Electronic Instrumentation — Page 552, Lesson 656

Let's start with the standby engine indicator, because it's a small but important piece of the puzzle. This indicator provides primary engine information in the event that a total loss of EICAS displays occurs. So, EICAS is your main engine indication system, and if that completely fails, you still need to know what your engines are doing. That's exactly what this standby unit is for. As shown in Figure 39.7, the information it gives you relates to N1 and N2 speeds and EGT. N1 is the low-pressure compressor speed, N2 is the high-pressure compressor speed, and EGT is the exhaust gas temperature. The displays are of the LCD type, meaning liquid crystal display. And importantly, operating limit values are also displayed, so you can see your actual readings against the limits. Now, let's move to the Electronic Centralized Aircraft Monitoring system, or ECAM. This system was originally developed for the Airbus A310, and the units comprising it are shown in the functional diagram of Figure 39.8. Here's the key difference between ECAM and EICAS. As far as the processing and display of information are concerned, ECAM differs significantly from EICAS. With EICAS, the data relates primarily to engine and aircraft systems. But with ECAM, the data relates essentially to the primary systems of the aircraft, and it's displayed in check-list and pictorial or synoptic format. So instead of just raw numbers, you get a checklist and a picture of the system. Engine operating data is still displayed by conventional types of instruments, as noted in the introduction to this chapter. Other differences relate to display locations and selection of system operating modes. Let's look at the display units. These units may be mounted side-by-side. The left-hand unit is dedicated to information on the status of systems, warnings, and corrective action in a sequenced check-list format. So if something goes wrong, the left screen gives you a step-by-step list of what to do. The right-hand unit is dedicated to associated information in pictorial or synoptic format. That's the schematic picture of the system, so you can see what's happening visually. Now, the display modes. There are four display modes. Three of them are automatically selected, and they are referred to as: Flight Phase-related, Advisory (mode and status), and Failure-related modes. The fourth mode is manual, and that's the Aircraft System Display. Let's go through the automatic ones. The Flight Phase-related Mode is used in normal operation. In this case, the displays are appropriate to the current phase of aircraft operation, i.e. preflight, take-off, climb, cruise, descent, approach, and after landing. So the screen changes automatically depending on what phase of flight you're in. An example of a preflight phase is shown in Figure 39.9. The left-hand display unit displays an advisory memo mode, and the right-hand unit displays a diagram of the aircraft's fuselage, doors, and arming of the escape slides deployment system. So during preflight, you can see the doors and whether the escape slides are armed. Next is the Advisory mode, which includes mode and status. Status messages, which are also displayed on the left-hand display unit, provide the flight crew with an operational summary of the aircraft's condition. This includes possible downgrading of autoland capability, and as far as possible, indications of the aircraft status following all failures except those that do not affect the flight. So it tells you the overall health of the aircraft, and whether your autoland capability has been downgraded. The contents of an example display are shown in Figure 39.10. Finally, the Failure-related Mode. This mode takes precedence over the other two automatic modes and the manual mode. So if there's a failure, this mode overrides everything else to show you what's wrong. An example of a display associated with this mode is shown in Figure 39.11. So to summarize the hierarchy: in normal operation you get the flight phase-related mode. If there's a status message, you get the advisory mode. But if there's a failure, the failure-related mode takes precedence over both of them and the manual mode. That's the ECAM system in a nutshell.