On March 16, 2003, at 2015 eastern standard time, a Bell 430 helicopter, N431UM, piloted by an airline transport pilot, was substantially damaged when the tail rotor impacted a roadway sign during an aerial taxi. The accident occurred on Highway M-59, east of US Highway 23, near Highland, Michigan. Visual meteorological conditions prevailed at the time of the accident. The medical evacuation flight was operating under the provisions of 14 CFR Part 135 and was not on a flight plan. The pilot was the sole occupant at the time of the accident. He reported no injuries. The flight departed the University of Michigan Medical Center Heliport (MI32), Ann Arbor, Michigan, at 1959 est, with the intention of returning to MI32 after picking up a patient. According to the pilot's statement, he overflew the area from west to east to review the landing site. He stated that he reversed course and approached the landing site from the east. Prior to touchdown the pilot reported he rotated the aircraft and landed on an easterly heading, at which point the medical crew departed the helicopter. The pilot decided to reposition the aircraft to face west for departure. After notifying local authorities and clearing the helcopter, he reported he began to taxi to the east. He stated he "cleared the tail to move left into the turn around along M-59. I started to move the aircraft which now was facing south into M-59 ... when the tail rotor hit a steel reflector post. The aircraft became airborne to around five or six feet when I lowered the collective and rolled the throttles to idle to stop the aircraft rotation." The aircraft impacted on the left rear skid first and came to rest one-hundred eightly degrees from its initial heading. A post-accident examination revealed the tail rotor and gearbox had departed the helicopter. The pilot reported there were no mechanical malfunctions with the helicopter prior to the accident.