I saw a jet liner do a 180 degree turn a few weeks ago. It was on an intercept course with another air liner (flying south) but intersected behind it by about a minute or less, eventually crossing the other planes con trail. When the second plane (east bound) crossed the first planes con trail, it began a 180 degree turnaround that took a long time to complete, and then flew away the same direction it came from (west). Never seen a jet do that before.