Electronic Instrumentation — Page 552, Lesson 660

I want to walk you through the ECAM control panel and how its switches work, because this is the crew's interface for managing the warning and status messages that the system generates. We're looking at three switches here: the CLR switch, the STS switch, and the RCL switch. Let's start with the CLR switch. The light inside this switch is illuminated white whenever a warning or status message is displayed on the left-hand display unit. So the white light tells you something is currently being shown. Pressing the switch clears those messages from the display. Next is the STS switch, which stands for Status. This switch permits manual selection of an aircraft status message if no warning is displayed. Its light is also illuminated white. When you press the STS switch, it also causes the CLR switch light to illuminate. Now here's an important limitation: a status message is suppressed if a warning occurs, or if the CLR switch is pressed. So the status message only stays up under the right conditions. Then we have the RCL switch, the Recall switch. This enables previously cleared warning messages to be recalled, but only provided the failure conditions which initiated them still exist. Pressing RCL also causes the CLR switch light to illuminate. And here's the key contrast: if a failure no longer exists, the message 'NO WARNING PRESENT' is displayed on the left-hand display unit. So the system tells you explicitly when there's nothing to recall. Now, let's connect this to the broader ECAM concept. The excerpt also touches on how the system behaves. With an Electronic Centralized Aircraft Monitoring type of system, the left display unit shows warning and corrective action in a check list format. That's the key point — the left unit is your checklist display. And for the Engine Indicating and Crew Alerting System, which is EICAS, alert messages appear on the upper display unit in three forms. Level 'C' are warnings that require immediate corrective action. Level 'A' are cautions that require immediate crew awareness and possible action. Level 'B' are advisories requiring crew awareness. And these messages appear on the top left of the upper display unit. So to tie it together: the CLR, STS, and RCL switches on the ECAM control panel manage what appears on the left display unit, and the alert levels A, B, and C tell you how urgently you need to respond. The white illumination on the switches is your cue that a message is active, and the system suppresses or recalls messages based on whether the failure condition still exists.