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glass cockpit safety question (Are the LCD screens armored)

Posted: Fri Jan 31, 2020 4:46 pm
by boacvc10
I enjoyed the perspective shown in
of an A350-941 cockpit instrumentation. Putting on my designer hat on, I was wondering, what if something hit those screens, or some object / body with capacitance brushed the screen. Obviously I am talking / considering during abnormal situations not during regular ops. Are the screens display only, or interactive?

How tough are the flat panel screens, and are they touch sensitive? I'm curious how testing was performed to check out if debris during an upset (some object flying forward or accidental contact) affects the screens, and if they are touch, how inputs are blocked that are accidental. If you look at the vast majority of aerospace and spacecraft controls, mechanical protectors such as http://www.periheliondesign.com/switchguards.htm or similar are used.

A corollary would be the question of redundancy, in case one of the screens goes kaput. A few months ago I accidentally dropped a Mac Book Pro, and it fell on a corner of the table just where the apple logo is cut out of the back of the aluminum shell --- and hence the LCD screen was severely damaged, albeit from the back, not the front in my case. It worked but we could not see anything for several months until I spent $$$ to get it repaired. BTW LCD screens are fragile, even with a screen protector.

But given the curvature of the cockpit, is a curved display (segmented?) in the works? See https://www.corning.com/gorillaglass/worldwide/en/applications/automotive/automotive-interiors/bending-the-rules.html

Separately, is a different standard applied for LCD display control (if touch) - and not FCC guidelines such as https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_20-175.pdf

regards

BOACVC10

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Fri Jan 31, 2020 6:06 pm
by GalaxyFlyer
There’s a variety of reversion modes to display data on other screens to bypass a inop one. I don’t think they’re armored at all,

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Fri Jan 31, 2020 7:07 pm
by bhill
They may stop a bullet...coffee?.....not so much.

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Fri Jan 31, 2020 7:15 pm
by Flow2706
Ok the A350 there is an option to have touchscreens, but on most, if not all, civil aircraft except for the 350 they are displays only. I have never seen a screen physically breaking, they are pretty robust (occasionally the power supply or the computer generating the image fails or the image gets distorted, but the screen itself is alright). The closest I have seen was in a Level D Simulator (A320) where the screen had a small crack but was still fully functional (I guess on the aircraft it would have been replaced, but it was still okay for the sim). The instructor told me that some new student managed to leave a pen on the table and then forcefully closed it thereby cracking the screen that is directly over the table (quite hard to believe as it would take a lot of force to archive that...but I guess it must be possible somehow). But as I mentioned the screen was still useable afterwards it was only „cosmetic“ damage.
Regarding the touch screens on (some of the) 350s, I heard the functions that can be activated by touch are not flight critical functions but rather functions to customise the display etc, so inadvertent action on the touchscreen wouldn’t have severe consequences...

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sat Feb 01, 2020 2:13 am
by Starlionblue
As Flow2706 says, the flight critical functions on the A350 are never touch-enabled. The touchscreen option is only for the outer display units, used for charts, performance calculations, manuals, ACARS, and such ancillary functions. The inner display units, used for PFD and ND, and the center display units, used for MFD ("FMS") and systems status, are just displays.

Screens do break sometimes. That pen thing happens. A forgotten pen is stuck in the tray table once it has been folded. The pilot now tries to stow the table. You're supposed to be gentle, but even so, a pointy object would probably not have to work very hard to punch a hole in a screen. Oops. This is one of the reasons we are told never to leave our pens on the table, the other reason being the pen rolling off the edge onto the floor. Your pen should always either be in your hand or in your pocket.

All that being said, an inop screen is much more likely to be caused by something other than the screen itself. It will be either a display controller or the circuitry running the screen.


boacvc10 wrote:
How tough are the flat panel screens, and are they touch sensitive? I'm curious how testing was performed to check out if debris during an upset (some object flying forward or accidental contact) affects the screens, and if they are touch, how inputs are blocked that are accidental. If you look at the vast majority of aerospace and spacecraft controls, mechanical protectors such as http://www.periheliondesign.com/switchguards.htm or similar are used.

A corollary would be the question of redundancy, in case one of the screens goes kaput. A few months ago I accidentally dropped a Mac Book Pro, and it fell on a corner of the table just where the apple logo is cut out of the back of the aluminum shell --- and hence the LCD screen was severely damaged, albeit from the back, not the front in my case. It worked but we could not see anything for several months until I spent $$$ to get it repaired. BTW LCD screens are fragile, even with a screen protector.

regards

BOACVC10


We try very hard not to touch the screens, but you will see the occasional fingerprint. They're also in positions where it isn't really natural to hold stuff over them or near them.

Mechanical protectors like that are not used a lot, but there are other types of guards. It is quite difficult to push any button by mistake as there is rather a lot of resistance. If you see someone programming an FMS, you might notice every button press is quite distinct. Guards on pushbutton do exist, but only for stuff you don't want to activate by mistake, e.g. flight control computer on/off. On Airbus, black pushbutton guards, except for stuff that is irreversible, e.g. pax oxygen masks or RAT, which have red guards. This design logic is also valid for twist controls like ADIRS. You need to pull the knob out, then twist, as opposed to the crossbleed control which you can just twist.

Kaput screens are easily dealt with. Just use another screen. It even works the other way. If the ACP (autopilot control panel on the glareshield) breaks on the A350, you can run the functions from the MFD on the lower central display unit.

The MEL even allows dispatch with an inop inner display unit. It's a bit weird flying with all your instruments off to one side and canted, but not really a problem.


bhill wrote:
They may stop a bullet...coffee?.....not so much.


:rotfl: :rotfl: :rotfl:

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sat Feb 01, 2020 5:35 am
by spacecadet
One thing I will add is that those display units (and that includes more than the screen, but I'm not sure you can replace only the screen itself) cost in the tens of thousands of dollars. As you can imagine, pilots are generally pretty careful around them! Or at least the airlines would prefer them to be, and let them know it.

As for redundancy, it's pretty standard across cockpits to have both a PFD and MFD for both pilots, which are the exact same thing, just sometimes showing info from different sources (depending on SOP and pilot preference). A little disclaimer in that some of what I'm about to say may not apply to every plane, just the ones I know, but most of it surely does. If a pilot's MFD goes dark, he/she will typically just look at the one on the working side; it's not a huge deal. If a pilot's PFD goes dark, he/she will revert the working MFD to be a PFD, since you can't easily fly without a PFD. Even as pilot monitoring, it's more important to have a working PFD, and you just look over to the working MFD on the other side.

Then there's an EICAS in the middle, which is the odd man out in that there's usually only one of them by default. If the EICAS goes dark, typically the pilot monitoring would switch his MFD to be the EICAS, and then he would look at the other pilot's MFD as if his own MFD was dark.

So basically in all cases, whatever screen breaks, you would just lose one of the two MFD's. The display units are multiple redundant. The PFD and EICAS take primacy, though; the MFD is always what you lose. Worst case, you need to look over a couple feet extra to see what you need to see. Not all airplanes may work like this, but the ones I know do.

Lastly, this is something pilots are specifically trained on. I just did my initial jet training and it was the first non-normal procedure I was given (because it's easy; cockpit failures don't really get any more benign). It was also one of the first things I learned even as a PPL training on a G1000. So you're trained on reversionary modes and practice them at every level. I don't honestly know how common display unit failures are at the airlines, but I have had DU failures in the G1000 multiple times. (Along with pretty much every other kind of electronics failure you could think of.) Problems like that do tend to be a lot more common in the GA world than at the airlines, but that also means most pilots have probably gotten used to them long before arriving at the airlines. A DU failure just isn't a big deal to a pilot.

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sat Feb 01, 2020 9:01 am
by Starlionblue
You're not likely to have to switch your ND to ECAM. Even an Airbus A320 or A330 has six main screens, of which two are for systems display.

The A350 PFD and ND are on the same screen. But you still have six screens as you have "gained" the outer display units. Then again you have "lost" the dedicated MCDU screens, as those functions are now on the lower center display unit.

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sun Feb 02, 2020 5:49 pm
by boacvc10
Thank you posters. Learned a lot.

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sun Feb 02, 2020 9:40 pm
by Agent
Starlionblue wrote:
As Flow2706 says, the flight critical functions on the A350 are never touch-enabled. The touchscreen option is only for the outer display units, used for charts, performance calculations, manuals, ACARS, and such ancillary functions. The inner display units, used for PFD and ND, and the center display units, used for MFD ("FMS") and systems status, are just displays.


Little correction here: MFD Screen is touch sensitive as well, when used as OIS/EFB Screen. In MFD Mode it is not.

Re: glass cockpit safety question (Are the LCD screens armored)

Posted: Sun Feb 02, 2020 11:24 pm
by Starlionblue
Agent wrote:
Starlionblue wrote:
As Flow2706 says, the flight critical functions on the A350 are never touch-enabled. The touchscreen option is only for the outer display units, used for charts, performance calculations, manuals, ACARS, and such ancillary functions. The inner display units, used for PFD and ND, and the center display units, used for MFD ("FMS") and systems status, are just displays.


Little correction here: MFD Screen is touch sensitive as well, when used as OIS/EFB Screen. In MFD Mode it is not.


Ah got it. Well that makes sense since you can display charts there for briefings and so on. Flip the dusplay from the outer display units.