i saw the fireball from the air. i was flying west from frankfurt airport to bristol airport in uk. this made it hard for me to answer some of your questions about elevation etc. i was on the left side of the plane when i saw it, so i was looking in a southerly direction. we had been in the air around 15 mins so were already quite high up. it seemed quite close but i guess half way between us and the horizon. it seemed to disappear before it got to the ground (it was quite a clear day with only small clouds). It was really amazing!
