Can someone please tell me what is the purpose of the single small white +'s painted on some of the sub-panels ? Geoff

Can someone please tell me what is the purpose of the single small white +'s painted on some of the sub-panels ? Geoff

They are there for service engineers ! Fred.

They are there for service engineers ! Fred.

Thanks Fred -- I'll add that to my list of Service Requests for the Engineering Maintenance Here are some "actual maintenance complaints" submitted by US Air Force pilots and the replies from the maintenance crews.(P) = problem;(S) = solution. (P) Left inside main tire almost needs replacement.(S) Almost replaced left inside main tire. (P) Test flight OK, except autoland very rough.(S) Autoland not installed on this aircraft. (P) #2 propeller seeping prop fluid.(S) #2 propeller seepage normal - #1, #3 and #4 propellers lack normal seepage. (P) Something loose in cockpit.(S) Something tightened in cockpit. (P) Evidence of leak on right main landing gear.(S) Evidence removed. (P) DME volume unbelievably loud.(S) Volume set to more believable level (P) Dead bugs on windshield.(S) Live bugs on order. (P) Autopilot in altitude hold mode produces a 200 fpm descent.(S) Cannot reproduce problem on the ground. (P) IFF inoperative.(S) IFF always inoperative in OFF mode. (P) Friction locks cause throttle levers to stick.(S) That's what they are there for. (P) Number three engine missing.(S) Engine found on right wing after brief search. (P) Aircraft handles funny.(S) Aircraft warned to straighten up, "fly right" and be serious. (P) Target radar hums.(S) Reprogrammed Target Radar with the words. Geoff

I believe the + sign is where any backlighting bulbs in the panel are located.

I believe the + sign is where any backlighting bulbs in the panel are located.

Thanks -- OK, that seems a more possible answer. Perhaps you could expand on that, as some panels that would appear to also have backlighting, do not have these +'s

Are you talking about the X's in the top right corner? Or am is there something else I'm not seeing.

When I flew for Mesa another pilot told me that it was a tap spot to hit if a panel wasn't lighting up. I asked some mechanics and they provided the most plausible explanation I've heard so far. They told me the + signs are stencil alignment marks for when the panels become worn and need repainting. Who knows. I flew jets and turbo props from three manufacturers for 10 years and and looked at little + signs everywhere and never could find out the absoloute truth of their purpose!!! Hiram Hunt

I believe the + sign is where any backlighting bulbs in the panel are located.

After further research, this is clearly the correct answer. The white cross shows the location of the "LIGHT PLATE" backlight bulb.Not all panels have :"LIGHT PLATES" The idea of TAPPING on the +, would tend to come from finding that sometimes the bulbs make intermittant connection, or are partly defective, and TAPPING close to them (ie on the white plus) can sometimes coax them back into life. Personally, I find that VERY SCARY !! Intermittant electrical connections . Some answers talked about "this is where the Connector is located" .. well, it would seem that the "Connector" in question is really the Lamp Bulb socket. So that makes sense as well, in a more obscure way. The ENGINE panel with the light-plate fitted. The ENGINE panel with the light-plate removed What is also interesting is that, while the Illuminated Push Buttons have Pairs of bulbs (for redundancy), the "Light Panels" only have ONE Bulb. Geoff

Speaking of maintenance, I worked on A-6E's and F/A-18's for a number of years...oh the stories that could be told, lol...particularly with the A-6's (old birds=many quirks). We did use the good ole, "Tests good in the 'O-N' position" more than a few times. ;)

The older 747's had these small white crosses painted on the panels and they showed the position of the panel lighting 'earthing' points. Thats why you tapped them if the background lights stopped working. Very often it worked so they were very useful ! Glen

Actually the panels don't have any bulbs at all. The panels themselves are electo-luminescent and the entire panel glows. The letters light up because the panel is painted, and then the markings are engraved through the paint to expose the glowing panel underneath. The little crosses are to mark where the contact point is that powers the panel. As was previously pointed out if the panel stops working sometimes you can press on the contact point to reset the power pin into the receptacle kind of like pushing a power plug back in that has backed out of the outlet.

The older 747's had these small white crosses painted on the panels and they showed the position of the panel lighting 'earthing' points. Thats why you tapped them if the background lights stopped working. Very often it worked so they were very useful ! Glen

What exactly do you mean by "EARTHING POINT" ?? I assume this must be reffering to the light bulb "SOCKET", and its use of the GROUND/EARTH to provide the return electrical apth for the bulb ? Once again, it seems like the Bulb making a bad connection to "EARTH/GROUND" could psoosibly be temporarily corrected by Tapping/Banging in that area. In any case, -- where there is a "little white cross", there would seem to be a corresponding "Light Panel" backlight bulb. The last part of the Question now is... (q) Are those old Incandescent bulbs in 737s , now replaced by more efficeint, cooler running, longer lasting LED Bulbs ? Geoff

Actually the panels don't have any bulbs at all. The panels themselves are electo-luminescent and the entire panel glows. The letters light up because the panel is painted, and then the markings are engraved through the paint to expose the glowing panel underneath.The little crosses are to mark where the contact point is that powers the panel. As was previously pointed out if the panel stops working sometimes you can press on the contact point to reset the power pin into the receptacle kind of like pushing a power plug back in that has backed out of the outlet.

AHHH .. makes perfect sense now .... Thanks .. So thats what they mean by a "LIGHT PANEL" Geoff

Yes, that is why they are sometimes referred to as light panels. They are kind of like those flat night lights that you buy at the grocery store, only thicker and more robust. There is a simple pin that sticks out the back and when you screw the panel on the pin is pushed into a sort of metallic tube and makes contact. The circuit is completed by a ground path through one of the mounting screws.

What exactly do you mean by "EARTHING POINT" ??

I was a maintenance engineer on the 747-100,200 series aircraft although not an electrician. As the panels either slide out or fold down they require a common earthing point I believe in the form of a quick fit type connector. As you may know lighting circuits on aircraft usually did not have earth return cables to save weight. During use, vibration and a white 'powder type' deposit used to accumulate behind these panels, thus causing occasional poor connections. The white cross marked the position of these connections, usually, pushing fairly hard on the white cross rectified a fauly light problem - at least thats how it worked on older Boeing's, can't speak for the new generation aircraft Glen