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I'm looking at a picture of the electrical panel of a Phenom 100 and on it I see a + sign, does anyone have any ideas as to what it's supposed to mean?

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Bobby Tables
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1 Answers1

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enter image description here
(airliners.net)

Above I marked five similar plus signs on the 737 (there are more). Beneath the +'s are the contacts for the backlighting of each panel. If it acts up then pressing on the sign will ground/secure the connection and may solve the issue.

The electroluminescent light-panels are flexible and the ride can be too bumpy sometimes. Better push the right spot than wait for a specialized someone on the ground who knows where each contact is.

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Composite based on images from b737.org.uk.

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    I'm not sure if that's amazing or terrifying – Wayne Werner Sep 18 '17 at 11:37
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    Can you explain that more? Why would the backlight “act up” and why would pressing on the + symbols resolve it? – Michael Sep 18 '17 at 13:37
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    I'm more of an electronics person than aviation, but I wonder if "backlighting" should be "backplane"? That would seem to make more sense in terms of securing it more firmly to the connectors on the backplane that would be underneath. – PeterJ Sep 18 '17 at 13:38
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    That's it, I'm taking the train next time! – dotancohen Sep 18 '17 at 13:41
  • That's really interesting they've chosen that term when it has a different meaning in electrical engineering. But your edit make it much clearer it's just pressing in a contact so +1. – PeterJ Sep 18 '17 at 14:12
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    @Michael They're specifically on 'light plate' panels that contain the backlights for any markings required. The lights in these panels are powered via (sprung?) contacts touching below the mark rather than anything more positive, so they indicate where to apply pressure to flex the panel if it's not making good contact. – Gwyn Evans Sep 18 '17 at 18:53
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    I find it amazing that with all the safety regulations, certifications, etc that they would or even could design a panel where the backlights might flicker out and require the pilot to push on the panel to reconnect them! That's just... really??? – FreeMan Sep 19 '17 at 11:36
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    @ymb1 - not to drag this too far off topic, but I'm amazed that the panels are built in a way that would allow the contacts to "bump loose" due to some turbulence in the first place. Everything else is built with triple redundancy, but my dashboard lights can flicker out at any time? Especially a potentially high stress time like turbulence? – FreeMan Sep 19 '17 at 12:00
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    Is there a little mark on the fuel gauge, too, to indicate where I should tap in case the indicated value is too low? – Pavel Sep 19 '17 at 12:19
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    To those wondering about design and redundancy, the electroluminescent backlighting is hardly a critical system. That being said, the panel floodlights are the primary redundancy, the requisite D-Cell flashlight is the secondary redundancy, and my pocket flashlight is the tertiary redundancy. – J W Sep 19 '17 at 20:26
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    So this is an example of where "percussive maintenance" can actually be effective. – Dan Henderson Sep 19 '17 at 22:10
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    Why is the positive sign used for grounding the plate? – dotancohen Sep 20 '17 at 12:30
  • There's a minor inaccuracy here. The purpose of the + is not when the panel "bumps loose". What they're supposed to be used for is when reinstalling the panel, before the screws are fully tightened, the mechanic applies pressure to the +. This aligns the panel with the contacts, then the screws are tightened to hold it in place. Pilots banging on the + is an unofficial field-expedient fix, particularly if the previous mechanic was lazy and didn't install it properly. – user71659 Feb 07 '23 at 20:05