What is OCA(H) exactly

[felixthecat]

What exactly is the OCA(H) If you flew at the OCA(H) would you hit the highest obstacle or is there a predefined difference between the height of the obstacle and the OCA(H)?

[bookworm]

There is a minimum difference -- Minimum Obstacle Clearance (MOC).

For a non-precision approach:

90 m (295 ft) without FAF
75 m (246 ft) with FAF
(FAF = final approcah fix)

For a precision approach it's more complex.

[felixthecat]

The minimums for a precission approach a Cat I for example would be the higher of the OCA(H) or 200ft, whichever is the higher (some companies add 50ft to the OCA(H) )
What Im after is for example say at a sea level airfield there is an aerial of 320ft would the OCA(H) be 320ft or would it be 320ft plus a set amount?

[bookworm]

What Im after is for example say at a sea level airfield there is an aerial of 320ft would the OCA(H) be 320ft or would it be 320ft plus a set amount?

That's what I was trying to tell you. The 'set amount' is 295 ft for an NPA with no FAF, 246 ft for an NPA with FAF, and for a precision approach it's more complex.

The 'set amount' is the Minimum Obstacle Clearance (MOC).

[felixthecat]

So your saying that the OCA (H) can never be less than 295ft (FAF)/ 246ft (No FAF)? I guess thats why the VOR/NDB minima are a minimum of 300ft

[hvogt]

The term OCA/H is defined by ICAO (for example in PANS-OPS):

The lowest altitude or the lowest height above the elevation of the relevant runway threshold or the aerodrome elevation as applicable, used in establishing compliance with appropriate obstacle clearance criteria.

So OCA/H depends on the individual circumstances of each procedure, as bookworm already mentioned.

[The Snake]

OCA/H is published by the applicable state. And is official.

MDA/H, or DA/H, is calculated by your company/Jepessen etc etc, based on the published OCA/H. This can be flexible, as long as it's NOT below the OCA/H.

Purely for your information.

Bye

[Tasmaniac]

Chaps. Reopening this discussion after a few years!

Humberside (EGNJ) ILS for a Cat B aircraft is stated as OCA 230ft on the UK AIP plates. Jeppesen et al have the DH as something higher, typically 274ft. I totally get that the height difference (in this case 44ft) is entirely at the desire of the commercial company making the plates. I also get that a company's Operations Manual may require a extra (additional) height to be added to the DH..... so it is quite possible that for an individual company, the DH needs to be raised by (say) an additional 50ft to 324ft.

My question is this.....if there is no stated requirement in the OM to use a specific company's instrument plates (and consequently the pilot elects to use the UK AIP plates), and no stated requirement to add any additional height to approach minima, is the pilot legal (and safe!) descend on the ILS to OCA (230ft) as stated on the UK AIP plates???

[FlyingStone]

NCO.OP.111/CAT.OP.MPA.110.

DA/MDA is a higher of the OCA or system minima. Cat 1 ILS minima cannot be lower than 200ft above the landing threshold, so descending to 230 feet without appropriate visual references is not legal.