Electronic Instrumentation — Page 546, Lesson 649

I want to walk you through the EICAS display modes and the display select panel. This is the heart of how the crew and ground engineers interact with the engine and aircraft systems information. First, the core idea: EICAS is designed to categorize displays and alerts according to function and usage. For that purpose, there are three modes of displaying information: operational, status, and maintenance. Let me define each mode precisely. The operational mode displays the engine operating information and any alerts that require action by the crew in flight. Normally, only the upper display unit presents information; the lower one remains blank and can be selected to display secondary information as and when required. The status mode, when selected, displays data to determine the dispatch readiness of an aircraft. It's closely associated with details contained in an aircraft's Minimum Equipment List — that's the MEL, the list of equipment that must be operative for the aircraft to be dispatched. The display shows positions of the flight control surfaces in the form of pointers registered against vertical scales, selected sub-system parameters, and equipment status messages on the lower display unit. Selection is normally done on the ground, either as part of preflight checks of dispatch items, or prior to shut-down of electrical power, to aid the flight crew in making entries in the aircraft's Technical Log. The maintenance mode provides maintenance engineers with information in five different display formats to aid them in trouble-shooting and verification testing of the major sub-systems. The displays are presented on the lower display unit and are not available in flight. Now, who selects which mode? Modes (i) and (ii) — operational and status — are selected by the flight crew on the display select panel. Mode (iii), maintenance, is selected on the maintenance panel, which is for the use of ground engineering staff only. Let's look at the display select panel itself. As indicated in Figure 39.3, this panel permits control of EICAS functions and displays and can be used both in flight and on the ground. It's normally located on the centre pedestal of an aircraft's flight deck. Its controls are as follows. First, the Engine Display Switch. This is of the momentary-push type, for removing or presenting the display of secondary information on the lower display unit. Momentary-push means you press it and it acts while pressed or toggles on that action. Second, the Status Display Switch. Also of the momentary-push type, this is used to display the status mode information I mentioned earlier, on the lower display unit. The display is known as a 'status page', an example of which is shown in Figure 39.4. Third, the Event Record Switch. Also momentary-push, used in the air or on the ground, to activate the recording of fault data relevant to the environment control system, electrical power, hydraulic system, performance, and APU — that's the Auxiliary Power Unit. Normally, if any malfunction occurs in a system, it's recorded automatically — this is called an 'auto event' — and stored in a non-volatile memory of the EICAS computer. The push-switch also enables the flight crew to record a suspected malfunction for storage, and this is called a 'manual event'. The relevant data can only be retrieved from memory and displayed when the aircraft is on the ground, and by operating switches on the maintenance control panel. So the key contrast here: auto events happen automatically on malfunction; manual events are crew-initiated via the Event Record Switch. And neither can be retrieved in flight — only on the ground, through the maintenance control panel. Let me show you the functional diagram so you can see how these pieces connect. And here's the engine data display and the status page example. That's the complete picture of the three modes and the display select panel controls.