# Instrument Approach Procedures: Segments, Minima, and Missed Approach Criteria

> Review instrument approach segment logic from IAF to missed approach, including obstacle clearance minima OCA/H and operational minima MDA/H.

- **Subject:** 010 — Air Law
- **Section:** 010-06 — Aircraft Operations
- **Topic code:** 010-06-04
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/air-law/aircraft-operations/approach-procedures-icao-doc-8168-volume-i/

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Instrument approach procedures are divided into segments with specific purposes and obstacle clearance criteria.

## Segments of the Approach

1.  **Arrival Segment**: Transition from en-route to approach (up to the IAF).
2.  **Initial Approach Segment**:
    *   From the **IAF** (Initial Approach Fix) to the **IF** (Intermediate Fix).
    *   The aircraft maneuvers to enter the intermediate segment.
3.  **Intermediate Approach Segment**:
    *   From the **IF** to the **FAF** (Final Approach Fix) or FAP.
    *   Purpose: Configure the aircraft (speed, flaps) and prepare it for final. The descent gradient is as shallow as possible.
    *   Obstacle clearance in primary area reduces from 300 m to **150 m (492 ft)**.
4.  **Final Approach Segment**:
    *   From the **FAF/FAP** to touchdown or the MAPt.
    *   Purpose: **Alignment and descent** for landing.
    *   **Gradients**: Optimum **3.0° (5.2%)**. Maximum for Cat A/B is **6.5% (3.7°)**.
5.  **Missed Approach Segment**:
    *   From the **MAPt** (Missed Approach Point).
    *   Purpose: Protect the aircraft from obstacles during the climb if a landing is not executed.

## Minimum Altitudes (OCA/H vs MDA/H)

*   **OCA/H (Obstacle Clearance Altitude/Height)**: Calculated in design. It is the lowest altitude/height at which the missed approach must be initiated to guarantee obstacle separation.
*   **MDA/H (Minimum Descent Altitude/Height)**: Specified for the operation (never lower than OCA/H). Descent below MDA/H shall not be made unless:
    1.  Visual reference is established.
    2.  The threshold is in sight.
    3.  Obstacle clearance for landing is ensured.

## Precision vs Non-Precision Approach

*   **Precision**: Uses lateral and vertical guidance (ILS, MLS). The final segment starts at the **FAP** (Final Approach Point), where the intermediate altitude intercepts the glide path.
    *   If the Glide Path fails, it becomes a **non-precision approach**.
*   **Non-Precision**: Lateral guidance only (VOR, NDB, LOC). Uses **FAF** and step-down minimum altitudes.

## Circling Approach (Visual Maneuvering)

*   It is a visual maneuver following an instrument approach.
*   **Loss of Visual Reference**: If visual contact is lost during circling:
    1.  Initiate a **climbing turn towards the landing runway** (within the protected area).
    2.  Intercept and execute the **missed approach** procedure of the original instrument approach (the one flown before circling).

## Fixes and Errors
*   **MAPt (Missed Approach Point)**: Can be a fix, a DME distance, or the intersection of the Glide Path with the DA/H. If the missed approach is initiated *before* the MAPt, the pilot must fly to the MAPt before turning to stay within protected airspace.

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