Inertial Navigation Systems — Page 244, Lesson 287

Right, let's get into the Inertial Navigation System panel. I want to walk you through the actual cockpit unit, because for the exam you need to know what every display and control does, not just the theory of how the gyros work. First, a quick word on the panel itself. The one we're looking at is just an example. Other INS panels may look dissimilar to the one shown at Figure 18.17, but the information given by the system will be basically the same. So learn the functions, not the exact layout. Let's start at the top left-hand corner. The two large windows at the top of the panel are labelled the left and right numerical displays. These are the principal outputs of the system — this is where the system gives you its main answers. Now, glance down to the bottom left-hand corner. That's the function selector. We'll start with the selector in the seven o'clock position, which is the TK/GS position, and work anticlockwise through the functions, considering the values shown in the two LED windows as we go. So TK/GS is your starting point — that stands for track and groundspeed. As you rotate the selector anticlockwise, you'll step through the other functions, and the two LED windows will show the corresponding values for each function. Next, the waypoint selector switch. This is a thumbwheel. You thumb it to the appropriate waypoint number, and that number is shown in the window to the left of the thumbwheel. You use this when loading the waypoint lat/longs before flight, when reloading new waypoints in flight, or when checking that waypoints are correctly loaded. Now, the FROM/TO waypoint display. This shows the two waypoints between which the INS assumes that it is flying. And here's the critical point: all digital read-outs, flight director displays, and autopilot commands will be based on this information. So you can imagine the consequences of either giving the equipment the wrong to/from waypoint numbers, or feeding the system with the wrong waypoint lat/long to begin with. Everything downstream — the flight director, the autopilot — trusts this. Then we have the track change push-button. This enables the operator to tell the system between which two waypoints the aircraft is required to fly, in the event that the system is not set up to fly sequentially through the loaded waypoints. So normally it flies them in order, but if you want to skip or jump, you use this button to specify the pair. Finally, the DIM control. That governs the brightness of the LED displays and the panel lighting. So, to tie it together: the two big windows are your outputs, the function selector chooses what those windows show, the waypoint selector loads and checks your waypoints, the FROM/TO display tells you which leg the system thinks it's on, the track change button lets you override the sequence, and the DIM control handles brightness. That's the whole panel, top to bottom, left to right.