On June 13, 2003, about 2020 mountain standard time, an experimental Kowtun Mini 500 helicopter, N919WK, experienced a loss of directional control, collided with the ground, and rolled over at Phoenix Deer Valley Airport (DVT), Phoenix, Arizona. The pilot/owner was operating the helicopter under the provisions of 14 CFR Part 91. The pilot, the sole occupant, was not injured. The helicopter was destroyed. Night visual meteorological conditions prevailed, and no flight plan had been filed. The primary wreckage was at 33 degrees 41.17 minutes north latitude and 112 degrees 4.17 minutes west longitude. In a written statement, the pilot reported that he had just "tweaked" the carburetor and was performing a hover taxi test flight when the helicopter "started to spin to the right and would not respond to the left pedal." It then impacted the ground, rolled on its right side, and was consumed by fire. In the section of NTSB Form 6120.1/2, which asks if there was a mechanical malfunction or failure, the pilot wrote "tail rotor drive shaft failure." A Safety Board investigator contacted the pilot on July 21, 2003, to learn more about the tail rotor drive shaft issue. The pilot, however, stated that the Federal Aviation Administration was trying to revoke his license and would not answer any questions pertaining to the accident. He then referred the investigator to his lawyer. Subsequent attempts to gain further information from the pilot or his attorney were unsuccessful.