Members and visitors to the website http://cloudappreciationsociety.org/ will have enjoyed the many examples of ‘fallstreak hole’ clouds that we have on our gallery. These look like a layer of cloud in which a hole has been punched out, with plumes of ice crystals falling below. While there has, for some time, been debate about the cause of these formations, there is now clear evidence that at least one cause is aircraft causing the cloud's droplets to freeze as it flies through the layer. It is quite common to see fallstreak holes in long lines, known as distrails, where the aircraft has banked gradually through the layer.
For more information about the effect of aircraft on fallstreak holes, see here
http://www.sciencedaily.com/releases/2010/06/100614141344.htm