비행 관리 시스템 (FMS)

Overview

The Flight Management System (FMS) is the central navigation and flight-planning computer aboard modern commercial aircraft. It integrates data from multiple onboard sensors — GPS, inertial reference systems, VOR, DME, and air data computers — to calculate the aircraft's current position, determine the most fuel-efficient route to the destination, and communicate lateral and vertical guidance commands to the autopilot and autothrottle. The FMS effectively serves as the digital brain of the aircraft's flight deck, freeing pilots from manual navigation tasks and enabling precise four-dimensional trajectory management (latitude, longitude, altitude, and time).

Early FMS units appeared on widebody jets in the late 1970s. The Boeing 767, entering service in 1982, was among the first commercial aircraft to feature a fully integrated FMS. Since then, the system has evolved from a dedicated navigation computer into a comprehensive flight management hub that touches fuel planning, performance optimization, air traffic control datalink (ACARS), and cabin systems integration. Today, every transport-category jet aircraft is required to carry an FMS or equivalent navigation management system for RNAV operations.

How It Works

At the core of an FMS is a flight management computer (FMC) — typically a pair of redundant units operating in hot standby mode. The crew enters the route via the Control Display Unit (CDU), a keyboard-and-screen interface mounted on the center pedestal. The FMC then computes the lateral flight plan (LNAV) as a series of connected waypoints and airways, and the vertical profile (VNAV) specifying altitude constraints, speed targets, and top-of-descent point.

During flight, the FMS continuously cross-checks position estimates from GPS, IRS, and radio navaid updates (VOR/DME ranging). It then feeds steering commands to the flight director and autopilot for seamless hands-off navigation. The performance management function uses a stored aerodynamic model of the specific aircraft to compute optimum cruise altitudes (step climbs), cost-index-based speed schedules, and continuous descent approaches (CDA) that minimize noise and fuel burn over populated areas.

Key Components

• Flight Management Computer (FMC): Dual or triple redundant processing units housing the navigation database (updated every 28 days via AIRAC cycles), performance database, and trajectory computation algorithms.
• Control Display Unit (CDU): Alphanumeric keyboard and multi-line display used by pilots to enter routes, performance data, and review FMS pages. On newer aircraft the CDU may be replaced by a touchscreen multifunction control display unit (MCDU).
• Navigation Database: Stores all airways, waypoints, procedures (SIDs, STARs, approaches), and airport data worldwide. Refreshed on a 28-day AIRAC cycle per ICAO standards.
• Performance Database: Aircraft-specific aerodynamic and engine performance model used to compute optimal speeds, altitudes, and fuel predictions.
• Data Bus Interface: ARINC 429 or ARINC 629 buses connect the FMS to the autopilot, autothrottle, displays, and other avionics systems.

Aircraft Applications

• Boeing 737-800: Honeywell or Smiths (now GE) FMC paired with a CDU on the center pedestal, driving the EFIS navigation display and autopilot for full RNAV/RNP capability.
• Airbus A320-200: Thales or Honeywell FMGC (Flight Management & Guidance Computer) integrated with the fly-by-wire flight control laws, providing LNAV/VNAV and managed speed modes.
• Boeing 777-300ER: Honeywell FMC with Airplane Information Management System (AIMS) integration, enabling dual FMS operation with crew alerting on a common computing platform.
• Boeing 787-9: Honeywell FMC embedded within the Common Core System, offering continuous GPS/IRS blending and advanced Required Navigation Performance (RNP AR) approaches down to 0.1 nm accuracy.
• Airbus A350-900: Thales FMGC with integrated datalink, supporting real-time weather uplink, oceanic clearance requests, and trajectory negotiation with ATC via CPDLC.

Advantages and Limitations

The FMS reduces crew workload substantially by automating route following, speed management, and fuel monitoring. Fuel savings of 3–5% are typical compared to manual navigation, with additional savings from CDA profiles. RNP AR capability unlocks curved approaches into terrain-constrained airports such as Kathmandu and Queenstown, previously inaccessible to jets.

Limitations include dependence on an up-to-date navigation database — an expired database renders many procedures unavailable. Complex route amendments in high-workload phases can distract crews; this "head-down" time has been identified as a contributing factor in several incidents. Modern FMS designs mitigate this by enabling ACARS datalink route uploads from dispatch, reducing manual CDU entry. Additionally, FMS trajectory predictions assume nominal winds and temperatures; significant deviations require manual intervention or updated uplinks.