LOC/DME Approach, Surprised to see glide slope

carrollm

carrollm

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Flying into the AOPA fly-in this weekend they were using the Salinas Airport LOC/DME RNWY 31 approach. This same runway has a separate published ILS approach. I haven't flown a localizer approach in a while and was surprised to see my GNS530W/G600 display a glide slope. I also noticed there where no step down altitudes on the approach chart profile, rather a constant descent angle was depicted. Am I remembering incorrectly, I thought the non-precision localizer approached normally, or use use to have, step-down approaches. Is this only the case when there is not an ILS for the same runway or am I just confused (entirely possible).
 
Let's start by reviewing the two charts involved:

LOC/DME RWY 31
ILS RWY 31

Note that it's the same localizer used on both approaches. So, if you have a GS receiver, you'll get the GS indications regardless of which piece of paper you're using. The big difference is that if you don't have a DME, you can still fly the ILS approach as long as you have an ADF and a working GS receiver. And unless you're looking at the wrong approach chart (i.e., the ILS 31 instead of the LOC/DME 31), there most definitely are step-down altitudes on the LOC/DME RWY 31 approach.
 
Important correction:

The LOM at SNS is NOTAMed permanently inop, so you MUST have DME (or GPS) to fly either approach. ADF will not cut it for the ILS.
!SNS 02/011 SNS NAV ILS RWY 31 CHUALAR LOM DECOMSSIONED 1502130842-PERM
Click to expand...

Also, at least some Garmins (certainly 650s) will show an "advisory" GS with the CDI in GPS mode, so if you're seeing a GS on a LOC-only approach (like at Watsonville), check the bust (CDI) button and set it to VLOC like it should be.
 
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carrollm said:
Flying into the AOPA fly-in this weekend they were using the Salinas Airport LOC/DME RNWY 31 approach. This same runway has a separate published ILS approach. I haven't flown a localizer approach in a while and was surprised to see my GNS530W/G600 display a glide slope. I also noticed there where no step down altitudes on the approach chart profile, rather a constant descent angle was depicted. Am I remembering incorrectly, I thought the non-precision localizer approached normally, or use use to have, step-down approaches. Is this only the case when there is not an ILS for the same runway or am I just confused (entirely possible).
Click to expand...

If both the LOC and ILS procedures are using the same localizer frequency, why would you expect the the glide path not to show up just because you pulled up the LOC procedure on your chart viewer?

If there were no step-downs on the chart, are you sure you pulled up the LOC procedure?
 
There are definitely step-downs on the LOC/DME approach at SNS. I flew it a few weeks ago.

Any chance this might be confusion between the Jepp and NACO profile views? Jepp explicitly shows the step downs. NACO just shows a line.
 
MAKG1 said:
Important correction:

The LOM at SNS is NOTAMed permanently inop, so you MUST have DME (or GPS) to fly either approach. ADF will not cut it for the ILS.
Click to expand...
If that is true, there should also be an FDC NOTAM modifying the ILS 31 approach, and I'm not finding one And you can certainly fly the ILS 31 without an ADF if you get vectors to final, so the modification should be to change "ADF OR DME REQUIRED" to "DME OR RADAR REQUIRED".
 
MAKG1 said:
There are definitely step-downs on the LOC/DME approach at SNS. I flew it a few weeks ago.

Any chance this might be confusion between the Jepp and NACO profile views? Jepp explicitly shows the step downs. NACO just shows a line.
Click to expand...

The FAA chart isn't just a line. There is an underscored altitude at each step-down fix.
 
MAKG1 said:
Yes. As with the Jepp charts. They both have the altitudes published.

I was referring to the plotted shape of the profile.
Click to expand...

"Chart Reading 101" so to speak. :)
 
I believe the OP's question has been adequately addressed. The big question here seems to be why there is no FDC Notam re: the permanent closure of the OM ? Or is MAKG's input in that regard not correct ? If it is correct, why hasn't the FAA gotten around to the Notam ?
 
Edgefly said:
I believe the OP's question has been adequately addressed. The big question here seems to be why there is no FDC Notam re: the permanent closure of the OM ? Or is MAKG's input in that regard not correct ? If it is correct, why hasn't the FAA gotten around to the Notam ?
Click to expand...

02/011 - NAV ILS RWY 31 CHUALAR LOM DECOMSSIONED. 13 FEB 08:42 2015 UNTIL PERM. CREATED:
13 FEB 08:50 2015
 
Straying from the original question here but still on one of the plates. On the ILS RWY 31, the Glidepath Altitude at the SNS 12.1 DME seems wrong. Like they added DA to it.
 
luvflyin said:
Straying from the original question here but still on one of the plates. On the ILS RWY 31, the Glidepath Altitude at the SNS 12.1 DME seems wrong. Like they added DA to it.
Click to expand...

Looks correct, or within reason, to me. Can you show us why you don't think it's correct?
(Don't forget the earth's curvature, if you are doing the math.)
 
RotorDude said:
Looks correct, or within reason, to me. Can you show us why you don't think it's correct?
(Don't forget the earth's curvature, if you are doing the math.)
Click to expand...

Quite a bit of curvature in that distance.
 
My calculation for the GS height at that point is within a foot of the charted value, but I am using a spreadsheet with the TERPS equation. The simple calculation at 300 feet per NM yields 3651. A better estimate using 318 feet/NM the calculation would be 3861.6. Adding a rough estimate of the curvature of the earth of 125 feet is also within a foot. My estimate of the curvature is to multiply the distance times the distance-1, so 11.7 X 10.7 = 125.18 feet.
 
John Collins said:
My calculation for the GS height at that point is within a foot of the charted value, but I am using a spreadsheet with the TERPS equation. The simple calculation at 300 feet per NM yields 3651. A better estimate using 318 feet/NM the calculation would be 3861.6. Adding a rough estimate of the curvature of the earth of 125 feet is also within a foot. My estimate of the curvature is to multiply the distance times the distance-1, so 11.7 X 10.7 = 125.18 feet.
Click to expand...

As I noted above, I can reproduce the published number to the foot.
Here it is (using python):
11.7 * math.tan((3/180.)*3.14159265358) * 6076.12 + curv(11.7)*6076.12 + 82 + 59
3987.4588401890787

curv is defined as:
def curv(r):
... R = 3443.89849
... return r/math.sin(math.atan(r/R)) - R

IOW, my assumption was a perfect sphere of 3443.89849 nm, and standard trig then yields the published number at 11.7 nm.
 
aterpster said:
02/011 - NAV ILS RWY 31 CHUALAR LOM DECOMSSIONED. 13 FEB 08:42 2015 UNTIL PERM. CREATED:
13 FEB 08:50 2015
Click to expand...
That's a NOTAM-D advising of the LOM decommissioning, not an FDC NOTAM modifying the ILS 31 procedure.
 
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Ron Levy said:
That's a NOTAM-D advising of the LOC decommissioning, not an FDC NOTAM modifying the ILS 31 procedure.
Click to expand...

The LOC works fine. The LOM has been decommissioned.

While I agree there "should" be an FDC NOTAM, it's pretty clear that you can't identify the FAF if all you have is an ADF and a localizer receiver.
 
With regard to the step down versus constant glideslope line on the chart profile view, I was using Jepp charts last time I flew a localizer approach, so the constant glide path depicted on the Govt chart displayed on my Ipad Saturday probably explains why that was different. (Yes, both have altitudes listed at each DME fix.) I was tuned to VLOC and again, don't remember a glide slope when doing other localizer approaches that also have as separate ILS approach, such as a few years back at Oxnard when the localizer and ILS approaches were different approaches with different plates. Obviously need to include more localizer approaches in my air work. Thanks for all the great information.
 
MAKG1 said:
The LOC works fine. The LOM has been decommissioned.
Click to expand...
Typo fixed. Thanks.

While I agree there "should" be an FDC NOTAM, it's pretty clear that you can't identify the FAF if all you have is an ADF and a localizer receiver.
Click to expand...
The FAF on the ILS 31 approach (GS intercept) can be identified just fine without either ADF or DME if you get vectors to final. The ADF or DME is needed only for full procedure entry. So, there really should be an FDC NOTAM making a change to the procedure. Therefore, this is worth reporting to AeroNav.
 
carrollm said:
With regard to the step down versus constant glideslope line on the chart profile view, I was using Jepp charts last time I flew a localizer approach, so the constant glide path depicted on the Govt chart displayed on my Ipad Saturday probably explains why that was different. (Yes, both have altitudes listed at each DME fix.) I was tuned to VLOC and again, don't remember a glide slope when doing other localizer approaches that also have as separate ILS approach, such as a few years back at Oxnard when the localizer and ILS approaches were different approaches with different plates. Obviously need to include more localizer approaches in my air work. Thanks for all the great information.
Click to expand...

The GS might have been there but maybe you were below it for most of the approach and didn't notice it? It should show up as long as it is in service but you'd only notice it on the CDI while you're on or near the GS. IOW once you dive down to a step down fix you might be below the GS such that it's off scale.
 
Ron Levy said:
That's a NOTAM-D advising of the LOM decommissioning, not an FDC NOTAM modifying the ILS 31 procedure.
Click to expand...

True enough. But, you know how it works with those folks in OKC. :)

At least the D NOTAM provides the essential information to the alert pilot.
 
RotorDude said:
Looks correct, or within reason, to me. Can you show us why you don't think it's correct?
(Don't forget the earth's curvature, if you are doing the math.)
Click to expand...

I was doing the math. 11.7 * 319 + 82 = 3814. Did it again with 11.9 figuring the 11.7 is the RW end and the Glideslope intersects the RW farther down and still came up short. The curvature of the Earth never crossed my mind. I had no idea it could be that much in that short a distance.
 
luvflyin said:
I was doing the math. 11.7 * 319 + 82 = 3814. Did it again with 11.9 figuring the 11.7 is the RW end and the Glideslope intersects the RW farther down and still came up short. The curvature of the Earth never crossed my mind. I had no idea it could be that much in that short a distance.
Click to expand...

A quick way of estimating the curvature of the earth on a GS that is a straight line in space is to multiply the distance from the runway in NM times the distance minus 1. So 11.7 X 10.7 = 125.19 feet. This works for an ILS GS or an LPV GS. For an LNAV/VNAV the GS accounts for the curvature of the earth because the GS is not a straight line in space.
 
John Collins said:
A quick way of estimating the curvature of the earth on a GS that is a straight line in space is to multiply the distance from the runway in NM times the distance minus 1. So 11.7 X 10.7 = 125.19 feet. This works for an ILS GS or an LPV GS. For an LNAV/VNAV the GS accounts for the curvature of the earth because the GS is not a straight line in space.
Click to expand...
Thanks for that info John, I did not know that!
 
John Collins said:
A quick way of estimating the curvature of the earth on a GS that is a straight line in space is to multiply the distance from the runway in NM times the distance minus 1. So 11.7 X 10.7 = 125.19 feet. This works for an ILS GS or an LPV GS. For an LNAV/VNAV the GS accounts for the curvature of the earth because the GS is not a straight line in space.
Click to expand...

Thanks for the info. What exactly is the feet per mile they use for a 3 degree Glideslope. I've seen everything from 300 to 320. I started out with a degree is one mile 60 miles out and worked it back in and got 319.
 
luvflyin said:
Thanks for the info. What exactly is the feet per mile they use for a 3 degree Glideslope. I've seen everything from 300 to 320. I started out with a degree is one mile 60 miles out and worked it back in and got 319.
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Sometimes called the "Pennsylvania approximation", after the state legislature that decreed pi = 3, exactly.

At least, so the story goes. B)
 
Right, last I checked the nautical mile was defined to be exactly 1852 meters.
 
aterpster said:
Picking at nits: The FAA nautical mile was 6076.1155 for many years. Recently, it became 6076.11548.

Not that it makes any difference for this purpose.
Click to expand...

FWIW, according to WP, a nautical mile = 1852 meters, or 2,315,000/381 feet, both exactly.
The latter translates to 6076.115485564304 feet.
 
aterpster said:
Apparently for TERPs measurements and calculation purposes 6076.11548 does the job.
Click to expand...

Well, the difference between the scientifically correct value and the TERPs approved one is: (6076.115485564304 - 6076.11548)*12 = 67 micro-inches = 1.7 microns, which is about a tenth the thickness of a human hair.
Is this where "splitting hairs" came from?
 
John Collins said:
6076.1 X Tan (3) = 318.435.
Click to expand...

How do I do that on a calculator? I'm trying all kinds of combinations with that Tan button and nothing comes out making sense. It's the calculator on a IPhone 5c that when you turn it sideways it goes scientific.
 
On a non-HP calculator you might have to do 6076.1*(tan(3)). If it has a radians mode be sure it's NOT in that mode, but in degrees mode. I can't try this out on my iPhone since it doesn't seem to go scientific when held sideways.
 
luvflyin said:
How do I do that on a calculator? I'm trying all kinds of combinations with that Tan button and nothing comes out making sense. It's the calculator on a IPhone 5c that when you turn it sideways it goes scientific.
Click to expand...

On my iPhone, you have to enter the angle 3 and then tap Tan. Then X and 6076 then equal.
 
luvflyin said:
How do I do that on a calculator? I'm trying all kinds of combinations with that Tan button and nothing comes out making sense. It's the calculator on a IPhone 5c that when you turn it sideways it goes scientific.
Click to expand...

I have Calc Pro on my 6 Plus. It works fine provided I switch it to the scientific mode. I normally use an HP 32S, which is easier for me.
 
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