On Sunday, November 14, 1993, about 1030 eastern standard time, N28215, a Gulfstream American Corp. AA-5B, owned and operated by James Connelly of Maynard, Massachusetts, collided with the ground and nosed over on landing following a power-off forced landing at Sterling Airport, Sterling, Massachusetts. Visual meteorological conditions prevailed and a flight plan was not filed. The certificated private pilot, and his three passengers received minor injuries. The airplane was substantially damaged. The personal flight originated in Fitchburg, Massachusetts, and was conducted under 14 CFR 91. According to the pilot, the airplane was at an altitude of 2000 feet MSL when he experienced a "severe vibration." He stated that the nearest airport was about 6 miles away, so he radioed the airport and reported that he was going to make a landing at that airport. He stated that he entered the traffic pattern on the base leg, and that the airplane was high on the approach. The pilot stated that during his training he was taught that "it is better to be high and fast than low and slow." The airplane touched down about half way down the 3100 foot long runway then exited into a six foot culvert and nosed over. The engine was removed to a hangar at Sterling Airport for further examination under the supervision of the FAA. The examination involved removing the lower spark plugs, and conducting a compression test. The examination revealed a leakage from both number one and two cylinders. The two cylinders were removed and sent to the NTSB Lab in Washington, DC for further examination. The examination involved the removal of the intake and exhaust valves from the number one cylinder assembly. The number two cylinder assembly and piston were submitted for comparison purposes. Examination of the number one exhaust valve revealed a fracture. Visual examination of the fracture with the aid of a bench binocular microscope revealed the presence of a crack that initiated in the radius between the stem and the head of the valve.