Could be, it was at cruising height though and lasted for most if the flight, which I guess is around 27-35k ft. It was over France, so it might have been Frenc

Could be, it was at cruising height though and lasted for most if the flight, which I guess is around 27-35k ft. It was over France, so it might have been French onion smog! I kind of remember seeing it when I flew to Iceland recently too, (North Atlantic) which I know is a popular route for big carriers. Definitely no cities there.