Midair collisions can be a problem with almost all air sports, and whether you're in a machine or free falling, crashing into something can seriously hamper your fun. Collisions are among the leading causes of skydiving-related fatalities, accounting for approximately 15 percent of deaths [source: Dropzone]. Midair collisions can also happen in planes. In 2007, a pilot at the Reno Air Race was killed when his plane barely clipped a pylon set out to mark the course [source: Lyons].
Additionally, there is a long history of pilots running into power lines and tall trees -- especially during crash landings. The natural instinct for a pilot in an emergency is to land on a. Since power lines often parallel country roads, it's easy to hit or get tangled up in them.
Most aircraft have a detection system that can help pilots avoid midair collisions with larger craft, but sports like skydiving or paragliding don't have these warning systems. Instead, you need to keep your head up and be aware of your surroundings -- even if you think you're alone in the air.