Same airport - different GPS Approach types

WannFly

WannFly

Final Approach
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Priyo
i am starting my IR reading for the third time now... so pls bare with me.

I am trying to understand the logic behind having having different approaches on he same airport. Let me try to explain:

RNY 13 only has LNAV

upload_2020-4-19_14-9-29.png

RNY 31 has LPV. LNAV/VNAV, LNAV

upload_2020-4-19_14-10-13.png

trying to understand why LPV is not available on RNY 13

convenience? cost? obstruction? whats the logic?
 
There are many reasons. @asicer provided one, which is obstacle environment - sometime obstacles on one side of the airport just don't allow the vertically-guided approach procedures.

Another common cause is the type of (or existence of) an obstacle survey to the runway. A detailed obstacle survey costs money, so often airports (especially smaller ones) will only have a survey conducted to their primary runway. Without a survey, a vertically-guided approach cannot be developed (even if there are no real obstacles, there is no "proof" that there aren't, so it's assumed that there are), but a non-vertically guided approach can be. You see this all the time at airports where there is a large, main runway, and then a smaller "GA runway". The main runway will have LPV or even an ILS, but the smaller runway will only have LNAV.

Or, sometimes it's just that nobody at the airport has asked for an LPV approach to be developed to the other runway.

For specific airports, the best way to find out is to email the FAA at the link at the bottom of this web page:
https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/
 
Another reason that is not immediately obvious is that there is an obstacle in the missed approach path. We tend to look at the approach path and airport vicinity for clues without realizing that the something several miles away is giving the approach designer fits. When you see more than one GPS approach to the same runway with different minima, compare the missed approach procedures.

Bob Gardner
 
RW 13 indicates a 40 foot threshhold crossing height. (TCH) Must be something big near the RW 13 threshhold.
 
bobmrg said:
When you see more than one GPS approach to the same runway with different minima, compare the missed approach procedures.
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:yeahthat: Sometimes a 'RNAV (GPS) Z RWY nn' approach will say "Missed approach requires climb of xxx feet per NM to yyyy MSL. If unable to comply with climb gradiant use RNAV (GPS) Y RWY nn."

Other times, it will be because the Z approach says "authorization required" at the bottom.
 
And cost can be a factor. Each approach needs surveys and preparation. Sometimes, they don't even start on an approach to EACH runway.
Sometimes there are multiple approaches to the same runway.
 
bobmrg said:
Another reason that is not immediately obvious is that there is an obstacle in the missed approach path. We tend to look at the approach path and airport vicinity for clues without realizing that the something several miles away is giving the approach designer fits. When you see more than one GPS approach to the same runway with different minima, compare the missed approach procedures.

Bob Gardner
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Bob, that shouldn't negate LPV. A missed approach obstacle in Section 2 would result either in a higher DA or a missed approach climb gradient. As Russ says, it is mostly about obstacle in the final approach segment and often the lack of a $$$ vertical survey.
 
When wondering why you don't have the same minimums for both ends of the same runway, look at the approach lighting. 5N8 rw 31 has REIL, 13 has zip. When I started flying IFR, there were "night minimums in addition to "day minimums." They did away with "night" somewhere around late 60's or early 70's. Since, all procedures meet both requirements.
There's a similar situation about 20 minutes up the road from my house. Non towered field with two intersecting rw's. four rw ends with four GPS procedures. Three include LPV's the fourth (like 5N8) does not. Three have at least REIL. Guess which one doesn't. I know from experience that one is a what is called a "black hole approach". Why use it when there are three other choices? A little downwind may even be acceptable. I've never been to 5N8, I might try 13 in daylight.
 
While it may have been different in the past, today in the U.S. presence or absence and type of lighting has no effect on the type of approaches that can be established, nor does it affect the DA/MDA. What it does affect is the visibility minimums, and whether the approach can be flown at night.
 
Actually Russ, we check notams in planning to find the inop components & visual aids so we can go to the table to derive our proper minima. Applies to procedures in Echo through Bravo airspace. Also determines whether or not a LPV procedure can even be authorized for a particular RW. Example: 5N8.
 
Maxnr said:
Actually Russ, we check notams in planning to find the inop components & visual aids so we can go to the table to derive our proper minima. Applies to procedures in Echo through Bravo airspace. Also determines whether or not a LPV procedure can even be authorized for a particular RW. Example: 5N8.
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You're talking about OpSpec-type stuff and adjustments to minimums by company policy, I'm talking about the published procedures and establishment of the published minima.

5N8's lack of REILS on runway 13 does not prevent establishment of LPV minimums. There are lots of airports out there with LPV and no approach lights or REILS. Approach lights can get the procedure a lower published visibility if they're the right type and some other factors allow reduced visibility. REILS don't benefit a procedure as far as published minimums go.
 
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Wannfly asked a pretty cool question: ""Why does the two ends of the single RW at 5N8 have different minima? Why only one RW rates a LPV?" One would think that the electronic signal from space would beat down on both sides of the airport equally. Two replies cited obstacles for 13 that 31 doesn't have. Two others mentioned missed approach procedures. I mentioned lighting or lack of. I also mentioned a note indicating a Threshold crossing height. TCH is a clue that something is concerning about a RW 13 approach. Sorry, I didn't look any deeper. I got a life. One reply quickly informed us that TCH's were either 40 feet or 60. Well that was the "what" but not the"why".

I mentioned that lighting, lack of it or other components or other visual aids routinely affects minima. A quick reply directed me to my OPSPECS. I don't have any under 91. That table is in the Jepps or with the procedures.

I looked up 5N8 in the directory. Obstacles: There is a road 435 feet from the approach end of 31. As for 13, there is a 15 foot tree 540 from the approach end. However there is train traffic 30 feet from the approach end.

Back in my working pilot days, I picked up and dropped off at a facility where an elevated RR track crossed the N end our N/S RW. The train would suddenly enter from the woodline stage right. Couldn't hear it in the cockpit lined up for a north departure with both engines at full tilt boogie. Attempts to determine who has right of way, a train engaged in interstate commerce or an aircraft conducting air commerce were not fruitful. We just posted the train schedule in the flight planning room.
 
Maxnr said:
I mentioned lighting or lack of.
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Again, lighting or lack thereof has no bearing on establishment of an LPV DA. Approach Lights can decrease the minimum visibility required if they are of the right type. ref: FAAO 8260.3D, Table 3-3-1 and surrounding paragraphs and tables.

I also mentioned a note indicating a Threshold crossing height. TCH is a clue that something is concerning about a RW 13 approach. Sorry, I didn't look any deeper. I got a life. One reply quickly informed us that TCH's were either 40 feet or 60. Well that was the "what" but not the"why".
Click to expand...

Having a TCH is NOT a "clue that something is concerning". Most approaches chart a TCH * - it's simply the height above the threshold that the glidepath crosses the threshold at. They're not "either 40 or 60" feet, I said the usual range is 40 - 60 feet. Ref: FAAO 8260.3D, Table 10-1-1.

Why is there a TCH? Well, how high would you like to cross the threshold at? You can't cross it at zero. The touchdown zone markers are 1000 feet down the runway because that's approximately where an airplane on an instrument approach is expected to touch down. At a 3.00 degree glidepath, a 50 ft TCH intersects the runway 954 feet from the threshold. So the typical value is about 40 - 60 feet, dependent on several other factors, one of which is "what is the VGSI set at?"

* TCHs are not charted on circling-aligned approaches, for example, and in some other cases due to what are known as "visual segment obstacles"

I mentioned that lighting, lack of it or other components or other visual aids routinely affects minima. A quick reply directed me to my OPSPECS. I don't have any under 91. That table is in the Jepps or with the procedures.
Click to expand...

You stated that a lack of REILS is a factor in determining why 5N8 doesn't have LPV minimums to runway 13. That is not true. Lots of airports have LPV minimums but no REILS. Even if a runway has REILS, their presence alone does not have any effect on either DA or visibility minimums, at least in the U.S. Even a full approach light system has no effect on DA.

You stated that "we check notams in planning to find the inop components & visual aids so we can go to the table to derive our proper minima", in response to my comment about lighting having no effect on the DA. If you are in fact deriving your own (higher) DA based on lighting outages, then what you are doing is above and beyond what Part 91 requires (hence my OpSpec statement). Yes, if there is an approach lighting system installed, and it is out of service, then you may need to increase your visibility requirements using the Inoperative Components table, the Jepp charted values, or the Inoperative note on the chart. But that's visibility, not DA.

All of the posts above have given many good, possible reasons that 5N8 runway 13 does not have LPV. It could range anywhere from "obstacle environment" to "nobody has asked for one to be developed yet". The only way to know for certain is to contact the FAA at the website I linked above. My understanding is that they do respond fairly quickly.
 
RussR said:
Again, lighting or lack thereof has no bearing on establishment of an LPV DA. Approach Lights can decrease the minimum visibility required if they are of the right type. ref: FAAO 8260.3D, Table 3-3-1 and surrounding paragraphs and tables.
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Russ,

Do you have an example of a published LPV with a 200 HAT DA, and no ALS?

Thanks,

Wally
 
aterpster said:
Russ,

Do you have an example of a published LPV with a 200 HAT DA, and no ALS?

Thanks,

Wally
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Sure, four in my part of the world -
CSM RNAV (GPS) RWY 17R and 35L
CHK RNAV (GPS) RWY 18
SWO RNAV (GPS) RWY 35

As you know, LPVs were originally limited to 250 HAT. Then for a while you could have 200 HAT but only if there was also an ILS to that runway. Now it's 200 HAT as long as the surfaces are clear (and it's within the WAAS coverage area for 200 HAT, which is all of the CONUS). As a result, you still see a lot of 250 HAT LPVs out there just because they haven't yet had a full amendment for other reasons.
 
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RussR said:
Sure, four in my part of the world -
CSM RNAV (GPS) RWY 17R and 35L
CHK RNAV (GPS) RWY 18
SWO RNAV (GPS) RWY 35

As you know, LPVs were originally limited to 250 HAT. Then for a while you could have 200 HAT but only if there was also an ILS to that runway. Now it's 200 HAT as long as the surfaces are clear (and it's within the WAAS coverage area for 200 HAT, which is all of the CONUS). As a result, you still see a lot of 250 HAT LPVs out there just because they haven't yet had a full amendment for other reasons.
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Many thanks Russ!
 
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