At 08:30 CDT, a Grumman American AA-5B lost its propeller assembly while in cruise flight near Claremore. The pilot was not injured in the subsequent forced landing. The pilot said he was in level cruise flight at 2,500 feet when he noticed a vibration in the aircraft. The vibration became more violent and the propeller flew off. The pilot elected to land at the Claremore Municipal Airport. The pilot said that the airplane started to porpoise during the approach, so he elected to touch down in the grass section between runway 34 and the taxiway to absorb some of the landing energy. The nose landing gear collapsed during the roll. The propeller assembly (propeller with approximately 5 inches of one blade tip missing, spacer, and forward bulkhead assembly) was located three miles west of the airport. The blade tip was found in the engine cowling. The propeller flange was found intact with the engine crankshaft.