Changed OCA/H in NOTAM, what happens to DA/H MDA/H?

[donpedro]

As stated in title.

I have seen NOTAM stating new higher OCA(H) XXX feet, but nothing about DA/H.

Usually people would set that new higher as the DA/MDA.

But what happens with the margins?

As it says in EU-OPS and Annex 6, DA/MDA is constructed from OCA/H by adding and operational margin depending on several factors.

Anyone who could recommend me what altitude I can follow the GS down to when there is a new OCA/H in NOTAM higher than old DA/H on plate?

Cheers

[Gary Lager]

Short answer - follow the GS down to the new OCA or DA, whichever higher.

The DA cannot be lower than the OCA or the system (ILS/VOR/etc) minima. If the OCA goes up by 50ft, so must the DA. The margins are still there, albeit 'underneath' the extra 50ft you just added on for the new crane/tree/whatever.

You do also need to adjust your visibility minima under EU-OPS, you need to refer to the tables for calculating aerodrome minima in your Ops Manual/Aerad/Jepp Text manual.

[donpedro]

Cheers Gary Lager.

Although without knowing the previous margin from OCA to DA I am still a bit confused.

Say the old DA was 240 feet = OCA + margin, and the new oca is temporarily upped to 360 feet.

Now as I didn't have a clue of what the difference in the old DA was between DA and OCA, it is not possible to add the required margin to the new OCA.

And technically it is not allowed to fly the GS down to the OCA of 360feet since this includes no margin.

Am I thinking in circles here ? :)

[no sig]

NOTAM's won't, normally, specific a DA/H as these minima (in commercial operations) are defined by the operator.

[donpedro]

no sig: Yes I'm with you on that, the NOTAM states a change to OCA/H while the current Jeppe plate we use states a DA/H that is lower than the new OCA/H per notam.

1. NOTAM tells OCA/H for cat C is 403/262 for ILS Z and Y in Alicante RWY10
2. Jeppe plate says DA/H for cat C is 376/234 for ILS Z and Y for same RWY

3 Spanish AIP AD2 states OCA/H for that approach was 376/234. The same as Jeppe DA/H that I thought was going to include a margin

So since there was no difference between OCA/H and DA/H in Alicante before I assume the new OCA/H will also be the new DA/H for us using Jeppesen.

[donpedro]

Cut out from Spanish AIP AD2 Alicante, Jeppesen plate and NOTAM.

The OCA/H on spanish AD2 is same as DA/H on Jeppesen.

So then I assume OCA/H per NOTAM will be the new DA/H

http://www.ladda-upp.com/bilder-a/obstacle_clearance_height-429.jpg (http://www.ladda-upp.com/bilder/23317/obstacle-clearance-height)

[Gary Lager]

Correct.

In your earlier post you stated "DA=OCA + margin"...I don't think this is correct.

It ought to read "OCA = obstacle + margin"

The 'margin' you are referring (whatever it may be) to is included in the OCA. So if you get a new OCA then it includes the margin, as before.

The DA is determined by the approach type and operator minima, but cannot be less than the OCA. Another reason the NOTAM doesn't tell you a DA, is that you may be doing a VOR approach, or an SRA, or an NDB, and it's easier just to tell you the OCA/H and let you apply your own calculations.

[Sir George Cayley]

Except..

Precision = Decision so expect a DA/H, and

Non-precision = expect a MDA/H

What type of approach are we planning here? If it's an ILS or LOC/DME there's a difference.

The references you need are ICAO PANS-Ops Doc 8168 and the State AIP.
Jepps are good but not infallible. Always xref when in doubt.

Any help?

Sir George Cayley

[411A]

Another reason the NOTAM doesn't tell you a DA, is that you may be doing a VOR approach, or an SRA, or an NDB, and it's easier just to tell you the OCA/H and let you apply your own calculations.

Except in the USA, Japan, SaudiArabia...and a few other places.
OCA changes, notams denote the new DA's, MDA's etc for the various approaches.
Often times the OCA change is temporary...construction cranes, for example.

[donpedro]

cheers guys,

as you see in the link I included,

before the NOTAM even came out, cross referencing Jeppesen plate for ILS approach RWY 10 in Alicante with the Spanish AIP you find that OCA/H = DA/H.
Therefore the logic would be NEW OCA/H = NEW DA/H for this precision approach.

I think I might just have been tricked by the illustration in doc 8168 (1-4-1-9) and ICAO annex 6. Where it looks like there is a difference between OCA/H and DA/H but obviously this might only apply for special reasons.

I have been cross referencing OCA/H against DA/H for a couple of ILS approaches in various countries and it seems there is no "need" for a margin.

Thank you once again for all your replies, its great to get some input and I feel I get the hang of it now.

Cheers

[ItsAjob]

Speak to Jeppesen.

They will tell you that if the OCA in the notam is not associated with any approach procedure eg ILS, NDB etc.. you can ignore it.

If it is written ref with an approach procedure like your Alicante ILS then you must use the OCA as your minima. (As long as it is not below ICAO mins)

The problem is the local CAA dont use MDA, and they call all the minimums OCA's

[Port Strobe]

The simpler way this was explained to me was choose the greater of OCH or system minima. I'd imagine the system minima will be listed in the ops manual (ie 200' ARTE for Cat I ILS etc). The upshot being a notam may well be published for a raised OCH somewhere but if it's less than system minima it could have no impact on the minima used for the approach.