Small crosses drawn all over cockpit panels

[littlejet]

Does anybody know what is the purpose of a small cross drawn on every part of the overhead and center panels. Seems that every system section of the panel has one.
I saw it on the B727 and B744.

Thnx

[BOAC]

Believed to be where to 'push' if there is a breakdown in panel background lighting as I understand the central circuit board component for the lighting is behind the cross. Based on an 'old-wives' tale' (old Captain, actually:))

[slowto280]

You say 'every part', this would be in just one corner. I know in some of the older types (other than 72 and 74, not familiar...) DC-8, L-188 and I think 707, these were places on the panel that were connected to the electrical system to power the panel lights. Quite often if the entire panel (panel, not instrument or guage...) background lights were not lit, pressing in that area would 'reconnect the panel', getting the lights back. Perhaps this....... :ouch:

[bbthefe]

I think it indicates there is a CB behind that panel ......
I'll try and check this week.;)

[DiamondRider]

As mentioned earlier this is an indication of where the panel/lightplate is electrically connected to the aircraft.

Underneath that cross there is a small electrical "connector" that fits in to a receptacle on the aircraft side.

[dixi188]

Usually a blue cross marks where the electrical connector is for the internal lighting. It is for the maintenance people to press when installing the panel to ensure the connection is made.

Whilst flight deck crew may find pressing here will restore lost lighting, this is not what you are supposed to do. I have seen people pushing, thumping, banging and then breaking things in an attempt to restore lost lighting or a failed instrument.

Write it up and let the maintenance people fix it.

Happy flying.

P.S. I work both sides of the fence.

[COF&COE]

On the 757/767 there is one of these small crosses on the MCP next to the Alt Selector. Training captains have been known to tell brand new F/O's that if they have to change the selected altitude for any reason, they must leave their finger on that cross until the Captain acknowledges it!:E

[rubik101]

It's where the panel is earthed to the airframe, as mentioned by DiamondRider.

[point8six]

Earthing points, according to a 747 Classic FE instructor (20+ yrs ago) oops there's another one!:E

[transducer]

A Dash-8 even has this cross on every panel. This is where the electrical connection for the back lighting makes contact. Sometimes the back lighting does not work an a particular panel and a gentle push on the cross usually solves the problem. You need a torch though to find the cross!

[NSEU]

"It's where the panel is earthed to the airframe,"

It's both power AND earth. The connection is a coaxial type arrangement, like you see on on some TV antenna cables.
If I remember correctly, there is a power pin in the middle and a circular earth (which may be divided into quadrants to allow expansion)... of course with a gap/insulation seperating them.

The control panel faceplates are usually painted clear plastic/perspex. On the back of the perspex is a printed circuit board with miniature lightbulbs attached to it. There is a single source of power for the circuit boards (i.e. behind the "+"). The clear perspex spreads out the light across the whole panel (refraction), so you don't need too many bulbs.

[Spanner Turner]

This question comes up fairly regularly, both at work and on pprune! Have a look at this previous thread for the same info but also with nice pictures.

http://www.pprune.org/tech-log/353840-767-panel.html

:ok:


.

[411A]

Circa 1991, L1011-500, with the digital display AP/FD glareshield panel.
The First Officer, new to the type, starts looking for the blue cross, due to one small section of the background panel lighting not illuminated.
Not finding the blue cross (they are there, but really hard to see) this 320 pound gorilla starts pushing with his big fat size 14 thumb, bent/cracked the electroluminicent panel, thereby rendering the nearby gas discharge displays inop.
Results?
New panel installed, to the tune of $126,000.

Said 320 pound gorilla was canned, forthwith.

Sometimes a bigger hammer is not the best way to proceed.

[V1... Ooops]

Here's the same two pictures that I posted to the above-referenced thread about the 767:

Below are two pictures showing the front and back of such a lighting panel (this one from a Twin Otter) - hopefully these photos will make it easier for you to visualize the concept explained by others, above.

http://dubfoto.com/albums/userpics/10003/Lighting_Panel_Front.jpg (http://dubfoto.com/displayimage.php?pos=-4078)

http://dubfoto.com/albums/userpics/10003/Lighting_Panel_Rear.jpg (http://dubfoto.com/displayimage.php?pos=-4079)