FMC Databases: AIRAC Navigation Data and Performance Models

022-11-02Pablo Asensio Martínez2026-03-272 min

Overview

The Flight Management Computer (FMC) relies on two primary databases to perform its functions: the Navigation Database and the Performance Database. Additionally, a temporary storage area allows pilots to define custom waypoints.

Navigation Database (NDB)

The Navigation Database is a digital repository containing aeronautical information essential for lateral navigation and flight planning.

Content

  • Airports & Runways: Locations, elevations, lengths.
  • Navaids: VORs, NDBs, DMEs, and their frequencies.
  • Intersections/Waypoints: Coordinates and identifiers.
  • Airways: Enroute structure.
  • Procedures: SIDs (Departures), STARs (Arrivals), and Approaches (ILS, RNAV, etc.).
  • Company Routes: Pre-defined routes used by the airline.
  • Magnetic Variation: Data to convert True North to Magnetic North.

Updates & Validity (AIRAC)

  • The database follows the AIRAC cycle (Aeronautical Information Regulation and Control) and is updated every 28 days.
  • The FMC typically holds two cycles:
    • Active: The current valid database.
    • Standby/Second: The adjacent cycle (previous or next).
  • Read-Only: The core data is read-only to ensure integrity. Pilots cannot modify or delete standard waypoints or procedures.
  • Pilot Action: Pilots verify the validity dates during pre-flight checks on the IDENT page. Changing the active database typically deletes the active flight plan.
  • Note: Terrain and obstacle data are usually stored in the EGPWS database, not the FMS Navigation Database.

Performance Database

The Performance Database contains static data specific to the aircraft's airframe and engine model.

Content

  • Engine Model: Thrust characteristics, fuel flow parameters at various power settings and altitudes.
  • Aerodynamic Model: Drag polars (clean and configured), lift characteristics.
  • Speed Limits: VMO/MMO, flap signaling speeds.
  • Optimization Data: Optimum altitudes, maximum altitudes, and recommended cruise speeds (ECON).

Purpose

The FMC uses this data to calculate:

  • Thrust Targets: N1 or EPR settings for Takeoff, Climb, Cruise, and Go-Around.
  • Predictions: Fuel consumption, Estimated Time of Arrival (ETA), and Top of Descent (TOD) points.
  • Speeds: V1, VR, V2, and Green Dot (best lift-to-drag) speeds.

Maintenance Factors

While pilots cannot alter the core model, maintenance personnel can enter Drag Factors or Fuel Flow Factors to account for airframe aging and engine degradation, ensuring predictions remain accurate.

User-Defined Waypoints

Since pilots cannot modify the main database, the FMS provides a Supplemental or Temporary database for pilot-created waypoints. These are erased when the main navigation database is updated.

Creation Methods

  1. Lat/Long (LL): Direct coordinate entry (e.g., N45W030).
  2. Place/Bearing/Distance (PBD): Defines a point based on a known fix (e.g., LMG/330/20 - 20NM on the 330 radial from LMG).
  3. Place-Bearing/Place-Bearing (PBX): Defines a point at the intersection of two radials (e.g., LMG330/CGC090).
  4. Along Track (PD): A distance before or after a waypoint along the current flight path.