Let's pick this up right where the scenario left off — Page 552, Lesson 658

Let's pick this up right where the scenario left off. We're taxiing out for take-off, and the temperature of the brake unit on the rear right wheel of the left main landing gear bogie has become excessive. That's a real problem, so let's see exactly how the system reacts and what the crew does about it. The moment that temperature exceeds its limit, the system springs into action. A diagram of the wheel brake system is immediately displayed on the right-hand display unit. At the very same time, the left-hand unit displays the corrective action the flight crew needs to take. So you have a split-screen response: the right side shows you what is wrong, the left side tells you what to do about it. But it doesn't stop there. In addition to those two visual displays, an aural warning is sounded — that's an audible alert so the crew notices even if they're not looking at the screens. And there's a light, placarded 'L/G WHEEL', on a central warning light display panel that illuminates. So you have three channels of warning: the right display, the left display, the sound, and the light. That's four, actually — visual on both screens, aural, and the dedicated light. Now, as the crew carries out the corrective action, something important happens. The instructions on the left-hand display are replaced by a message in white confirming the result of the action. So the left screen changes from "do this" to "done — here's the confirmation." Meanwhile, the diagram on the right-hand display unit is appropriately 'redrawn' — it updates to reflect the new state of the system. Here's a key convention to understand. In this example, the failure relates to a single system. By convention, such warnings are signified by underlining the system title displayed. So if you see an underlined title, that means the failure is contained to that one system. But what if a failure can affect other sub-systems? Then the title of the sub-system is shown 'boxed' — enclosed in a box, as you'd see in Figure 39.12. That's the visual cue that this failure has knock-on effects beyond just the one system. Underline means isolated; boxed means it spreads. Now, how do you clear all of this? Warnings and the associated lights are cleared by means of 'CLEAR' push-button switches. These are located on either the ECAM control panel or a warning light display panel. So the crew presses CLEAR to acknowledge and dismiss the warning. Let me pause there and make sure you've got the full picture of that warning sequence, because it's a classic exam scenario. Excessive brake temperature → right display shows the brake system diagram → left display shows corrective action → aural warning sounds → 'L/G WHEEL' light illuminates on the central panel → crew acts → left display confirms in white → right diagram redraws → crew presses CLEAR to dismiss. Now let's move on to the next part of the system — the Fourth Mode, called Manual, or the Aircraft System Display Mode. This mode is for routine checking, not for warnings. It permits the selection of diagrams related to any one of 12 of the aircraft's systems. So you can pull up a diagram of, say, the hydraulic system or the electrical system for a routine look. It also permits the selection of status messages — but only provided no warnings have been triggered for display. So if there's an active warning, you can't just browse status messages; the warning takes priority. The selections are made by means of illuminated push-button switches on the system control panel. So you press the button for the system you want to see, and it lights up to show it's selected. Now let's look at the ECAM Control Panel itself, shown in Figure 39.13. All the switches on it, with the exception of those for display control, are of the push-button, illuminated caption type. So they're buttons that light up to show their state. There are two types of switches I want to walk you through. First, the SGU Selector Switches. SGU stands for Symbol Generator Unit — that's the unit that generates the symbols and diagrams you see on the displays. These switches control the respective symbol generator units. In normal operation, the lights are off — that's the healthy state. But if a failure is detected by an SGU's internal self-test circuit, the 'FAULT' caption illuminates amber. So amber FAULT means that particular SGU has detected a problem in itself. Here's the action: releasing a switch isolates the corresponding SGU. When you release that switch, the 'FAULT' caption extinguishes — the amber light goes out — and the 'OFF' caption illuminates white. So you've taken that faulty SGU out of service, and the white OFF tells you it's now isolated. Second, the Synoptic Display Switches. These permit individual selection of synoptic diagrams corresponding to each of the 12 systems. They illuminate white when pressed, so you can see which one you've selected. And here's a critical safety feature: a display is automatically cancelled whenever a warning or advisory occurs. So if you're just browsing a synoptic diagram for routine checking and a warning comes up, your selection is cancelled automatically — the system takes priority and shows you the warning instead. Let me tie this together. The ECAM system has multiple modes. We've just covered the warning mode in the brake scenario, and now the Manual mode for routine checking. The key contrast is: warnings override everything, and the CLEAR button dismisses them. In Manual mode, you browse 12 systems freely, but any warning cancels your selection. One more thing to note on the SGU switches — the FAULT caption is amber, the OFF caption is white. Those colours matter. Amber is a caution, white is a status indication. And the Synoptic switches illuminate white when pressed. So white is your "selected" or "off" state, amber is your "fault" state. That's the full picture of this section. You've got the warning sequence, the underlining versus boxing convention, the CLEAR function, the Manual mode with its 12 systems, and the ECAM control panel with its SGU and Synoptic switches.