The Flight Management System is a dual redundant system that is fully integrated with the flight control system, the flight deck displays, and most of the aircraft sensor systems to provide information for continuous automatic navigation, guidance, and performance management.
The FMC and MCDU together provide the means for creating, modifying, and selecting four-dimensional (time is a waypoint parameter) flight plans. The FMC interfaces with the autopilot to provide Lateral Navigation (LNAV), Vertical Navigation (VNAV), and autothrottle commands to allow automatic flight control of the aircraft according to the selected flight plan.
The FMS has two basic modes of operation; Enroute and Tactical.  The Enroute Mode includes an outbound climb (CLB), cruise (CRZ), and decent (DES) from the origin to the tactical or task area, and an inbound CLB, CRZ, and DES from the task area to the destination airfield (or an alternate destination as required).  While operating in the Enroute Mode, the FMS provides both VNAV and LNAV guidance and steering.  At a designated point (normally in the outbound route) at or near the On-Task waypoint, the  crew switches to Tactical Mode.  During the Tactical Mode VNAV is disengaged.  The LNAV steering ignores waypoints in the flight plan, steering the aircraft to Fly-to-Points received from the Tactical Command System (TCS).  LNAV steering is also modified to account for the more demanding tactical flight requirements.  Performance advisories are provided to include Fuel Plan/Forecasts and remaining Time-on-Task, as required for operation in the Tactical Mode.

Flight Management Computer (FMC)

• Power PC Processor

• 7” H x 7” W x 11” D

• Weight 22 lbs

• Cooling – free convention

Multipurpose Control Display Units (MCDU)

• Full Color AMLCD display

• Reverse video highlighting

• Height 7 1/8 inches

• Weight 7 lbs

• ARINC 739 compatible user ports