A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry flight engineers or navigators. A primary function is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the cockpit, the FMS is normally controlled through a Control Display Unit (CDU) which incorporates a small screen and keyboard or touchscreen. The FMS sends the flight plan for display to the Electronic Flight Instrument System (EFIS), Navigation Display (ND), or Multifunction Display (MFD). The FMS can be summarised as being a dual system consisting of the Flight Management Computer (FMC), CDU and a cross talk bus.
The modern FMS was introduced on the Boeing 767, though earlier navigation computers did exist. Now, systems similar to FMS exist on aircraft as small as the Cessna 182. In its evolution an FMS has had many different sizes, capabilities and controls. However certain characteristics are common to all FMSs.
Navigation database
All FMSs contain a navigation database. The navigation database contains the elements from which the flight plan is constructed. These are defined via the ARINC 424 standard. The navigation database (NDB) is normally updated every 28 days, in order to ensure that its contents are current. Each FMS contains only a subset of the ARINC / AIRAC data, relevant to the capabilities of the FMS.
The NDB contains all of the information required for building a flight plan, consisting of: Waypoints/Intersection Airways Radio navigation aids including distance measuring equipment (DME), VHF omnidirectional range (VOR), non-directional beacons (NDBs) and instrument landing systems (ILSs). Airports Runways Standard instrument departure (SID) Standard terminal arrival (STAR) Holding patterns (only as part of IAPs-although can be entered by command of ATC or at pilot's discretion) Instrument approach procedure (IAP)
Waypoints can also be defined by the pilot(s) along the route or by reference to other waypoints with entry of a place in the form of a waypoint (e.g. a VOR, NDB, ILS, airport or waypoint/intersection).
Flight plan
The flight plan is generally determined on the ground, before departure either by the pilot for smaller aircraft or a professional dispatcher for airliners. It is entered into the FMS either by typing it in, selecting it from a saved library of common routes (Company Routes) or via an ACARS datalink with the airline dispatch center.
During preflight, other information relevant to managing the flight plan is entered. This can include performance information such as gross weight, fuel weight and center of gravity. It will include altitudes including the initial cruise altitude. For aircraft that do not have a GPS, the initial position is also required.
The pilot uses the FMS to modify the flight plan in flight for a variety of reasons. Significant engineering design minimizes the keystrokes in order to minimize pilot workload in flight and eliminate any confusing information (Hazardously Misleading Information). The FMS also sends the flight plan information for display on the Navigation Display (ND) of the flight deck instruments Electronic Flight Instrument System (EFIS). The flight plan generally appears as a magenta line, with other airports, radio aids and waypoints displayed.
Special flight plans, often for tactical requirements including search patterns, rendezvous, in-flight refueling tanker orbits, calculated air release points (CARP) for accurate parachute jumps are just a few of the special flight plans some FMSs can calculate.