Electronic Instrumentation — Page 546, Lesson 649

We're starting a new topic now: Electronic Instrumentation, and specifically the EICAS system. Let's get into it. EICAS stands for Engine Indication and Crew Alerting System. It's the system that takes all the engine data and the aircraft's alerting functions and puts them together on electronic displays. The key idea here is that EICAS is designed to categorize its displays and alerts according to function and usage. To do that, it has three distinct modes of displaying information: operational, status, and maintenance. Let me walk you through each mode. The operational mode and the status mode are selected by the flight crew on the display select panel. The maintenance mode, however, is selected on the maintenance panel, which is for the use of ground engineering staff only. So right away, you see a division: two modes for the pilots, one for the engineers. 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 in this mode. The lower display unit remains blank, and it can be selected to display secondary information as and when required. So in normal cruise, you're mostly looking at the upper screen for your primary engine data. The status mode is different. When selected, it displays data to determine the dispatch readiness of an aircraft. This is closely associated with the details contained in an aircraft's Minimum Equipment List, or MEL. The MEL tells you what equipment can be inoperative and still allow the aircraft to be dispatched. The status display shows the positions of the flight control surfaces in the form of pointers registered against vertical scales. It also shows selected sub-system parameters, and equipment status messages, all on the lower display unit. Selection of this mode is normally done on the ground, either as part of preflight checks of dispatch items, or prior to shut-down of electrical power. The purpose there is to aid the flight crew in making entries in the aircraft's Technical Log. Now the maintenance mode. This provides maintenance engineers with information in five different display formats to aid them in trouble-shooting and verification testing of the major sub-systems. These displays are presented on the lower display unit, and importantly, they are not available in flight. So this is purely a ground function for the engineers. Let's look at the display select panel itself. This panel permits control of EICAS functions and displays, and it can be used both in flight and on the ground. It's normally located on the centre pedestal of the aircraft's flight deck. It has three controls. First, the Engine Display Switch. This is of the momentary-push type, used for removing or presenting the display of secondary information on the lower display unit. Second, the Status Display Switch. Also momentary-push, this is used to display the status mode information on the lower display unit. That display is known as a 'status page'. 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 the APU — that's the Auxiliary Power Unit. Here's the important part about event recording. Normally, if any malfunction occurs in a system, it is recorded automatically. That's called an 'auto event', and it's stored in a non-volatile memory of the EICAS computer. Non-volatile means the data is retained even when power is removed. The push-switch also enables the flight crew to record a suspected malfunction for storage, and that's called a 'manual event'. So you have auto events and manual events. The relevant data can only be retrieved from memory and displayed when the aircraft is on the ground, and only by operating switches on the maintenance control panel. So the crew can record events in flight, but only the engineers on the ground can pull that data back out. So to tie it together: operational mode for in-flight engine data and alerts, status mode for dispatch readiness on the ground, and maintenance mode for the engineers. The display select panel gives the crew control over the first two, and the event record switch lets them capture fault data for later analysis.