dr1980
Topic Author
Posts: 113
Joined: Tue Jun 14, 2016 9:55 pm

Category 1 ILS DH Variations

Tue Apr 23, 2019 3:59 pm

Hello, given that 200 feet is the most typical CAT1 ILS decision height, I’m curious what kind of local conditions could cause this number to be higher? Flightsimming with charts I’ve seen 215, 250 etc on occasion and I wasn’t sure why.

Thanks!
Dave/CYHZ
 
LH707330
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Re: Category 1 ILS DH Variations

Tue Apr 23, 2019 5:27 pm

Some areas have difficult climbs on the missed, or require some other action that demands more time, which is why they move the DH up.
 
thepinkmachine
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Re: Category 1 ILS DH Variations

Tue Apr 23, 2019 5:46 pm

Also, there might be obstacles before the runway, rising the decision height. 200 ft is the minimum DH for CAT 1, it can always be higher.
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Starlionblue
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Re: Category 1 ILS DH Variations

Wed Apr 24, 2019 1:38 am

A couple of examples.

ILS 36 at WAMM - Manado Ratulangi. High terrain on the missed approach. Cat I minimum is 278-316 feet AGL*. https://saripedia.files.wordpress.com/2010/08/manado.pdf
ILS 04 at WAPP - Ambon Pattimura. High terrain on the missed approach. Cat I minimum is 469-489 feet AGL*. That missed approach path looks like it would induce some picker factor if flown at night btw. :)https://saripedia.files.wordpress.com/2010/08/ambon.pdf
ILS 16 at YMML - Melbourne Tullamarine. High terrain on final. Cat 1 minimum is 208 feet AGL. https://www.crc.id.au/xplane/charts/DAPS-2019-FEB-28/Melbourne%20(YMML).pdf

* depending on category.
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JustAnFO
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Re: Category 1 ILS DH Variations

Wed Apr 24, 2019 11:57 am

A common reason for increased DH in the US is reduced/non-standard approach lighting.


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LH707330
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Re: Category 1 ILS DH Variations

Wed Apr 24, 2019 4:56 pm

JustAnFO wrote:
A common reason for increased DH in the US is reduced/non-standard approach lighting.


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A good example of that is KTIW, the plate for the ILS 17 says it's 494/200, but there was a NOTAM for a while that put it up to 655 while they were fixing it.
 
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Web500sjc
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Re: Category 1 ILS DH Variations

Wed Apr 24, 2019 9:48 pm

The ILS 34 at KROA has minimums that are 700AFE due to the climb requirements for the missed. I do not have to question why the minimums are so high, but I do have to question why they even bothered to have an ILS.
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N1120A
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Re: Category 1 ILS DH Variations

Thu Apr 25, 2019 3:32 am

Other factors are noise abatement and proximity to other airports. For example, KHHR's LPV approach (CAT I quality) has minimums more than twice 200', and that is partly because KHHR's runway is recessed into the ground a bit and also because of the need of separation from LAX, TOA and LGB. KMYF's ILS and LPV approaches both had HATs of 200', but were first NOTAM'd to 250' and are now published as such. The reason there is likely noise abatement.
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dr1980
Topic Author
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Re: Category 1 ILS DH Variations

Fri Apr 26, 2019 9:07 pm

Thanks for the info!
Dave/CYHZ
 
Thenoflyzone
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Joined: Sun Jan 07, 2001 4:42 am

Re: Category 1 ILS DH Variations

Sat Apr 27, 2019 12:50 am

JustAnFO wrote:
A common reason for increased DH in the US is reduced/non-standard approach lighting.


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:checkmark:

Same in Canada.
us Air Traffic Controllers have a good record, we haven't left one up there yet !!

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