On March 2, 2009, at 0720 central daylight time, a Bell 206L-3, N401RL, was damaged when the tail rotor drive shaft and coupling severed while the helicopter was sitting on the ramp with the engine running. The helicopter was operated by and registered to Rotorcraft Leasing Company, LLC, Broussard, Louisiana. The commercial pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the ferry flight conducted under 14 Code of Federal Regulations Part 91. According to the operator, the pilot heard a loud bang and vibration shortly after starting the engine. He immediately shut down the engine, and exited the helicopter. Examination of the helicopter revealed that the tail rotor drive shaft and coupling had severed just forward of the gearbox, which resulted in substantial damage to the tail boom. The helicopter had undergone recent maintenance to the tail rotor gearbox input seal which included the removal of the tail rotor drive shaft from the coupling. When the two components were reattached, the mechanic only hand tightened the bolts, figuring additional maintenance was still planned for the gearbox. He then installed the tailrotor drive shaft cover. The mechanic moved onto another project and did not make a logbook entry of the work that he had completed or that the bolts were only hand tightened. Another mechanic later performed additional maintenance to the gearbox, but the bolts were not checked since the maintenance manual did not require the removal of the tail rotor driveshaft cover. A .2-hour maintenance flight check was conducted and the helicopter was returned to service. The accident occurred on first engine start after it had been returned to service.