Gps as DME for non published waypoint during ILS

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TimS
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Re: Gps as DME for non published waypoint during ILS

Post by TimS »

Ok, the nerds on BT provided a rather dry answer. :D
There were differences in how the MAP was calculated. So, the difference was in where the missed started or was declared. No info on why it changed, or how it did. And I could only read so much of the TERPS manual before my eyes rolled up.
Going forward, that is no longer true for ILS CAT I and LPV. The final approach segment and MAP will be identical. As charts are revised, this will be updated and they will match.
With so many LPV approaches now, not sure how long this will take.

Tim
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Re: Gps as DME for non published waypoint during ILS

Post by TimS »

One more detail. Contact the airport manager and jointly or have them submit a request here:
https://www.faa.gov/air_traffic/flight_ ... rocedures/

They can then update the procedure charts for the LPV to match the ILS CAT I.
Not sure how it works, but I was left previously with the impression that airports with requests are processed faster than waiting on the normal rotation for a chart update.

Tim
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Re: Gps as DME for non published waypoint during ILS

Post by carym »

Just looking at this discussion I wonder if there is another difference between the LPV and ILS. Since my plane was not WAAS enabled I never looked closely into this issue. On an ILS that has a MAP at 200 feet, you can go down to 100 feet if you see any of the required lights before you can see the runway. This happened to me once going into my airport during a snow fall. I was able to see the strobes flashing short of the runway threshold, but just couldn't see the runway when I was at 200 feet. Continuing the approach down another 50 feet got me to see the runway so I could land. On a LPV approach can you go down an additional 100 feet if certain lights are visible, or are you required to go missed if you don't see the runway when at the MAP?
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Re: Gps as DME for non published waypoint during ILS

Post by Wall-e »

Cary,

That procedure applies to the LPV approach as well. Lights at 200 & runway environment by 100.
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Re: Gps as DME for non published waypoint during ILS

Post by TimS »

Wall-e wrote:Cary,

That procedure applies to the LPV approach as well. Lights at 200 & runway environment by 100.
I was taught you can descend another 100ft with lights in sight. This is often a drop from 200ft to 100ft on updated charts per the latest standard; but you need to verify with the chart. Or did I get it wrong? The reason I ask is I believe there are some mountain airports that the ILS and LPV approach MAP is much higher than 200ft.

Tim
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Re: Gps as DME for non published waypoint during ILS

Post by Chris B »

TimS wrote:I was taught you can descend another 100ft with lights in sight. This is often a drop from 200ft to 100ft on updated charts per the latest standard; but you need to verify with the chart. Or did I get it wrong? The reason I ask is I believe there are some mountain airports that the ILS and LPV approach MAP is much higher than 200ft.
Per the relevant FAR:
19.175(c)(3)(i) wrote:Operation below DA/DH or MDA. Except as provided in paragraph (l) of this section or §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

(+ more exceptions...)
The entire section applies to any approach with DA/DH or MDA.

As noted on page 2 in this thread:
At an airport with ILS lighting, ILS Cat I & LPV are functionally equivalent. Discrepancies are due to variations in MAP on older approaches (e.g., SBA), and the TERPS rules used to be different for ILS Cat I & LPV MAP. But AFAIK this is no longer the case.

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Re: Gps as DME for non published waypoint during ILS

Post by TimS »

Chris,

Nice refresher. I had the 100ft backwards. Not descent below DA/DH or MDA; but 100ft AGL.
I cannot wait for the weather to clear and get my IPC done.

Tim
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Re: Gps as DME for non published waypoint during ILS

Post by jb642DA »

Great post Chris!

A "saying" to remember this is "Lights and Color"

To descend below DA you need "lights" (approach lighting system) and to go below the last 100' (above TZE), you need "color" (ie. - red lights - the runway threshold area) as a MINIMUM.


Also I think (1) has some very good "guidance" in it - have your approach STABILIZED and under control - those last couple of hundred feet in a low vis/break out at minimums approach can still "get you"!

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;
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