On May 15, 2006, approximately 2000 mountain daylight time, an experimental Helmer Avid Magnum, N124WT, collided with a fence during a takeoff from a private airstrip near Big Timber, Montana. The private pilot, who was the sole occupant, was not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The pilot was departing in visual meteorological conditions for a local personal flight. According to the pilot, at the beginning of his takeoff roll, the aircraft door popped open, so he shut it. Then a few moments later, the door popped open again, and the pilot closed it a second time. While he was closing the door for the second time, the aircraft veered off the left side of the runway. At that point, the pilot saw that the aircraft was heading for a gate post and a fence, so he pulled the stick back in hopes of clearing the obstacles. But, the aircraft's left wing impacted the post, and the aircraft spun around about 200 degrees, and came to rest with its right wing entangled in the fence structure. After the accident, the pilot stated that his attempt to close the door had distracted him, and that he should have put 100 percent of his attention on the takeoff, and taken care of the door after he was airborne.