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

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.

Maneuver Definitions

• 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).

Tolerance Factors

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.

Aircraft Categories

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