Electronic Instrumentation — Page 552, Lesson 656

I want to walk you through the standby engine indicator first, because it's a small but vital piece of the electronic instrumentation picture. This indicator provides primary engine information in the event that a total loss of EICAS displays occurs. Now, EICAS stands for Engine Indication and Crew Alerting System — that's the main electronic display system that normally shows you your engine data. So if that entire system goes dark, this standby unit is your backup. As shown in Figure 39.7, the information it gives you relates to N1 and N2 speeds and EGT. Let me define those terms precisely. N1 is the low-pressure compressor speed, and N2 is the high-pressure compressor speed — these are the two spool speeds of a modern turbofan engine. EGT is Exhaust Gas Temperature, which tells you the temperature of the gases leaving the engine. The displays on this standby indicator are of the LCD type — that's Liquid Crystal Display. And importantly, operating limit values are also displayed, so you can see not just the current readings but the limits you must not exceed. Now let's move to the ECAM system — that's Electronic Centralized Aircraft Monitoring. 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 point: as far as the processing and display of information are concerned, the ECAM system differs significantly from EICAS. The data in ECAM relates essentially to the primary systems of the aircraft — that's the core difference. And this data is displayed in check-list and pictorial or synoptic format. Let me explain that. A synoptic format is a schematic diagram — a simplified pictorial representation of a system, like a hydraulic or electrical system, showing how its components connect. So instead of just numbers, you get a picture of the system. Engine operating data, however, is 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 walks you through a checklist in order — here's the warning, here's what you do about it. The right-hand unit is dedicated to associated information in pictorial or synoptic format — the schematic picture of the affected system. So the left gives you the words and the sequence, the right gives you the picture. Now the display modes. There are four display modes, three of which are automatically selected. Those three are: Flight Phase-related, Advisory (which covers mode and status), and Failure-related modes. The fourth mode is manual, and it's called the Aircraft System Display. So you have three automatic modes and one manual mode. Let me take you through the Flight Phase-related Mode first. In normal operation, the automatic flight phase-related mode is used. In this case, the displays are appropriate to the current phase of aircraft operation — that is, preflight, take-off, climb, cruise, descent, approach, and after landing. So the system knows what phase of flight you're in and shows you what's relevant for that phase. An example of a preflight phase is shown in Figure 39.9. In that example, 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're checking the doors and the escape slides are armed. Next is the Advisory mode, covering 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. They also give you possible downgrading of autoland capability — that's important, because autoland is the system that lets the aircraft land automatically in low visibility, and if something's degraded, you need to know your autoland capability is reduced. And as far as possible, these status messages give indications of the aircraft status following all failures, except those that do not affect the flight. So if a failure doesn't affect the flight, it won't show up here. 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 a failure occurs, the failure-related mode overrides everything else — it takes priority over the flight phase-related mode, the advisory mode, and the manual aircraft system display. An example of a display associated with this mode is shown in Figure 39.11. So to tie it all together: ECAM gives you a centralized, phase-aware picture of your primary systems, with the left screen for checklists and status, the right screen for synoptic pictures, and a failure mode that always takes priority when something goes wrong.