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I was wondering wether each segments of the approach has different minimum obstruction clearance? (E.g. initial, intermediate and final) From both terrain and man made obstacles.

If possible i would like it to be from ICAO, hence PANS-OPS. But any TERPS answers i would happily accept.

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Each segment of the approach has different MOC (Minimum Obstacle Clearance). Below I have quoted the MOC from ICAO DOC 8168 Volume II for each of the different segments of the approach.

Initial segment (Part I - Section 4, Chapter 3.3.4):

The obstacle clearance in the initial approach primary area shall be a minimum of 300 m (984 ft). In the secondary area, 300 m (984 ft) of obstacle clearance shall be provided at the inner edge, reducing linearly to zero at the outer edge.

Intermediate segment (Part I - Section 4, Chapter 4.3.2.1):

A minimum of 150 m (492 ft) of obstacle clearance shall be provided in the primary area of the intermediate approach segment. In the secondary area, 150 m (492 ft) of obstacle clearance shall be provided at the inner edge, reducing to zero at the outer edge.

Final segment, for non-precision straight-in approaches without vertical guidance (Part I - Section 4, Chapter 5.4.3.1):

The OCA/H for a straight-in, non-precision approach where the angle between the track and the extended runway centre line does not exceed 5 degrees shall provide the following minimum obstacle clearance (MOC) over the obstacles in the final approach area: a) 75 m (246 ft) with FAF; and b) 90 m (295 ft) without FAF.

Note that precision approaches and approaches with vertical guidance (ILS, LPV, LNAV/VNAV etc.) do not have a fixed MOC, and the obstacle clearance is calculated using more advanced methods.

Initial missed approach segment (Part I, Section 4, Chapter 6.2.1.3):

Obstacle clearance in the initial phase. In the initial missed approach area, the minimum obstacle clearance shall be the same as for the last part of the final approach area except where the extension of the intermediate missed approach surface backwards towards the missed approach point requires less clearance. (See Figures I-4-6-4 and I-4-6-5.)

Intermediate missed approach segment (Part I, Section 4, Chapter 6.2.2.3.1):

In the intermediate missed approach phase, the minimum obstacle clearance shall be 30 m (98 ft) in the primary area, and in the secondary area the minimum obstacle clearance shall be 30 m (98 ft) at the inner edge, reducing linearly to zero at the outer edge.

Final missed approach segment:

In the final missed approach phase of a straight missed approach the minimum obstacle clearance shall be 50 m (164 ft) (Cat H, 40 m (132 ft)) in the primary area, reducing linearly to zero at the outer edge of the secondary area.

Figure I-4-6-4 and I-4-6-5: enter image description here

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The FAA lays this out in Order 8260.3c the three main relevant sections for requirements, level flight and climbing/decent segments are:

2-1-2. Required Obstacle Clearance (ROC). This order specifies the minimum measure of obstacle clearance considered by the FAA to supply a satisfactory level of vertical protection. The validity of the protection is dependent, in part, on assumed aircraft performance. In the case of TERPS, it is assumed that aircraft will perform within certification requirements.

...

2-1-3. Level OCS. The level OCS concept is applicable to “level flight” segments. These segments are level flight operations intended for en route, STAR, feeder, initial, intermediate, and NPA final approach segments. A single ROC value is applied over the length of the segment. These values were determined through testing and observation of aircraft and pilot performance in various flight conditions. Typical ROC values are: 1000 feet (2000 over designated mountainous terrain) for en route, STAR, and feeder segments, 1000 feet for initial segments, 500 feet for intermediate segments, and 250-500 feet for final segments.

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2-1-4. Sloping OCS. The method of applying ROC, in segments dedicated to descending on a glidepath or climbing in a departure or missed approach segment, requires a different obstacle clearance concept than the level OCS because the ROC value must vary throughout the segment. The value of ROC near the runway is relatively small and increases throughout the segment.

The document is lengthy and lays out various formulas and charts, to keep form copying the whole thing here please reference the document directly for anything more specific.

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