate. It’d simply be a guess.

Could one be violated for intercepting the glideslope at an altitude other than that authorized by the IAP or ATC? I doubt that would occur under normal circumstances, simply because ATC doesn’t have much of a reason to care or be concerned unless the aircraft is involved in an incident or accident. But it is definitely a deviation from an ATC instruction - if you choose to fly the procedure as you’ve described, you’re flying a self-modified approach.

Jerry, Ryan…

Could one descend slowly - e.g. 100 fpm - once established on the localizer, thereby complying with the “descend” requirement without deviating from the ATC instruction, but remaining likely to intercept the glideslope early enough to intercept it from below and then increase descent rate and follow the GS?

[Just re-read the preceding sentence - hope you understand it - I do, but perhaps only because it came from me!]

  • Mike.