Change in OCA(H)

[felixthecat]

If a chart Notam gives a change in OCA(H) say due to a crane or the like when does it effect the DA(H) ?

[flyburg]

Published minima shall be raised as follows:

— CAT III approach Not applicable.

— CAT II approach Changes in CAT II OCH to a value of 100 ft DH or below may be disregarded. If a CAT II OCH has been raised to a value in excess of 100 ft DH, a CAT II approach is not allowed, unless an adjusted DH is published in OM Part C3.

— CAT I approach/RNP APCH APV (Approach procedure with vertical guidance/Baro VNAV) or RNP AR APCH. Compare DA with NOTAM OCA and use the highest value as DA. If applicable, increase the RVR in accordance with the standard CAT I landing minima as published in OM Part C2.

— Non-precision approach/RNP APCH NPA (Non precision approach/LNAV only) Compare MDA with NOTAM OCA and use the highest value as MDA. If applicable, increase the RVR in accordance with the standard non-precision approach landing minima as published in OM Part C2.

[felixthecat]

Thank you for the info, what was the reference? Thanks :)

[aterpster]

The FAA makes it a lot simplier. The NOTAM includes the temporary DA/MDA and visibility/RVR values.

[C212-100]

flyburg,

Can you help by telling me in which document can I find that info?

Thanks!

[9.G]

C212-100, most states only publish OCA/OCH Jepp simply renames it into DA/DH or MDA/MDH. Basic principle if OCA is higher than published mins use the higher value. :ok:

[flyburg]

Copy paste straight from my company's Operations manual (part A).

[BOAC]

Surely all those seeking 'references' simply need to think about the logic? You surely do not need them?

CatIII - doesn't matter - if the 'new' obstacle is that close to the runway, no CatIII

Ditto CatII (<100ft)

CatI/NPA - self-explanatory - see 9.G

OCA/H is a physical thing:: DA/H is a crew/company/regulatory thing based on OCA/H and never less than.

[felixthecat]

I wish logic always prevailed but in aviation it often doesn't…I was wondering if for example there was a specific increase in minima per increase in OCA for example….

[9.G]

CatIII - doesn't matter - if the 'new' obstacle is that close to the runway, no CatIII Boac, OCA/H is based on obstacle assessments of approach and missed approach thus as long as there's a published DH, even for CAT III, a raised OCH is to be used. My take on that. :ok:

[flyburg]

A cat III approach has no OCH, only obstacle free zones! Hence if an OCH is published no CAT III allowed, same for a CAT II approach with an amended by notam OCH above 100.

Have some background info on this but unfortunately unable to copy/paste.

BOAC is right though :eek: DA(H) are system, state or crew minima and as such published, however if a OCA(H) exists which is higher than those minima then the higher value must be used ( limitations regarding CAT II/III observed as in my first post).

Operations below DA/MDA are see and avoid, hence an OCA! For operation below DA on cat II/III see and avoid is not acceptable.

Hope this makes sense, I find it easier to understand than to explain!

[flyburg]

9.g

Sorry, your statement, not completely correct!

Regulatory agencies will establish DA(h)/MDA(H). For example, minimum DA for a cat I is 200, minimum MDA for a VOR/LOC is 250, minimum MDA for an NDB is 300 etc, etc. this under EU OPS for example.

States publish OCA and it is then to the operator to derive a DA/MDA taking into account the above regulatory minimums or crew minimums or aircraft minimums.

What Jeppesen does is to take the regulatory minimums and compute a DA which cannot be less than the the state published OCA. They don't take into account crew or aircraft minima. That is upto the operator. I believe for example that US FAA requires minimal experience to operate to the lowest minima! And some aircraft might need higher minima due to systems.

So, they don't rename it! They use it to DERIVE minimums!!

An example, a state publishes a OCA for a runway as 215'. If there is a ILS approach the DA would be 215'( limited by OCA). If there is an LOC/VOR APP the MDA would be 250'( limited by regulatory).

In case of CAT II/III it gets a little more complicated because they use OBSTACLE FREE ZONES or OFZ, this because the see and avoid principle does not apply, in case of CAT II as long as OCA does not exceed 100' still okay, in case of CAT III no OCA exists.
Hope this makes sense!

[9.G]

So, they don't rename it! They use it to DERIVE minimums!! Absolutely, poorly chosen wording on my side. Agreed on CAT II though OFZ is supposed to be 150 ft in height above the airdrome as well but then again there's three different zones. CAT III exists with DH of 50 ft thus my assumption. Not sure what you mean with see and avoid though.

P.S. certainly appreciate more reading material on this topic. :ok:

Out of interest take randomly any of the European AIP published charts and compare OCA/H with the published mins of Jepp. See how many differences will find. I found 0.

[Mikehotel152]

Logic often works well. If the revised OCA(H) is below the DA, you will be safe.

I worked on compiling minima for a major chart manufacturer. We would take the OCA(H) from the State's AIP, stick it in a computer programme and calculate the CATI & II and minima. IIRC the actual DA was usually about 10% above the OCA(H) and always above the regulatory minima.

CATIII approaches obviously require a different system because they're based on the nature of the undulating terrain on the approach. I can't remember the details, especially at this time of the night.

[flyburg]

I may be wrong, but it is my understanding that for operations below the decent limit the see and avoid principle applies. For example on non precision approaches. At some point you have to decent below the OCA to land.
The designers will design a instrument approach to guide you down free of obstacles, but at some point you will take over visually. Think of some approaches where you have really high mins due to high obstacles around like mountains. The designers can only get you so low. At some point you will have to decent below the altitude they can get you. Hence, see and avoid.

Pure theoretical discussion though as there will generally be few obstacles between you and the runway but you will decent below obstacles on which the OCA is based.

[9.G]

flyburg, I see whatcha saying. There's also OCS which has to be complied with or noted otherwise if that's not the case. The purpose of IAP is to position you to able to complete the landing by visual means primarily. It's not like you're required to perform evasive maneuvers for obstacle avoidance after you broke visual. You're entirely correct on the CAT III matter. I did a little digging and found following:
OBSTACLE SURFACES
Obstacle clearance criteria for Category 2 operations are in ICAO PANS-OPS Doc 8168. An Obstacle Free Zone (OFZ) is the airspace below 150 feet above the established airport elevation and along the runway and extended runway centreline, that is required to be kept clear of all objects; except for frangible visual NAVAIDs that need to be located in the OFZ because of their function, in order to provide clearance for aircraft landing or taking off from the runway, and for missed approaches. If the Obstacle Free Zone (OFZ) requirements cannot be fully met, the National Regulatory Authority should be consulted as to the feasibility of specific aeroplane types carrying out Category 2 operations within the obstacle limitations pertaining. This applies particularly if a Category 2 DH exceeds 150ft, which is the top of an OFZ.

The obstacle clearance criteria for Cat 3 operations are satisfied by the provision of an OFZ. Thanx for the info. :ok:

[Sir George Cayley]

With the introduction of Lower than CAT l and Other than CAT ll how would an operator with suitably equipped a/c deal with the scenario?

SGC

[9.G]

SGC, this is DH for Lower than Standard Category I Operations

1. Decision height.

A lower than Standard Category I Operation decision height must not be lower than:
(i) the minimum decision height specified in the AFM, if stated; or
(ii) the minimum height to which the precision approach aid can be used without the required visual reference; or
(iii) the OCH for the category of aeroplane; or
(iv) the decision height to which the flight crew is authorised to operate; or
(v) 200 ft.
whichever is higher.

No change in the DH but in required RVR

Precision approach — Category II and other than Standard Category II operations 1. General.
(i) A Category II operation is a precision instrument approach and landing using ILS or MLS with:
(A) A decision height below 200 ft but not lower than 100 ft; and
(B) A runway visual range of not less than 300 m.
(ii) An other than Standard Category II operation is a precision instrument approach and landing using ILS or MLS which meets facility requirements as established in paragraph (iii) below with:
(A) A decision height below 200 ft but not lower than 100 ft; and
(B) A runway visual range of not less than 350/400 m.
(iii) The ILS/MLS that supports other than a Standard Category II operation shall be an unrestricted facility with a straight in course (≤ 3o offset) and the ILS shall be certificated to:
(A) Class I/T/1 for operations down to 450m RVR and to a DH of 200 ft or more; or,
(B) Class II/D/2 for operations in RVRs of less than 450m or to a DH of less than 200 ft.
Single ILS facilities are only acceptable if Level 2 performance is provided.

2. Decision Height.

An operator must ensure that the decision height for:
(i) Other than Standard Category II and Category II operations is not lower than:
(A) The minimum decision height specified in the AFM, if stated; or
(B) The minimum height to which the precision approach aid can be used without the required visual reference; or
(C) The OCH for the category of aeroplane; or
(D) The decision height to which the flight crew is authorised to operate; or
(E) 100 ft.
whichever is higher.

NO change in the DH value here as well but different requirements for the autoland systems and RVR. :ok: