Let's pick this up right where the FMC has just finished its power-up… — Page 279, Lesson 325

Let's pick this up right where the FMC has just finished its power-up self-test. When that test completes successfully, the system automatically displays the IDENT page. That's our very first screen, and it's the crew's confirmation point on start-up. On the IDENT page, we confirm the aircraft details. This isn't just a formality — confirming this page initiates a series of prompts that will direct us through the route procedures we need to generate for the flight. So think of it as the gateway that starts the whole route-building sequence. Two critical things live on this page. First, confirmation of the navigation database in operation — which nav data programme is currently loaded and active. Second, an indication of the date of changeover to the next programme. That's the date when the new database becomes current. If our database is out of date, the system will tell us to change to the in-date programme. So we're checking that we're flying with current navigation data, not expired data. Once we've checked the IDENT page, we're directed to the POS INIT page. Here we must check the FMS clock time against the aircraft clock to ensure synchronization between the systems. Why does this matter? Because data is saved on the FDR — the Flight Data Recorder — against time. And ETAs, the Estimated Times of Arrival, are generated by the FMC and need to be in line with the times indicated by the aircraft clock. So if the clocks disagree, our recorded data and our ETAs are both compromised. While we're on POS INIT, we must also ensure the airfield datum or gate position is entered accurately, if it's available. This position allows for IRS alignment — that's the Inertial Reference System. This entered position is suitable for alignment, but it's often updated at the take-off point to obtain the best possible initial position for use in flight. So we use the gate position to get the IRS aligned, then refine it later for a better starting reference. After POS INIT, we're directed to the RTE page. Here we enter our starting and destination airport ICAO designators — those are the four-letter airport codes. We may then expect to enter our flight number details and identify a "standard" company route to take us to our destination. If a standard route is not available, other actions will have to be taken to input the information into the system. So the system prefers a pre-defined company route, but we have a fallback if none exists. Finally, we move to the PERF INIT page, where we update the aircraft to its current performance and weight configuration for the route to be flown. On this page we may input details of fuel weight, fuel reserves required, and cruise altitude. And in the case of the B747, we can even input if we're carrying a fifth engine to our destination upon its suspension point on the wing — that's the spare engine carried on the wing pylon. At this stage we may also enter Cost Index requirements related to our flight, which we'll discuss later in the chapter. So the sequence is: IDENT to confirm aircraft and nav database, POS INIT to synchronise clocks and set the alignment position, RTE to build the route, and PERF INIT to set performance and fuel. Each page hands off to the next, guiding us through the entire pre-flight setup.