Use of Performance-Based Navigation (PBN) in Operations

062-07-03Pablo Asensio Martínez2026-04-012 min

The use of PBN introduces specific concepts and functionalities in navigation systems to improve airspace efficiency and capacity.

Waypoint Types

  • Fly-by Waypoint: The pilot or system anticipates the turn to avoid overshooting the next flight segment. The turn begins before reaching the waypoint. It is the standard form of turning in RNAV routes.
  • Fly-over Waypoint: The aircraft must physically fly over the waypoint before initiating any turn. Used when it is necessary to follow a specific path due to obstacles or procedures (e.g., MAPt).

Fixed Radius Paths (FRP)

These are precise curved paths that the RNP system must be capable of flying.

1. Radius to Fix (RF) Leg

  • Use: Terminal and Approach procedures.
  • Definition: Defined by a radius, an arc length, and a fix (endpoint).
  • Requirement: Requires autopilot or flight director with "roll-steering" capability.
  • Accuracy: Maintains the same accuracy (RNP) during the turn as in straight segments.

2. Fixed Radius Transition (FRT)

  • Use: En-route procedures.
  • Purpose: Allows closer parallel routes in upper airspace.
  • Standard Radii:
    • 22.5 NM for high altitude routes (above FL 195).
    • 15 NM for low altitude routes.

Specific System Functions

  • Lateral Offset (SLOP - Strategic Lateral Offset Procedure):
    • Capability to fly parallel to the defined route at a specific distance (usually in 1 NM increments up to 20 NM).
    • Used for contingencies or to reduce collision risk due to loss of vertical precision (wake turbulence).
    • The system usually cancels the offset automatically in terminal areas, approaches, holds, or turns >90°.
  • ARINC 424 Path Terminators: Navigation database coding standard that defines how the FMS interprets and flies procedures (SIDs, STARs, IAPs). Defines 24 segment types (e.g., RF, TF - Track to Fix, CF - Course to Fix).

Key Differences

  • Fly-by vs RF: A fly-by turn varies its radius and start point according to speed and wind (it is not a fixed ground track). An RF turn is a fixed ground track (constant radius), regardless of speed or wind.