OCH vs MOC

[baobab72]

Hi everyone,
one of those doubts that creeps in your mind as you review the procedures
what is the difference between OCH and MOC?
MOC ensures obstacle clearance during an instrument approach procedure within the primary area and the inner edges of the secondary areas, while it reduces to zero at the outer edges of the secondaries, while the OCH provides obstacle clearance.
Does nt it sound like a paradox? what is the difference between them then? and shoulnd the MOC higher that the OCH?
Sorry for the dumbness of the question.

Baobab72

[Oktas8]

Doc 8168 would supply an answer for you. However, I lack a copy in front of me.

From memory, MOC is as you say and applies during the initial, intermediate, final and missed approach stages. However OCH applies in the vicinity of the landing runway, and is used to generate an MDH or DH specific to a runway. OCH might be as little as only a few tens of feet for a runway with no buildings or fences, but MDH/DH must include other factors such as absolute minimum values for the quality of the navaid serving the landing facility.