A Flight Management System, or FMS, is often called the brain of the modern cockpit because it helps organize navigation, performance, fuel planning, and guidance in one computer system. The pilot enters a flight plan, including departure, waypoints, airways, arrival, and runway information. The FMS then calculates a path for the aircraft to follow and shares that information with cockpit displays and the autopilot.
This matters because modern flights are too complex to manage efficiently with hand calculations alone.
Key Facts
- The FMS stores the flight plan as a sequence of waypoints, airways, procedures, and altitude or speed constraints.
- Basic time estimate: time = distance / ground speed.
- Basic fuel estimate: fuel used = fuel flow rate x time.
- The FMS sends lateral navigation commands for route tracking and vertical navigation commands for climb, cruise, and descent planning.
- Inputs include pilot entries, GPS, inertial sensors, air data, radio navigation, engine data, and navigation databases.
- Outputs include cockpit map displays, guidance cues, autopilot commands, performance predictions, and fuel remaining estimates.
Vocabulary
- Flight Management System
- A cockpit computer system that plans, calculates, and guides the aircraft along a programmed route.
- Waypoint
- A named geographic position used as a navigation point along a flight route.
- Navigation Database
- A stored collection of airports, runways, waypoints, airways, and procedures used by the FMS.
- Autopilot
- A system that can control the aircraft's flight path using guidance commands from systems such as the FMS.
- VNAV
- Vertical Navigation is an FMS function that helps manage altitude, climb, descent, and speed targets.
Common Mistakes to Avoid
- Thinking the FMS flies the airplane by itself is wrong because it computes guidance, but the autopilot or pilot must actually control the aircraft.
- Entering a waypoint incorrectly is wrong because one wrong letter or selection can send the aircraft toward the wrong fix or procedure.
- Trusting fuel predictions without checking conditions is wrong because winds, altitude changes, holding, and routing changes can affect actual fuel use.
- Assuming the navigation database is always current is wrong because expired databases may contain outdated procedures, runways, or waypoint information.
Practice Questions
- 1 An aircraft flies a 420 nautical mile leg with a ground speed of 280 knots. How long will the leg take in hours and minutes?
- 2 An aircraft burns 2,400 kg of fuel per hour during cruise. If the FMS predicts 1.75 hours of cruise, how much fuel will be used?
- 3 A pilot enters the route correctly, but the aircraft is not following it because the autopilot is in heading mode instead of navigation mode. Explain why the FMS flight plan alone does not guarantee the aircraft will track the route.