A minor thing, since I don’t want to be too obtuse: my answers above refer to the things actually causing the twinkling. But the “it” as a whole may have contained more of the substances listed above.
Gotta go to bed now. Will check back in ~8 hrs.
Did this event happen during war?
World war II ?
Was the bird a bomber?
Was it the bombing of Hiroshima? Nagasaki?
Was the twinkling object a bridge?
No worries; after all I should perhaps have included “other materials” in my list…! 
Peter Morris, I think military aircraft are already ruled out?
Oh, in that case:
Was it a flight by the Wright brothers?
dr. s
So, we have a man-made structure, at least partly made of metal and glass, which is seen twinkling in the sunlight shortly after dawn by an observer sitting in an aeroplane? Correct?
Is this on a somewhat historic flight?
Is the observed structure, in itself, somehow of historic interest?
Is it on the northern hemisphere?
Is it on a positive longitude (i.e. between 0 and 180 degrees east of Greenwich)?
Is it on a latitude between 0 and 40 degrees (from the equator, north or south)?
Another point of clarity: there seems to be a focus on a singular object here. But consider that “twinkling” can be used in multiple ways: “the night sky twinkled” vs. “the star twinkled”.
Also, since the answers have more or less described the basic setup of the event at this point: I was the observer in the aircraft, on a perfectly ordinary commercial flight, and observed the twinkling on the ground.
Correction:
Was the twinkling caused by normal street lights or automobile lights on the ground?
dr. s
Was the plane flying east?
Was the plane flying into darkness?
Was reflected sunlight from the plane hitting the ground?
Was the darkness the inside of the plane?
dr. s
Perhaps I’ll be repeating others or myself, but to make sure:
Was this incident or moment famous?
Was there a negative effect of the twinkling? A positive one?
Was the twinkling from something man made?
Was the twinkling made by creatures other than humans?
(sorry for the delay… got sidetracked today)
To refresh, since this is a bit of a long one:
The twinkling was from man-made artifact(s) on the ground, made in part from metal and glass. It was observed by (at least) one passenger from an ordinary (non military) airplane. The twinkling itself was reflected sunlight.
Unanswered so far is what “the darkness” represents, other than that it does refer to an absence of light, and is not a name for something.
Is the darkness an eclipse?
dr. s
Was it the shadow of the aircraft?
dr. s