As many of responses have mentioned, it is usually a holding pattern during heavy traffic. Different airplanes will perform their holding pattern on different flight levels to allow these patterns to overlap. read more
John Cox , Special for USA TODAY Published 3:00 p.m. ET Dec. 8, 2013 When planes make seemingly random turns in the middle of a flight, it may be because air traffic control is trying to increase the distance between two aircraft. read more