Abstract: Employee #1, a logger, was holding onto a tree shoe to guide the tree jack to the ground as the yarder operator slackened the skyline. The tree jack, used in the intermediate support tree, was sent to the landing on the slack pulling carriage. The yarder operator slacked the skyline and Employee #1 held onto the tree shoe to guide it to the ground. To slack the skidding line through the carriage, the skyline clamp must first be activated and then the skidding line clamp can be released. These two functions are controlled by one toggle switch. The skidding line clamp was inadvertently activated first, releasing the skidding line and causing the carriage to suddenly run down the skyline until it slammed into the stop plate at the end of the dropline. Employee #1 was unable to let go of the tree jack in time and he was thrown approximately 10 ft off the landing. He sustained cracked ribs and a head laceration, for which he was hospitalized.