PANS-OPS Definitions and Abbreviations: Protection Areas, Segments, and Tolerances

010-06-02Pablo Asensio Martínez2026-03-272 min

This section introduces key concepts from ICAO Document 8168 (PANS-OPS), fundamental for the design of instrument flight procedures.

Areas and Margins

Protection Areas: When designing a procedure, the vertical airspace of a segment is divided into:
- Primary Area: Central zone located symmetrically on both sides of the track.
  - On straight segments, its width is half of the total width.
  - In turns without track guidance, the total width is considered primary area.
  - Full Minimum Obstacle Clearance (MOC) is provided across its entire width.
- Secondary Area: Outer lateral zones.
  - Obstacle clearance reduces linearly from the primary area margin to zero at the outer edge.
  - On straight segments, each secondary area has a width of one quarter of the total.

Circling Approach (Visual Maneuvering): It is the phase after completing an instrument approach that positions the aircraft for landing on a runway not suitable for a straight-in approach (due to excessive alignment or descent gradient).
Final Approach Segment (FAS): Segment where alignment and descent for landing are performed.
DER (Departure End of Runway): The end of the runway available for the ground run of an aircraft taking off (opposite to the landing threshold).

Several factors affect the accuracy of a fix and its associated tolerance area:

Airborne receiver tolerance: Error in aircraft equipment (e.g., VOR, ADF).
Ground station tolerance: Margin of error of the transmitting station.
Flight technical tolerance: Accuracy with which the aircraft is piloted, display errors, etc.
Note: Meteorological tolerance is not considered a direct factor in the geometric accuracy of the fix.

The most significant factor affecting the airspace required and visibility for instrument maneuvers is the aircraft speed.