On April 30, 1997, about 1810 eastern daylight time, a MBB (Messerschmitt) BK117-A1, N122LF, was substantially damaged as it impacted the ground during landing at Kane Hospital, Kane, Pennsylvania. The certificated airline transport pilot, a passenger observer in the cockpit, and the two medical personnel in the cabin area, were not injured. The helicopter, owned by the Geisinger Medical Center of Danville, Pennsylvania, was operated by Keystone Helicopter Corporation of West Chester, Pennsylvania. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed for the positioning flight conducted under 14 CFR Part 91. The flight originated from the Bellefont Airport (N96), Bellefont, Pennsylvania, about 1727. The pilot reported that the helicopter performed a normal takeoff and a uneventful 30 minute flight en route to Kane, Pennsylvania. He stated that upon his arrival, he circled the town looking for the hospital. On the second pass, the pilot identified the hospital. He described the helipad as small, located in a clear area which was about 60 to 75 yards square. Wires, about 40 feet high, were on the north side of the clearing, and trees, varying from 35 feet to 50 feet in height, surrounded the rest of the area. The pilot reported that the windsock indicated about 3 to 5 knots from the west/southwest. He stated that his approach path to the helipad was based on the lowest obstacles surrounding the helipad, which was from the southwest. The pilot decided to descend vertically to the helipad. He slowed his airspeed below 10 knots and attempted to stop his descent rate at 50 feet agl. He stated that the helicopter shuttered with the application of additional power at about effective translational lift (ETL). The helicopter yawed right, and the pilot stated that "the additional collective pitch seemed to have no effect on slowing the rate of descent, the rate of descent seemed to increase at this point." The pilot stated that a "fly away" was not possible due to the proximity of the trees and wires, so he announced to the crew, "We're settling in guys!" The pilot reported that he did not recall any master caution or annunciator panel lights illuminating nor any audio tones because he was focused outside the cockpit. He stated that he continued to pull collective pitch, and at the time of touchdown, all remaining collective pitch was applied. With about 2 to 3 knots of forward airspeed, the helicopter impacted the ground and rotated to the right. The pilot recalled reducing the collective immediately to arrest the yaw rate. The helicopter stopped after completing a 180 degree turn. A Federal Aviation Administration (FAA) Inspector conducted a preliminary examination of the wreckage. The main rotor blades were damaged, the landing skids were bowed out, the helicopter was resting on the rear fuselage, and the tailboom was separated and lying on the ground next to the right side of the helicopter. The Inspector reported that he was able to verify control continuity of the cyclic and the collective and "found no reason that the anti-torque system should not have worked." The wreckage was transported to Keystone Helicopter Corporation in West Chester, Pennsylvania. Representatives from the helicopter and engine manufacturers, the operator, the Federal Aviation Administration, and the Investigator in Charge from the National Transportation Safety Board met to examine the wreckage on May 13, 1997. Rigging for flight controls and power train were verified and no anomalies noted. Fuel samples were taken from five drain areas, with the aft right sample rust orange in color, and the others yellow. The samples were sent to the AlliedSignal Chemistry Lab for testing. The aft right sample was found to contain red dyed (high sulfur) diesel fuel. The differences noted were in viscosity, color, and freezing point. Only the freezing point did not meet Jet A specifications of -40 degrees Fahrenheit. The sample was determined to have a -31 degrees Fahrenheit freezing point. Both engines were removed and placed in a test cell on May 14, 1997. It was noted after the removal of the left engine that a bolt was missing from the plenum. A test run was completed with the bolt out, and then with the bolt replaced. The engines were determined capable of producing their assigned horsepower. The fuel filters were removed from both engines after the testing. Both filters had accumulated debris which consisted of dirt, fibers, a black 'rubber-like' compound and a trace of metallics. A U.S. Army manual, FM 1-203 Fundamentals of Flight, stated under the topic, Settling With Power: "Settling with power is a condition of powered flight in which the helicopter settles in its own downwash...Conditions conducive to settling with power are a vertical or near vertical descent of at least 300 feet per minute and low forward speed. The rotor system must also be using some of the available engine power (from 20 to 100 percent) with insufficient power available to retard the sink rate. These conditions can occur during downwind approaches...[and] steep approaches..."