Flight Management System — Page 279, Lesson 324

Let’s start with the Flight Management System, and I want to walk you through the two data bases that make the whole thing work, because everything else in the FMS hangs off them. First, the performance data base. Its purpose is to reduce the need for the flight crew to refer to the Cruise Control Manual during flight, and to provide the FMC — that’s the Flight Management Computer — with the information it needs to calculate pitch and thrust commands. So think of it this way: the performance data base is what lets the FMC figure out how to fly the aircraft efficiently. All the reference data you would normally need can be displayed on the FMS-CDU, the Control Display Unit. The data stored in that data base includes aircraft drag and engine characteristics, and maximum and minimum speeds. And here’s a nice detail: maintenance can refine the data base for each individual aircraft by entering factors for drag and fuel flow — so the performance model gets tuned to that specific airframe. Now the second one, the FMC navigation data base. This includes most of the information you would normally get by referring to navigation charts. That information can be displayed on the FMS-CDU / AMD — AMD being the associated display — and it eliminates most of the cockpit chart reading in aircraft without an FMC. The geographic area covered includes all areas where the aircraft is normally flown. The stored information includes the location of navigation aids, airports, runways, and other airline-selected information such as SIDs, STARs, approaches, and company routes. SIDs are Standard Instrument Departures, STARs are Standard Terminal Arrival Routes. Now here’s a critical operational point about the navigation data base. The FMC contains two sets of navigation data, each valid for 28 days. Each set corresponds to the normal revision cycle for navigation charts. During preflight, the flight crew can select which set is active, and the FMC uses the active set for all its navigation calculations. The contents are updated by maintenance every 28 days. So when the navigation chart revision date arrives, the new data is already in the FMC and ready for selection — you don’t have to wait for it to load. Then we move into Operational Procedures — Initial Actions, starting with the IDENT page. Upon application of power to the aircraft, the FMS immediately executes a self-test procedure. Upon its successful self-completion, the IDENT page of the system is displayed. The IDENT page of the FMC allows the crew to confirm — and that’s where the excerpt cuts off, but that’s the point: it’s the page that lets you verify what software and data base versions are loaded before you go any further. So to tie it together: performance data base feeds the FMC’s pitch and thrust calculations, navigation data base feeds its position and routing, and the IDENT page is your first confirmation step on the ground.