On July 14, 2005, about 0810 central daylight time, a Messerschmitt BK 117 B-2 twin-turbo-shaft powered helicopter, N440HH, was substantially damaged following an airframe component failure while on approach to the Pearland Regional Airport (LVJ) near Houston, Texas. The commercial pilot and two crewmembers were not injured. The helicopter was registered to and operated by Memorial Hermann Hospital Systems Incorporated. Visual meteorological conditions prevailed and a company flight plan was filed for the 14 Code of Federal Regulations Part 91 positioning flight. The local flight originated from the company's refueling farm near Fresno, Texas. According to the 7,135 hour pilot, while on an extended downwind for runway 14L the crew requested to open the left sliding passenger door. The pilot approved the request and at an altitude of approximately 100 feet above ground level (agl), and while at 55 knots indicated airspeed, the left sliding passenger door exited the helicopter and made contact with all four main rotor blades. The pilot immediately descended to a three-foot agl hover and with no indication of control problems, proceeded approximately 1,800 feet to a helipad and landed. An inspection of the helicopter by a Federal Aviation Administration inspector revealed that the leading edge of all four main rotor blades sustained structural damage that would necessitate their replacement. An examination of the sliding door and attaching hardware revealed that the lower door guide rail had worn sufficiently enough to allow the door to exit the helicopter when the door handle was placed in the open position.