This can lead to a violent crash as the rider, with or without the tube, falls back to the surface of the water. To address the poor flight characteristics of most tubes and to target thrill seekers, tubes specially designed for kite tubing have been introduced. These tubes may feature channels to allow air to flow through the tube's body, a transparent "window" for the rider to signal the boat operator, as well as more streamlined, aerodynamic designs. As of July 2006, 39 injuries and two deaths from kite tubing have been reported. Injuries have included a broken neck, punctured lung, cracked ribs, a concussion and injuries to the chest, back and face. Some accidents have been linked to gusts of wind that unexpectedly altered the flight characteristics and ejected the riders. In cooperation with the U.S. Consumer Product Safety Commission (CPSC), Sportsstuff Inc. voluntarily withdrew the Wego Kite Tube from the market on , 2006. Related to kite tubing is the kited inflated wing, a stiffened, flexible wing or gas-inflated bladder wing, where a control bar is affixed for the kited person to direct the inflated wing so the dangerous lock-out does not occur. The kited person can have a quick disconnect to release from a towing boat or car if a dangerous angle of tow begins. Summer tubing is the summer variant of snow tubing. Hard bottom tubes slide down artificial slopes, usually made of special plastic. They can be installed on mountains by ski resorts or you can find them also in amusement parks. In Europe produced by Neveplast, Tubingsystem and Mr. Snow.  Tubing can require varying pieces and kinds of equipment depending on the variety of tubing one wishes to engage in. The one common piece of equipment across all forms of tubing is the tube itself. While tubes vary in construction, all share the general characteristics of being:  Tubes for use as towables on water are generally not true inner tubes but rather specially designed tubes for the purpose of recreation. These tubes are often fairly durable and come in either donut or disk shapes. A sleeve of synthetic fabric often covers the tube to prevent it from becoming elongated during towing. Such sleeves commonly have handles for the rider to grasp and an anchoring point for the tow line to be attached at. Towing a tube or tubes also requires a powered watercraft such a motorboat or personal watercraft as well as rope to tether the tubes to such craft. Tubes used for free-floating tubing have traditionally been true inner tubes, but commercially sold tubes for the same purpose are becoming common place.