On January 3, 1997, at 1330 eastern standard time, a Bell 206A, N555SJ, sustained substantial damage from a hard landing while performing a practice touchdown autorotation at the Linden Airport (LDJ) near Linden, New Jersey. The airline transport rated pilot and the private pilot rated copilot, the sole occupants, reported no injuries. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The local instructional flight was conducted under 14 CFR Part 91 and originated at the Linden Airport at approximately 1300. The pilot reported, "While practicing full autorotations I attempted to demonstrate a 180 degree autorotation to the ground to the owner of the aircraft, who is himself a private helicopter pilot. While turning to the touchdown spot I noticed the RPM decaying, I attempted to recover the RPM by entering the flare early and prior to completing the turn, however the helicopter mushed through the flare and impacted the ground at a high rate of descent, and caused damage to the rear cross tube. After the immediate impact the helicopter became airborne again and collective application was used to conclude the auto with the helicopter in an upright position." The copilot reported, "While practicing full touchdown autos with my instructor ... he asked to demonstrate a 180 degree auto. With [the instructor] at the controls, he entered the auto and began his turn to the touchdown zone. As we completed the 180 degree turn to touchdown, I noticed that the aircraft's sink rate was unusually high. As he entered the flare, the aircraft did not respond very well to the flare and as he pulled collective to cushion the touchdown, the aircraft impacted the ground very hard. The aircraft came to rest about 100 yards from the touchdown spot after which we secured the aircraft and exited normally."