It\'s a reflection. It appears the first time at 1:10, just under the aircraft that is beeing airborn, moving slowly to the right. The second time it appears at 1:39, just under the tail of the plane in the forground. This time also moving to the right and just as the one before it is visible in front of the planes, crew and deck. (Making it a very, very small \"ufo\")
The third time it appears is at 1:49 and is the one everybody is seeing.
Every time the reflection appears is when the planes taking off is at exactly the same angle. The reflection is moving in proportion to the aircrafts. The reason the reflection appears in different locations on the screen is that it has gone some time between the takes (yes there is cuts between the three instances) and we all know that the sun moves in the sky. Occams razor says to me that this is more likely to be reflection.