On February 1, 2003, at 0945 eastern standard time, a Robinson R22 helicopter, N528EE, registered to a private owner, leased to Heliflight Inc., operating as a 14 CFR Part 91 instructional flight, collided with an unknown object on the ground during a run on landing at Fort Lauderdale Executive Airport, Fort Lauderdale, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The helicopter rolled over on its left side and sustained substantial structural damage to the cabin and tailboom assembly. The private pilot and airline transport rated check pilot reported no injuries. The flight originated from Fort Lauderdale Executive Airport, Fort Lauderdale, Florida, at 0830. The private pilot stated he was demonstrating a run on landing to the check pilot. The helicopter touched down in the sod area adjacent to runway 08 in a level attitude at or above effective translational lift. During the deceleration the left front skid contacted "something" which slowed the helicopter rapidly. The pilot stated he lunged forward in his seat and inadvertently moved the cyclic forward and to the left and increased collective pitch. The helicopter pivoted around the toe of the left skid and rolled over on its left side before he or the check pilot could take any corrective action. He further stated the helicopter did not experience any mechanical failure or malfunction. Examination of the crash site did not identify the unknown object that the helicopter collided with.