This one is very, very hard to see because Chris (Governor) uses a white "Happy Birthday" streamer that is barely visible from the ground.
In the zoomed in part of the clip, Stephan (Ro-Maniac) starts on the left (going right) into a 180 degree turn. Chris starts on the right (going left) into a full 360 degree turn. (The third airplane in the middle is mine and is not involved in the kill). Stephan cuts Chris's string at the start of their respective turns. You can't see Chris's streamer while it's still attached all streched out. But as soon as Stephan cuts it, you can kind of see it shimmering as it bunches up in the sky.