Area Navigation Systems (RNAV) — Page 276, Lesson 267

Let’s start with the Control and Display Unit, the CDU. This is the pilot’s interface with the Flight Management Computer, the FMC. Think of the CDU as the keyboard and screen you use to talk to the FMC, and the FMC as the brain that does the navigation and performance calculations. The CDU is used before flight to initialize the performance and navigation requirements for the flight. So you set up the aircraft’s performance data and the navigation plan through this unit before you even start moving. Now, look at the layout. Alongside the display you have the alphanumeric keypad — that’s the letters A through Z and the numbers 0 through 9, plus the decimal point and the plus/minus key. You also have specific function keys. Let me name the ones you see here: INIT, REF, RTE, CLB, CRZ, DES, DIR, INTC, LEGS, DEP, ARR, EXEC, PROG, NAV, RAD, PREV PAGE, NEXT PAGE, and MENU. Each of these calls up a specific function page on the display. But the key feature I want you to focus on is the line select keys, abbreviated LSK. These are the keys positioned alongside the display, one for each line of data shown. The LSKs are used for inserting or selecting data into the FMC and for moving through the various function pages. So when you see a data field on the screen, you press the LSK next to it to select that field or to enter data into it. Now let’s talk about the display format, because you need to read this correctly. In the top field of the display is the title of the selected page. And where the selected function has more than one page, you’ll also see the page number — for example, “1 of 3.” That tells you you’re on the first of three pages for that function. In the centre of the display are up to 10 data fields — 5 on the left and 5 on the right. These are the fields you access using the LSKs. Each of those 10 fields can hold data that you either read or modify. At the bottom of the screen are two or more page select fields. These let you move between the pages of a function. And below them is the scratchpad. The scratchpad is used to input or modify data for insertion into the appropriate data field. So you type your data into the scratchpad first, then use the LSK to insert it into the correct field on the page. Let me show you what this looks like. That’s Figure 16.6, the control and display unit. You can see the page title at the top, the data fields in the centre, the page select fields at the bottom, and the scratchpad below them. Now let’s move to the pre-flight phase. The pre-flight initialization of the FMC in the navigation mode requires the pilot to check the validity of the database and input several items. First, you check that the correct database is installed. This is done on the IDENT page. The database contains the navigation data — waypoints, airways, airports — and you must verify it’s the right one and that it’s valid for the flight. Second, you input the aircraft position. This is done on the POS INIT page. The position initialization page allows you to initialize the heading and position for the FMC. Third, you input the departure and destination aerodromes — where you’re leaving from and where you’re going to. Fourth, you input the intended SID and STAR procedures. SID stands for Standard Instrument Departure, and STAR stands for Standard Terminal Arrival Route. These are the published departure and arrival procedures you’ll fly. And fifth, you input the planned route — again on the POS INIT page. Let me show you the position initialization page. That’s Figure 16.8, the POS INIT page. This is where you initialize the heading and position for the FMC. So to summarise the pre-flight sequence: you check the database on IDENT, then on POS INIT you input the aircraft position and the planned route, and you also input the departure and destination aerodromes and the SID and STAR procedures. One more thing to note — the FMC runs an internal test sequence when power is applied. That’s Figure 16.7. When power is applied, the FMS executes an internal test sequence. When the test is successfully completed, the system is ready for initialization. So the key terms here: CDU is the control and display unit, FMC is the flight management computer, LSK is the line select key, and the scratchpad is where you type data before inserting it into a field. The display has a page title at the top, up to 10 data fields in the centre, page select fields at the bottom, and the scratchpad below them. And pre-flight, you check the database on IDENT, input position and route on POS INIT, and input the departure and destination aerodromes plus the SID and STAR procedures.