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Does the master caution light illuminate only with the System Annunciator Panel? Or is the master caution illumination also connected to the related system panels?

I mean if there is an indication on a system panel and the System Annunciator Panel is inop due to some issue, does the master caution illuminate alone?

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If everything is working as designed then the Master Caution is always accompanied by one of the 12 annunciator lights (or more than 1, depending on the situation).

If things aren't working as designed, then what you'll see depends on the nature of the malfunction. If it's as simple as a burned-out bulb in the annunciator panel, then you could get the Master Caution without an accompanying light. That's usually followed by a disgruntled "oh, great" followed by heads swiveling around to find what individual amber light is illuminated. And/or pressing the Recall function (see what fails to light up, or comes on now), and/or using the Lights Test switch.

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  • $\begingroup$ In the event of a bulb burning out (who is still using incandescents in safety-critical hardware?!) wouldn't the problem also be displayed on one of the MFDs? $\endgroup$ – Dai Nov 9 '20 at 23:34
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    $\begingroup$ @Dai: Incandescent bulbs can be quite reliable if they are used significantly below their maximum power rating. LEDs are claimed to last longer, but I've seen plenty of LED assemblies with failed LEDs in them. $\endgroup$ – supercat Nov 10 '20 at 2:30
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    $\begingroup$ The 737 cockpit still uses the same 386 bulbs in the caution lights that the original ones did decades ago. And no, even the Max still doesn't have an EICAS. $\endgroup$ – Ralph J Nov 10 '20 at 2:30

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