Lets assume the panel was found as shown in the photos...

As DaveReidUK says no visible damage to the countersink holes.
Also no visible bolts or parts of them.
Which might suggest the panel had been temporarily fastened by maintenance with one or a few bolts or temporary fasteners.

Take the lady up. Vibration and force shears off the first. Then the second. Releasing the panel. Little visible damage.

Nothing to see ? I disagree with that. Shedding parts is always a serious issue. Both for plane strikes and striking anything else.
Have not heard about the bracket failing. What damage would you have seen on the panel if it did? You would expect at least part of that attached... With some bolts left... Or not?

Might be interesting to see the relevant shots of the aircraft on arrival.

The panel is made of nonmetal compound materials and is part of the base of the right wing.
Explains why it isnt bent....

https://i.imgur.com/6EtREAK.jpg

Lets assume this aircraft was assembled first, then painted. Also assume that if it was a lapped piece, (underneath another) the paint would reflect this.

I do no notice any paint circle of base primer that would indicate fasteners missing. I would think that if it was fastened, then painted, removing the fasteners would leave a ring of base primer. Looking at the image, it appears that some of the holes are painted.

https://i.imgur.com/x64FJtW.jpg


If a piece was lapped, again underneath would prevent paint of the lapped section, and would be evident.
What I note in this portion of the panel, is full paint, and no fastener holes at all.

https://i.imgur.com/saMErnS.jpg

I think that's a safe assumption. :O

But on the other hand, if the panel has been replaced at some time during the aircraft's 14 years in service, it's likely that it would have been painted before fitting, which would explain the paint in the countersinks.

:Dtrue..

a flexible piece that comes off inflight, with little/no visible damage or paint missing from the fastener holes....it could happen.

a 777 on the way to paint, showing the panel..

https://i.imgur.com/o5EQFFX.jpg

261 and Safety
 

Though not directly applicable to this specific, particular occurrence, nonetheless the facts - as they have emerged so far - do tend to suggest validity and importance to the question whether EU 261 and airline penalties for delays can compromise, and may in fact already be compromising, safety. That is, to the extent maintenance issues are not typically or textually considered to qualify as extraordinary circumstances such as to cancel the penalty obligation, this state of regulatory affairs tends to motivate, or create an incentive for, less rigor in maintenance practice. Not wanting to cause a delay on a flight, someone forgets (forgive the paltry pun) to turn the screws. Or the fasteners.

I think you are correct in that the pressures of EU 261, if any, aren't relevant to this incident.

The investigation will no doubt be able to determine when that panel was last disturbed, and it's very unlikely to have been on a turnround.

It may or may not be relevant that the aircraft in question had a couple of 3-day spells on the ground at AMS at the end and beginning of August, possibly on some sort of maintenance input.

That panel doesn't look like it's been on the aircraft for all that long.

If you look at this top row of holes and number them from left to right 1 through 7, then the first two holes (1 and 2) look a bigger than the others.

http://www.sbowden.org/misc/PANEL-777-KLM-2.png

The bush is behind hole #1, and you can see quite a bit of it. My guess would be that the there was a screw in hole #1 temporarily holding the panel in place - and that screw is still with the aircraft.
Hole #2 also looks a bit larger than the next 5, so maybe there was a screw there as well.

Or, perhaps holes 1 and 2 took bigger screws. But even at that, hole #1 looks pretty big.

I don't know. If I was told that I just lost 5 square feet of my fuselage paneling, I would worry about what else was left undone.

Lets say I am (very) close to the fire. No need to say more. Just want to clear KLM mx.

On the contrary. If your aim is to eliminate one of the (several) possible scenarios, you're going to have to come up with a lot more than that.

Aerospace safety investigations on accidents and in this case an incident ... are about finding out what happened, then why it happened, followed by devising and implementing ways to prevent it from occurring again. They are neither about clearing nor blaming anyone.

At this stage it still is about ...'What'... Which means, like @DaveReidUK posted, listing possible scenarios. Hope for better and more detailed pictures as well as more information.

@ErwinS... Would be interesting if you could provide public domain links to similar cases (you suggested there are some) or Boeing bulletins.

Depends which part of the world you live/work. :(

Be good to see a photo of the panel surround on this particular aircraft as it arrived.
Also the back of the panel.

This particular panel coming adrift has been an issue for years, the support bracket design isnt the best in the world. If you have access to myboeingfleet there is a long discussion about it.

A I said;-) Thiswas indeed a bracket failure. But people like to speculate ....

Bracket Broken
 

If we are to accept the info from Erwin S quoted above we should also ask "where is the bracket and, if a bracket failed, where are the numerous attachment screws which held the panel in place?" Having removed and replaced many panels during my aviation career I have no doubt this is the result of a maintenance error.

Think what you want. Just saying it is not a mx error.

And no I won't post any official Boeing docs.

Sure, blame it on the old "bracket failure" thing :*

Okay, fair enough

Out of interest, which side(s) of the panel are attached to the bracket in question ?

And what are the other sides of the panel attached to ?

If the bracket failed, why isn't the failed part of the bracket still attached to the panel ?

In fact, how come every single screw has disappeared ?