[NittanyLion]

The ‘visible horizon’ is much further away if the observer and the object are both at 35,000ft, of course. If my calculation is correct, I get about 700 miles for the distance the two could see each other if the air were clear enough.

IIRC, they were ~1400 miles apart. Something like 7 degrees of latitude and 19 degrees of longitude. I'm trying to find the translated article that includes the Air Comet position, but I can't seem to locate it.

[expatpat]

If they were 1400 miles apart (more than DC to Chicago), it seems silly talking about the Comet flight seeing anything related to the Airbus. I thought the two were about 30 mins. apart, which would put it at around 250 miles if they were traveling in more or less the same direction (and 1000 miles if in opposite directions), but the 30 mins. may not be right.