On May 20, 1999, about 1930 Eastern Daylight Time, a homebuilt Twinstar Gyroplane, N6364H, was substantially damaged while attempting a takeoff from Bloomsburg Municipal Airport (N13), Bloomsburg, Pennsylvania. The certificated private pilot was seriously injured, and the passenger received minor injuries. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed for the local flight, which was conducted under 14 CFR Part 91. According to a Federal Aviation Administration (FAA) Inspector, the gyroplane was taking off from Runway 08. The pilot stated that the rotor "began to flop," and that rotor rpm decreased to below the rpm necessary for flight. The pilot said he attempted to increase the rotor rpm by applying aft cyclic, but the cyclic began to move without the pilot's input due to rotor system feedback. The rotor struck the ground below the aft left side of the rotor disk plane several times. The fuselage then made an uncommanded 120-degree left roll, and came to a stop on the left side of the runway. In a later statement, the pilot wrote that during the takeoff roll, his finger slipped off the pre-rotate button at 80 rpm. He continued down the runway to increase the rpm, and about 90 rpm, encountered a severe stick shake, or "violent rotor flapping." It was at that point that he believed that part of the airframe broke, and part of it struck him. Winds, about 25 minutes after the accident, were recorded at an airport about 25 nautical miles to the northwest as being from 340 degrees magnetic, at 7 knots. At the same time, winds were recorded at another airport, about 35 nautical miles to the northeast, as being from 360 degrees magnetic, at 11 knots. Witnesses stated that the winds had been gusting during the time of the accident. Other airports in the region had recorded wind gusts up to 21 knots throughout the day. The pilot made an additional statement regarding the accident: "I believe this accident and many other gyro accidents were caused by 'dynamic rollover' - a rollover on the ground caused by severe rotor flapping caused by insufficient rotor rpm combined with excessive ground speed." He further stated: "This is a serious flaw in gyros which should no longer be covered up or pushed aside as unimportant." Further research on the subject failed to revealed any association between gyroplane operations and dynamic rollover. However, FAA Advisory Circular AC 90-87, Helicopter Dynamic Rollover, addressed how dynamic rollover could occur if a critical rollover angle was exceeded by a helicopter that pivoted about one skid or wheel, and which was still in contact with the ground. The private pilot had 87 hours of flight time in the accident gyroplane. He was rated in airplane category aircraft, but not in rotorcraft category aircraft. According to 49 CFR Part 61.31(k)(2)(i), the rotorcraft category rating was not required, even though a passenger was onboard, since the gyroplane was not type-certificated. In addition, the operating limitations for the gyroplane did not require the pilot to have an appropriate category or class rating.