On April 27, 2004, at 0831 central daylight time, a Robinson R22 Beta helicopter, N40725, piloted by a student pilot, was substantially damaged during an in-flight collision with terrain during landing on runway 31 (7,533 feet by 150 feet, concrete ) at the Rochester International Airport (RST), Rochester, Minnesota. The solo instructional flight was being conducted under 14 CFR Part 91 and was not on a flight plan. Visual meteorological conditions prevailed. The student pilot reported no injuries. The local flight departed RST about 0810. The pilot reported that he contacted the RST control tower about six miles east of the airport and was instructed to make a straight-in approach to runway 31. About two miles from the airport the pilot noted that he slowed the helicopter to about 50 knots to allow a business jet to depart prior to his landing. He noted that the jet was airborne and was climbing by the time he was 1-1/2 miles from the runway. He noted that as a precaution against encountering any wake turbulence he adjusted his approach path so as to land on the runway numbers. The pilot recalled that the approach was smooth until he crossed the runway threshold about 10 feet above ground level, at which point he "felt very slight buffeting." He stated: "I immediately recognized it as turbulence and decided to abort the landing. I eased the cyclic forward to begin to build airspeed. Within two seconds the helicopter began to pitch and roll severely. It also yawed to the right. I tried to stabilize the helicopter by stepping on the left pedal and by using very deliberate cyclic input (without over-controlling)." The pilot stated that he was not able to stabilize the helicopter. He decided to land in spite of the unstable condition "because [the helicopter] was still upright and [he] wasn't sure if [he] could keep it that way." He reported that he lowered the collective and, just prior to contact with the ground, "pulled maximum collective" in an attempt to cushion the impact. The left skid contacted the ground and collapsed. The helicopter came to rest on its left side. A post-accident inspection conducted by a Federal Aviation Administration (FAA) inspector revealed no indication of any pre-impact anomalies. Collective and cyclic flight control continuity was verified. Anti-torque pedal control continuity was intact except at one location which coincided with a failure of the tail rotor drive shaft. Damage to the tail rotor drive shaft and tail rotor control tube was consistent with damage due to impact forces. The pilot reported that there were no failures or malfunctions with the helicopter prior to the accident. Weather recorded by the RST Automated Surface Observing System at 0754 was clear, with winds from 260 degrees at 5 knots. At 0854, skies remained clear and winds were from 240 degrees at 6 knots. The pilot reported 28.3 hours total flight time and 3.0 hours of pilot-in-command (solo) flight time. FAA Advisory Circular 90-23F, Aircraft Wake Turbulence, states that wake turbulence (vortices) are generated once the aircraft lifts off because wake turbulence (trailing vortices) are a by-product of wing lift. The advisory circular notes that when landing behind a departing larger aircraft on the same runway, the landing aircraft should plan to touchdown prior to the departing aircraft's rotation point in order to avoid the wake turbulence.