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

010-06-04Pablo Asensio Martínez2026-03-272 min

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.